The blast was over in a nanosecond, causing no more visible effects than the momentary frothing and churning of the turquoise waters around Mururoa atoll. But the political aftershocks from France's nuclear test in the South Pacific last week continued to reverberate around the world long after the waves had calmed.

In Berlin, 12,000 angry youths threw eggs and tomatoes at a French cultural center. In Chile, 10,000 protesters formed a human chain in a Santiago park. Thousands took to the streets in Sydney and Tokyo, while demonstrators in Manila burned a French flag. Japan's Finance Minister Masayoshi Takemura called the French action "crazy." Australian Prime Minister Paul Keating branded it "an act of stupidity." Chile and New Zealand recalled their ambassadors. The tiny Pacific island nations of Tuvalu, Nauru and Kiribati broke off relations with Paris.

But nowhere was the reaction more dramatic than in Papeete, Tahiti, the capital of French Polynesia, where several hundred rioters went on a rampage. In 36 hours of trashing and looting, they virtually destroyed Tahiti's international airport, smashed shop-front windows and torched several buildings before French Foreign Legionnaires and para military troops arrived. The upheaval, which injured 40 people and did millions of dol lars in damage, was attributed to a mixture of antinuclear and pro-independence sentiments.

The chain reaction of rage and indignation followed months of mounting protest. Ever since newly elected President Jacques Chirac announced on June 13 that his government would interrupt a three-year moratorium and carry out a "final" series of up to eight tests between September and May, France found itself the target of widespread international criticism, consumer boycotts and formal protests from more than 20 governments. Chirac's "irrevocable" decision has even been opposed by some 60% of the French public, and his standing in polls has slid to a low point of 36%.

In the South Pacific, the controversy took on the trappings of a naval battle as the militant environmental organization Greenpeace and a 25-boat "peace flotilla" approached the Mururoa test site. Four days before the blast, after Greenpeace penetrated a 12-mile security zone, black-suited French navy commandos boarded and commandeered the two lead vessels, signaling Paris' dogged determination to go ahead with the tests despite the inevitable global backlash.

Chirac justified his decision to resume testing entirely on scientific grounds. His predecessor Francois Mitterrand, he explained, had interrupted a critical series of tests "a little too early" by declaring a moratorium in April 1992. In order to ensure the reliability of its nuclear deterrent, said Chirac, France had no choice but to complete its "experimental program."

That analysis was based largely on the recommendations of French nuclear experts for whom Gaullist symbolism counts far less than the behavior of sub-atomic particles. For them, the challenge is to keep France's nuclear force credible beyond 2015 or so, when the present generation of warheads will have aged into obsolescence. Denying any intention of developing miniaturized or tactical weapons, French officials say the tests, costing $20 million apiece, have a threefold objective: verifying a new submarine-based warhead, the TN-75; checking the effects of aging on older warheads; and, most important, gathering the data necessary to perfect the simulation and computer modeling techniques that will permit France to forgo live tests in the future and sign the Comprehensive Test Ban Treaty.

Many analysts, however, took a more cynical view of Chirac's motivations. Recalling that it was Charles de Gaulle who first engendered France's "force de frappe" in the '60s, they accused Chirac of trying to prove his Gaullist credentials and burnish his presidential stature by reaffirming France's status as a nuclear power. "He thought he could prove to the French and the world that, because of his decision, France was back, and he was an authentic President," wrote Serge July, influential editor of the left-leaning daily Liberation.

Critics also challenged the French decision on technical grounds, questioning whether this series of tests would mark a fundamental advance in simulation technology. "A few more tests won't really make much difference in their program," says a U.S. State Department expert. "They can improve it, but they won't perfect it."

One of France's leading nuclear officials confirms this view. "The simulation process will not be operational before the year 2003 or 2005 in any case, and the time frame will not be affected by these tests," says Marc Launois, deputy director of military applications for France's Atomic Energy Commission. The reason for the delay, he says, is that it will take nearly a decade to complete the 1.8 megajoule laser near Bordeaux that will be the centerpiece of the so-called palen simulation system. Says Launois: "There is no connection between the tests and the installation of these big instruments." Conceding the feasibility of passing to the simulation phase without more live tests, Launois argues that "they are useful because they reduce the period during which our physicists will be working in a vacuum without live data."

