CHALLENGE ANY historian to name an alliance more successful than NATO.
There is none.
Yet in every decade since the 1950s, throngs of foreign-policy experts have asserted that NATO faced some new crisis.
Now comes the crisis of the '90s -- the fragility of democracy in Eastern Europe and Russia, and the loss of a common enemy -- and therefore, it is said, NATO must admit Poland, the Czech Republic, Hungary and other nations of the former Warsaw Pact.
This remedy may seem all the more urgent as Russian forces keep inflicting wanton destruction on Chechnya.
Americans who question the wisdom of this eastward expansion fear that it might cause Russia to refurbish its military and expand westward. But this is only half the problem.
Far from solving an alleged crisis, expanding NATO now would fatally weaken it. The Atlantic alliance must not become a chain letter -- some Ponzi scheme that escapes bankruptcy only by signing up new members.
And NATO should not troll behind the European Union trying to hook the same fish. The bureaucrats of the European Union plan to catch Malta, Cyprus and Slovenia, as well as bigger fish in Eastern Europe.
Not to be outdone, the Clinton administration promoted the Partnership for Peace, an ill-defined assembly that includes just about every non-Asian country in the Northern Hemisphere.
So does the Organization for Security and Cooperation in Europe, which is . . . Now, who remembers what that organization is all about?
But people do remember what NATO is about. On both sides of the Atlantic, people know that NATO is about peace with freedom, victory over communism, borders defended without fighting a single battle.
Should the Atlantic alliance someday again face the threat of external aggression, this achievement would give fortitude and cohesion to all the member nations as they gather their military strength.
If the United States now pressured its reluctant European allies to consent to some scheme of eastward expansion, it would jeopardize the bonds that link America to Europe.
Inviting new members into a consensus-based alliance is always risky. It is foolhardy if the new members have not worked together in a collective endeavor to overcome a common danger.
Of NATO's 16 members, most were allied or closely associated in World War II. The Axis powers Germany and Italy were welded into the Atlantic community through the Allied occupation and the Marshall Plan, and Spain agreed to close military cooperation with the United States three decades before being admitted to NATO.
Greece and Turkey received an enormous amount of U.S. aid for five years before joining NATO. For the East European nations today, such an infusion of money is out of the question.
Admitting former Warsaw Pact countries would weaken NATO in other ways. It might let in a Trojan horse. If one fears an emerging military threat from Russia -- as many who favor NATO's expansion do -- one must also expect that a revived KGB would find collaborators among its former colleagues in Eastern Europe.
Far-fetched? Last year Marian Zacharski -- who had been imprisoned in the United States as a Warsaw Pact spy in the 1980s -- was named head of the Polish intelligence service. He was later removed because of criticism at home and abroad.
And just two weeks ago, Poland's prime minister nominated Longin Pastusiak, formerly a Communist ideologue and foe of NATO, as the next defense minister.
Advocates invariably assert that an expanded NATO would fill a vacuum in Eastern Europe. But if, say, Slovakia is a vacuum, why not Slovenia? If Slovenia, why not Macedonia, Moldova or Belarus?
By expanding eastward, NATO would merely shove the vacuum ahead of itself.
Another rationale is that democracy in former Warsaw Pact nations must be nourished and consolidated by NATO's embrace. In fact, NATO membership neither guarantees nor requires democracy.
Greece had been a member of the alliance for 15 years when a 1967 coup led to seven years of military rule. Yet it remained a member the entire time the colonels were in power.
The advocates of expansion want Western Europe to support it as a moderate step, and Russians not to fight it as a hostile plan. To this end, the advocates are willing to strip NATO of its military essence by ruling out deployment of allied forces on the territory of the new member states.
The alleged political vacuum between Germany's eastern border and Russia's western border would thus be filled by a real military vacuum.
The alliance would split into two parts. The western realm would retain -- initially, at least -- a common defense anchored in the deployment of U.S. forces integrated with European forces.
The new eastern realm, by contrast, would be forced to forgo this bedrock of Atlantic security.
Although Congress has so far supported the continued stationing of U.S. forces in Germany, it would not take long for most Americans to conclude that what is good enough for the impoverished and exposed new eastern wing of NATO is good enough for rich Western Europe.
The American troops would come home.
This would be welcomed by those who want the North Atlantic Treaty to be no more of a deterrent to aggression than the U.N. Charter.
Fred C. Ikle, a scholar at the Center for Strategic and International Studies, was undersecretary of defense in the Reagan administration. He wrote this for the New York Times.