Next week Washington is planning to put on a monstrous birthday party. Seventeen-hundred diplomats and their hangers-on will celebrate the 50th anniversary of NATO. There will be endless dinners, speeches, receptions, galas. But one piece of revelry is likely to be dropped: the planned flyby of NATO aircraft.

At a time when their counterparts are dropping bombs on bridges and buildings in Serbia, this is considered poor taste. Nothing like a war to remind one that these shiny toys are not entirely ceremonial. They are intended to kill.

In fact, there's nothing like a war -- NATO's first, and a losing one at that -- to put a crimp in a birthday party. Especially one that the Clinton administration had planned as the occasion for a display of its intellectual firepower: unveiling a shiny new "Strategic Concept" for NATO. In the words of the deputy secretary of state, "a new NATO for a new era."

What was wrong with the old NATO? NATO was born as a defensive alliance to protect Western Europe from Soviet invasion. Having decided that NATO is now obsolete, the administration would create a new NATO -- active, aggressive, ready to fight beyond its home territory against such various threats as "ethnic strife and regional conflict." As in, say, Kosovo.

Is NATO really obsolete? Its original role was famously defined by its first secretary-general, Lord Ismay: "To keep the Russians out, the Americans in and the Germans down." All three purposes survive.

The Soviet Union is dead, of course. But Russia's destiny is still unsettled. Western Europe requires NATO as a defensive alliance if Russia goes bad. On the other hand, if Russia turns out well, NATO is the best means for gradually integrating a friendly Russia into the Western security system.

NATO's continuing purpose is to keep America trans-Atlantically committed: as guarantor of Europe's defense and as provider of the security umbrella under which the European powers pool their military resources rather than, as of old, pitting them against each other.

NATO's final -- intra-European -- role endures as well. In the early postwar years, that meant reintegrating a subdued Germany. That role is larger now. It means averting the military rivalries, arms races and geopolitical competition that had existed between the great European powers (most notably Britain, France and Germany/Prussia) for more than 300 years.

For the clever young thinkers of the Clinton administration, however, this is all too boring. Suffering Acheson envy, they insist on recreating the Western security structure that Acheson and company so brilliantly conjured up 50 years ago.

Albright and company have declared NATO's old mission over. The new one is not defense but world order: NATO as a robust, restless alliance ready to throw its weight around outside its borders to impose order and goodness, or as Albright put it, "democracy, stability and basic human decency."

A lovely, heartwarming theory -- so unfortunately exploded in its first reality test, Kosovo.

Kosovo stakes NATO credibility -- and thus its life -- on a mission far more elusive, far more risky and far less central than anything it had attempted in its 50-year history. It won its 50-year defensive war against the Soviet Union without firing a shot. It may lose the Kosovo war in a month against the ruin of a rump state with a GNP one-third the size of Cameroon's.

Kosovo reveals how deeply unsuited a lumbering and clumsy NATO is to its new extraterritorial task. The idea of this bureaucratic behemoth -- a 19-member alliance that operates exclusively by consensus, which means that all 19 have to sign off on everything -- trying to be nimble and flexible in managing such brush fires as Kosovo is simply crazy. The result is the Kosovo campaign, already famous for its ineptness: its absurd recapitulation of Vietnam escalation strategy, its confusion of aims, its timidity of means, its slowness to respond to unexpected contingencies.

NATO is well suited to the purpose of resisting a life-or-death invasion of its territory, something that requires fixed and long-term planning, strategy and preparation. But Kosovo? NATO is not the French Foreign Legion. Indeed, the French Foreign Legion might have done better protecting Kosovars than the lumbering giant now blowing up empty buildings and the occasional train hundreds of miles from the scene of the Kosovo crime.

NATO doesn't need a new strategic concept. It needs leadership that is confident enough in the old strategic concept -- vigilance against possible threats from the east -- to articulate it. And leadership that is not inclined to stake the survival of the most successful alliance in history on bright new academic ideas cooked up far from the battlefields on which they now flounder.