France could shorten the path to full-scale simulation by acquiring the necessary technology from the U.S. Although the U.S. is willing to offer help, the French have declined. "This is a question of national independence," explains Launois. "We don't want to be dependent on the Americans and find that we can't go through with our plans if it doesn't please them."

But if their justifications for the tests are not entirely convincing, French scientists--and others--have largely refuted the notion that the underground experiments pose any immediate environmental threat. Since 1982, at least five expert studies--including one by anti-nuclear marine biologist Jacques Cousteau and one by the International Atomic Energy Agency--concluded that France's Pacific tests at Mururoa and nearby Fangataufa atoll, conducted from 1966 to 1992, caused no radioactive contamination and no significant ecological impact.

No one can be sure, of course, what will happen over the next century or so, when subterranean fractures in the basalt layer under the atolls could theoretically open up and release radioactive material into the sea.

Armed with reassuring studies, French officials insist that the tests pose no danger to the regional populations. They point out that the closest inhabited island is 120 km from Mururoa, and that there are only 2,500 inhabitants living within a 500-km radius--in contrast to the several million people living the same distance from the U.S. test site in Nevada. As for the New Zealanders and Australians who have taken the lead in protesting the tests, the French note that Auckland is 4,750 km away and Sydney 6,900 km. Finally, to those who say France should test on its own soil, the reply is that Mururoa is legally just as French as Paris or Lyon.

But such reasoned arguments are unconvincing to the Pacific nations. "I am prepared to accept that by some political concoction, the French control the area and therefore have a right to test there," says Sir Geoffrey Henry, Prime Minister of the Cook Islands, located 2,160 km from Mururoa. "But geographically it is not theirs. It is part of the Pacific. It is as if an invasion has taken place."

Rejecting French claims of the tests' ecological and political inoffensiveness, Australian Prime Minister Keating maintains that "every test poses its own degree of environmental risk; every test further undermines the credibility of the Nuclear Non-Proliferation Treaty." Not surprisingly, the most incendiary expressions of regional resentment have come from Tahiti, where independence leader Oscar Temaru told antinuclear protesters early last week, "Chirac is a criminal."

Paris seems to have been utterly unprepared to fight the public relations war that Chirac's decision unleashed. Traveling with Chirac to the G-7 summit in Halifax, Nova Scotia, shortly after the testing announcement last June, a senior French diplomat confidently told reporters that France "can live for six months without being liked by the Australians."

But it soon became clear that Paris had underestimated the magnitude of the protests--and consumer boycotts--that quickly spread from Australia, New Zealand and Japan to Germany, Austria, Britain and Scandinavia. Noting that China's underground blasts over the past 14 months had met with only pro forma criticism, French Defense Minister Charles Millon said that what really was at stake was an "economic war" and charged that "there are countries whose aim is to remove France from the Pacific more than to criticize nuclear tests."

In a particularly embarrassing communications snafu, no one had bothered to point out to the President that the 50th anniversary of the bombing of Hiroshima and Nagasaki would fall just weeks before the first test, stirring revulsion against nuclear war and inviting unflattering comparisons. "The timing was bad," sighs an Elysee official. "But even if we had decided to choose another moment, our hands were tied by the need to get the tests over before the Comprehensive Test Ban Treaty is concluded next year."

Paris is committed to the CTBT, and it played a key role in securing the indefinite extension of the Non-Proliferation Treaty earlier this year. Indeed, France has unilaterally downsized its nuclear arsenal since 1991 by 15%, to some 500 warheads (against about 10,000 each for the U.S. and Russia). Mitterrand mothballed France's arsenal of mobile Hades missiles, and Chirac has announced plans to close down the fixed missile silos on the Plateau d'Albion in southern France, leaving the country with only a submarine-based and airborne deterrent.

