In their calmer moments, Russian officials are merely gloomy about the prospect that NATO, the Western military alliance that stared down Moscow for 40 years, will expand eastward to take in many of the old Soviet Union's former Warsaw Pact allies. But in their more emotional outbursts, they are becoming positively dyspeptic on the topic. Boris Yeltsin has warned that expansion could light "the flame of war." Alexander Lebed, the popular general turned politician who in Russia's skewed spectrum is considered a "moderate" alternative to ultranationalist Vladimir Zhirinovsky, has said that if NATO moves east, "World War III would begin."

NATO last week ensured that the Russian sabers will keep rattling. The 16-member alliance took an important step toward admitting new members with the publication of a 30-page study on the "how" and "why" of expansion, outlining the criteria for applicants. "It is the strongest signal so far that NATO is damned serious about expansion," says Andras Simonyi, Hungary's ambassador to the alliance. Though the study purposely sidesteps the key questions of who will get in and when, it adds momentum to a historic shift in Western security that so far has received little public debate in Western capitals, least of all Washington. Expansion of NATO would extend America's nuclear umbrella far into Central Europe and might commit allied soldiers to fighting ever more distant battles. In the experts' shorthand, London and Paris would be joined in importance, security-wise, by Bratislava, a city few American voters, or Congressmen, could locate on a map.

Still, the immediate problem is relations with Russia, where the West is already concerned with other contentious issues, including leakage from Russia's huge nuclear-weapons stockpile, conflicting policies in Bosnia, compliance with an earlier conventional-arms pact and ratification of the vital START II long-range nuclear-missile treaty, to name but a few. Yet atop that list, "the problem of NATO enlargement is becoming the key issue in relationships between Russia and the West," warns Alexander Konovalov, the military-policy director at Moscow's Institute for the U.S. and Canada.

While Russia's rabid nationalists have been most vociferous against NATO's proposals, the opposition stretches from the military to moderates to reform-minded democrats. "For the first time in years we have a consensus in the country," marvels Sergei Rogov, director of the U.S.A. Institute. "None of the major forces in Russia supports NATO's enlargement without Russia's participation." Last week Russian ambassador Vitaly Churkin sat stone-faced through a briefing on the expansion study at NATO's Brussels headquarters and afterward snapped, "We're still against it."

To be sure, NATO's expansion blueprint contains soothing language designed to alleviate Russian anxieties. It promises, for example, close cooperation with Moscow and states that "for the foreseeable future" there is no need to move nuclear weapons into new areas. NATO Secretary-General Willy Claes last week repeated assurances that "NATO will remain a purely defensive alliance. A larger NATO will threaten no one." But the bottom line of the NATO document is uncompromising. New members will be coequal with current ones in all respects. NATO troops may be stationed in their territory if the alliance chooses--and so may nuclear weapons.

NATO says its main reasons for expanding are to foster stability among the fledgling democracies of Central and Eastern Europe, both by encouraging the transition from communism to civilian-controlled armies with free economies and by helping them solve ethnic and regional disputes peacefully. Additionally, of course, NATO membership would provide vital insurance if Russia, militarily impotent today, later turns belligerent.

To a Russia reeling from a collapsed economy, social chaos and the humiliating loss of superpower status, NATO's claims of benign intent sound like so much "Western blather," says Rogov. Stung particularly by playing a poor second fiddle in Bosnia, Moscow sees a new doctrine of containment and confrontation quite different from the once touted inclusive-security system that would stretch from Vancouver to Vladivostok. It has not been admitted to any important Western institutions, like the G-7, and it feels its every action invites a barrage of criticism from the West, especially the U.S. A typical grievance: Washington opposed a Russian nuclear sale to Iran that had been blessed by the International Atomic Energy Agency, even as America was giving similar reactors to North Korea.

Yeltsin foreign-policy adviser Sergei Karaganov argues that NATO expansion will, in a stroke, "create a new subsystem for European security" that will exclude Russia, erode its trust in the West and further isolate it, causing Russia "to lose its major benefit from the end of the cold war--its de facto neutral buffer zone--and lead it to develop its own alternative security system." Moreover, the country's reformers feel let down by the West and fear expansion will hurt Russia's fragile democracy by strengthening the nationalists and the communists.

Although the West insists, as German Defense Minister Volker Ruhe emphasized last week, that "Moscow get no veto right or joint-decision power over NATO's plans," concern over Russian reaction looms large in the decision to expand. Influential doubters remain: U.S. SeNATOr Sam Nunn, a respected defense expert and a member of President Clinton's own Democratic Party, warned this summer that by provoking Russia, NATO could be "helping to create the very threat we are trying to guard against," while German opposition parliamentarian Peter Glotz calls expansion "an incredibly stupid idea." The difficulty, in the view of many, is that NATO is at risk whether it moves on or languishes. A major force behind expansion is the need to give NATO a reason to exist in the post-cold war era and thus keep the U.S. engaged in Europe, a top priority in both Eastern and Western Europe. "NATO without expansion is nothing," says Paul Cornish, of the Royal Institute for International Affairs in London. But, he adds, "expansion without some kind of Russian consent is dangerous."

NATO's response to this dilemma is twofold. On the one hand, it is pushing hard to build a "parallel" relationship with Moscow beyond Russia's current role in the Partnership for Peace program, a kind of NATO auxiliary club. The day before it released the enlargement study last week, the alliance conspicuously offered a draft proposal for a "political framework" with Russia that could eventually lead to something like a standing consultative committee or a nonaggression pact. Though the aim is to give Moscow the elevated status it craves, Konovalov warns, "The West can either have partnership with Russia or NATO expansion. It can't have both."

The other response is a time-honored one: delay. Resolute in their promise of expansion, the allies have been vague on the timetable and who will get to join, although Poland, Hungary, the Czech Republic and Slovakia surely top the list. U.S. Republicans and many of the applicant countries want speedy admission, but NATO says expansion will be "deliberate," i.e., slow. Last week's study will lead to another study. Realistically, the first aspirants may get a decision by 1997, but the needed ratification by 16 NATO parliaments may put off actual admission until 1999. In a world where the political and security picture is in constant flux, Cornish observes, such "muddling and fudging and keeping your options open" may be the best policy of all.

--With reporting by Sally B. Donnelly/Moscow, Dean Fischer/ Washington and Bruce van Voorst/Bonn