Nearing 1 a.m., Sunday, Sept. 3. Just beyond the French navy's 12-mile exclusion zone at Mururoa, the South Pacific atoll where France plans to test nuclear bombs. Light wind. Half-moon. Waves from a far-off storm swell under La Rebaude, a broken-engined, radio-dead ketch owned by Greenpeace. The crew hands two black-painted sea kayaks over the rail. They are then tethered to a Zodiac inflatable boat already pitching in the water.

Al Baker, 31, a veteran Greenpeace activist, starts the Zodiac's 15-h.p. motor, and Matthew Whiting climbs aboard from the ketch. Whiting, 36, is lately of the French Foreign Legion; for that matter, he is lately also of the British Army, the Spanish Foreign Legion, and the University of Hertfordshire, where he studies literature. The two men, both British, carry green fatigues in waterproof bags. They have short haircuts. Whiting, burly and broken-nosed, speaks fluent rough-and-tumble French that he learned in the Legion while serving on Mururoa. Baker, a lean, hard mountain climber with a seen-better, seen-worse expression, speaks nothing but rich, working-class Sussex.

Someone says, "Cheers," Baker revs the outboard, and the little inflatable, low in the water, rocks away on the swell, towing the kayaks toward Mururoa. The air is still, and for 10 minutes more the whine of the Zodiac's engine can be heard on La Rebaude. Then, nothing.

Beyond Mururoa's reef, a high seawall protects the atoll from natural storms and from tidal waves occasionally heaved up by the underground nuclear explosions. A second, lower seawall also surrounds the atoll. The single entrance to the lagoon within is only a few meters wider than the beam of a medium-size oceangoing ship. Protest vessels have been aiming at this breach since 1972, and last month Greenpeace flagship Rainbow Warrior II, a successor to the Rainbow Warrior blown up by the French at Auckland, New Zealand, in 1985, was rammed by a French warship as it tried to enter the lagoon.

But Baker and Whiting are not headed for the entrance. They will abandon their Zodiac 6 or 8 km at sea and negotiate the reef with the kayaks. Reaching land, they will hide the kayaks and climb both seawalls with grappling hooks. With luck, they will have a day or so for mischief before they are caught. The men plan to tag Mururoa's buildings with Greenpeace stickers and graffiti, slip notes to some of the press people invited by the French to witness the explosions, write a few postcards of Mururoa and drop them into the PX mail slot, get the French to search for them, and perhaps stall the first test. The stunt is planned as a classic Greenpeace "action," a dead-serious, nonviolent prank executed at considerable peril.

The plan is, if the two infiltrators are about to be captured at sea or on the beach, they will fire a parachute flare to signal their comrades on La Rebaude. There is no flare. The lights of a French patrol boat appear to the north, at the 12-mile limit. It motors to within 275 m of La Rebaude, showing its presence. Then it falls away.

A 13-m ketch, La Rebaude had sailed from Papeete, the capital of Tahiti, at midnight 11 days before, without clearance from the French, and rendezvoused with the two kayakers at sea a few miles down the island's coast. Greenpeace bought the boat somewhat casually at dockside in Papeete and equipped it in four days, without sea testing and without including a long-range radio transmitter or receiver. (The diesel engine died four hours into the voyage, so the vessel also lacked electric power except a little generated by solar panels, and thus had no functioning refrigerator or electric bilge pump). A tiny shortwave radio occasionally brought in a scrap of intelligence. Somebody had reached the quarter-finals at the U.S. Open. An Australian rules football team had lost.

News came in half-intelligible fragments: the Rainbow Warrior had been seized and impounded and was being towed to Hao, a French prison base 563 km north of Mururoa. Greenpeace had planned to sacrifice the Warrior, a converted North Sea trawler rebuilt with three masts, electronically controlled sails and huge banks of communications gear. This was calculated legend weaving. If the French wrecked or sank a second Rainbow Warrior, the inevitable third one would have supernatural public-relations power. But a second bulletin came through the static: the MV Greenpeace had been boarded and seized.

This was not the plan. The Greenpeace, a rebuilt ice-class tug given to the organization by the Chesapeake Bay Pilots' Association, was a floating base for other Greenpeace ships, and for the two dozen private boats expected to join the protest flotilla. These small boats, like La Rebaude, would arrive low on fuel and stores, needing communications, repairs and a curative cold 12-pack. Now the fleet had no floating base. Something had gone badly wrong.

Isolated and ill informed as they sailed to Mururoa, La Rebaude's hands spent the long night watches telling Greenpeace stories, many of which shared the same moral: "The military lies. Corporations lie. We don't lie." Twilly Cannon, from Missoula, Montana, the boat's captain, had spent months in 1990 stalking the Soviet navy as it prepared to ditch another spent nuclear reactor in the Kara Sea northeast of Murmansk . Michelle Sheather, an Australian, was a crew member on the Rainbow Warrior when the French blew it up, and had left the ship 15 minutes before the limpet mines went off.

And Whiting told why he was bitter enough to risk his neck. He is convinced--without any real evidence--that the French used the Foreign Legion troops on Mururoa as nuclear guinea pigs. They were a labor force, reinforcing the island's coral with concrete and rebuilding roads that buckled after bomb tests. But the legionnaires worked in areas contaminated by radiation, Whiting insisted. Someone not French had to clean up debris after explosions. Blood and urine samples were taken weekly, but no results were revealed. He was beaten up, he said, for asking a single question about the effectiveness of Geiger counters.

A few hours after dropping off Whiting and Baker, La Rebaude reaches a flotilla of protest boats at a spot in the open blue ocean--139.05 degrees W, 22.30degrees S--about 24 km off Mururoa. One--masters and two-masters crowd the site. French picket boats motor slowly at the line of the exclusion zone. A French jet labeled marine mock-strafes the boats one by one, diving from about 305 m to not more than 46 m, then rising and diving again. Military helicopters buzz about, low enough for the mustaches of the harnessed, helmeted commandos to be visible through the open cargo doors.

With both the Rainbow Warrior II and the Greenpeace in the possession of the French, the new hubs for the fleet proved to be the Manutea, a boat for journalists, and the Vega, skippered by Dave McTaggart, a former Greenpeace chairman who had sailed the Vega into Mururoa's exclusion zone in 1972 and '73. He was rammed the first year and beaten nearly to death by the French a year later. "They hate my boat," he says with a grin. "And I have some symbolic value."

Early on Monday, McTaggart organizes an action that sends four fast Zodes, as Zodiacs are called, piloted by veteran Greenpeace drivers, two women and two men, into the lagoon . A test appears to have been scheduled for later that morning. If so, it is postponed. Then the fleet, egged on by McTaggart, makes late-evening feints, en masse, at the exclusion zone, turning away at the last minute. "Getting the French out of bed," he calls this taunting.

Tuesday morning brings two developments. One is that Whiting and Baker have been caught. They evaded the French for two days. That is a victory. A bit later the news comes that the French have exploded their first bomb, a small one about the size of the one dropped on Hiroshima.

Yes, McTaggart says, Greenpeace will stay on Mururoa. Yes, they will make another run at the exclusion zone, with three boats, maybe four, including the black-hulled La Rebaude. He answers the radiophone. "Look," he says to someone in Papeete, "I need to know exactly which of those parliamentarians is prepared to violate the zone. Yeah, yeah, call me tomorrow."