Last month the Chirac government announced its support of the "zero option" test-ban treaty, meaning that the document should bar even the low-yield tests that many military officials in France and the U.S. were hoping would still be permitted. Prodded by Chirac, whose decision he applauded, President Clinton overruled the Pentagon and followed suit on the zero option.

Thus it is ironic that Paris now finds itself accused of relaunching the arms race and encouraging nuclear proliferation. In the minds of many critics, in fact, the real danger of the French tests lies not in their threat to the environment but in the dangerous message they send to would-be proliferators. "Now go explain to countries like India that they shouldn't imitate us," says French astrophysicist Hubert Reeves. "These tests sabotage the fragile confidence among nations and threaten the success of the 1996 international [test ban] treaty. The military is one war behind the times. They haven't understood that the Berlin Wall has fallen!"

Even among French supporters of the force de frappe, some critics fear the tests may actually weaken the country's nuclear defense strategy rather than bolster it. "The political cost is bigger than the technical gain," says Pascal Boniface, director of the Institute for International and Strategic Relations. "The decision may wind up discrediting the very idea of deterrence." Says Dominique Moisi, deputy director of the French Institute for International Relations: "It opens dangerous doors that were closed before. There was a consensus on deterrence that no longer exists ."

The force de frappe has been the backbone of French defense ever since General de Gaulle shouted, "Hurrah for France!" on hearing of the success of the first nuclear test in the Sahara on Feb. 13, 1960. French nuclear doctrine is based on the threat of massive retaliation against any threat to the nation's "vital interests." Though never precisely defined, that was long taken to mean an invasion of French territory. Unlike the two superpowers, De Gaulle never designated a potential enemy. Though French missiles were supposedly aimed tous azimuts--in all directions--they were in fact targeted exclusively on the Soviet Union. Today there is no longer such fixed targeting, but trajectories can be set on short notice in the event of a threat.

But in the post-1989 world, the potential source of such threats is far from clear. "Who and what are their enemies?" demands Stephanie Mills, Greenpeace International's nuclear-testing campaign coordinator. "They are talking cold war rhetoric that no longer has any political relevance." French officials retort that the world remains a dangerous place."No new world order has yet replaced that of the cold war," wrote Prime Minister Alain Juppe in Le Figaro last month. "New powers are appearing on the scene, and they are not always well disposed toward us. We have the duty to tell our fellow Europeans that new threats will replace, or have already replaced, old ones."

Juppe's appeal to "fellow Europeans" signaled a major shift in French nuclear doctrine. In recent weeks, Paris officials made increasingly explicit the idea of extending France's nuclear umbrella to cover its European partners-something that would have been anathema under the old Gaullist strategy based on national independence. As Juppe put it, "the future European defense will not be built without the French deterrent--and the British-playing some kind of role." He said that France wanted to "open this debate" once the tests were over.

The offer of French nuclear protection was met with quiet skepticism by most European partners, who questioned the sincerity of the timing. "I don't see the possible use of it now that the Soviet Union has collapsed," Conservative Brit ish M.P. Sir Teddy Taylor told the weekly L'Express. "It was clearly aimed at Germany and at public opinion there, considering the strong reaction of the Greens," says a European Union diplomat in Brussels, referring to polls showing 95% of Germans opposed to the tests. Indeed, it was only from Germany that there were any discreet expressions of interest. "In our view," said Bonn Foreign Ministry spokesman Martin Erdmann, "we would be pleased if the vital interests of France were not restricted to threats to the territorial integrity of France." But even in Germany, skeptics abounded. Harald Muller, director of the Hesse Foundation for Peace and Conflict Research, called the French offer a "touching attempt at blackmail."

Even as it made overtures to the Europeans, Paris launched a p.r. counteroffensive under the banner of "transparency." In an almost unprecedented move, French officials organized several press junkets to Mururoa, where reporters armed with Geiger counters splashed in the pristine surf and marveled at the near-zero radiation readings-prompting one Quai d'Orsay official to quip that the complex should be turned into a Club Mediterranee village once testing ended.

In addition, the government provided a considerable amount of technical information about the testing methods and objectives. For the first time, Paris published a complete list of the 45 atmospheric and 134 underground tests it has conducted since 1960. The champion button pusher, it turns out, was Mitterrand, who ordered 86 tests before announcing the moratorium three years ago.

"The military opposed Mitterrand's decision," says his former top aide Jacques Attali. "But the President asked them if the nuclear deterrent would cease to be credible if they stopped testing. They said no, it would be good for another 20 to 30 years. So he stopped the tests." At a May 1994 press conference, Mitterrand confidently predicted that his successors would "not be able" to end the moratorium. He now concedes privately that the announcement was an error because it prodded Chirac to prove him wrong.

Chirac addressed the issue last Tuesday in his first TV interview as President. "France does not want to improve its deterrent force, which is already sufficient," he told France 2 reporter Patrick Chene. He said he had "decided to resume [testing] because the security and reliability of our deterrent depends on it." Though there was no question of reversing that decision, Chirac held out the possibility of reducing the number of tests to six or fewer if "we have all the information we need." In any event, Chirac promised the experiments would end "well before" the original cutoff date of May 31, 1996.

Within hours of that interview, at precisely 10:30 a.m. local time, technicians at Mururoa set off an underground explosion somewhat smaller than the bomb that destroyed Hiroshima. "Operation Thetis" took place inside a metal canister 20 m long and 1.5 m wide. The canister, containing the nuclear warhead, monitoring devices and optical-fiber cables, was inserted into a well drilled 800 m into the atoll's basalt foundation. Once the canister was in place and the cables connected to a remote command system, the shaft was filled with layers of cement, sand and rubble from the drilling.

Triggered by a remote-control system, the blast generated temperatures of several hundred million degrees and pressures of several million atmospheres. The recording instruments transmitted their data for only a nanosecond (one billionth of a second) before being destroyed and encased in molten rock, along with the radioactive debris. Within minutes, seismographs around the world were picking up the shock waves, which measured about 5.0 on the Richter scale. At 11:45 p.m. Paris time, the French Defense Ministry issued this terse declaration: "France has proceeded with the underground nuclear test at Mururoa atoll, whose equivalent level was less than 20 kilotons."

Though everyone knew it was coming, the news sparked expressions of shock and indignation--especially from the Pacific nations. "Once again the stomach of our foster mother has been raped," declared a statement from the Evangelical Church headquarters in Papeete. New Zealand Prime Minister Jim Bolger said the decision "defies explanation" and vowed that his government would continue to appeal to the International Court of Justice for an injunction against the tests. Australia's Keating accused France of showing "contempt for the countries and people of the region and for all those who hope and work for a nuclear-free world." At a sit-in by 40 A-bomb survivors in Nagasaki's Peace Park, Hiroshima mayor Takashi Hiraoka called the test an "unforgivably reckless action."

Seemingly unshaken by the wave of outrage, Chirac called the protests "hysterical" and insisted that "France will be absolutely firm" in completing its test program. "There are times," said Prime Minister Juppe, "when the grandeur of a statesman is to confront a passing unpopularity in order to preserve, in the medium and long term, the essential interests of the country." Far from retreating, the President appeared ready to fight back at his critics, canceling a planned state visit to Japan and disinviting Swedish Prime Minister Ingvar Carlsson to Paris after the Japanese Finance Minister and Swedish Culture Minister joined an anti-French protest march in Tahiti.

Such feistiness is fully in character for the man whom former President Georges Pompidou once dubbed le bulldozer. For whatever reasons, Jacques Chirac has made an "irrevocable" decision, and nothing will make him back down now. He may reduce the number of tests, or get them over as soon as possible. He will talk of national independence and try to appear resolute. And in the end he will probably weather the storm. But France's international image will have a paid a heavy price. And those who dreamed, 50 years after Hiroshima, of a world without nukes may have a little longer to wait.

--With reporting by Al Prince/Papeete, Simon Robinson/ Auckland, Bruce van Voorst/Bonn and Douglas Waller/Washington