WASHINGTON — NATO appears to be gaining a new lease on life as the United States reasserts its leadership and sets the Atlantic alliance on a new post-cold-war course.
After months of waffling, the alliance is suddenly making tough decisions, just like the old days.
If Clinton officials are correct, Sept. 20 is the day that best symbolizes NATO's newfound purpose.
To many Western officials and analysts, that day proved that NATO had put behind it months of internal disputes over dealing with Europe's worst crisis since World War II: the war in Bosnia-Herzegovina. But on a broader level, they say, it showed that the defense pact founded to contain Soviet aggression is beginning to adapt to new, post-cold-war challenges.
In 24 hours, the pact's 16 members achieved much: They approved guidelines for admitting former Communist bloc states; began planning an unprecedented peacekeeping operation in Bosnia; and agreed to accommodate a Russian demand for adjustments to the Conventional Forces in Europe Treaty.
The unusual cooperation was crowned at 10 p.m. by a final satisfaction: confirmation that the Bosnian Serbs had capitulated to NATO air attacks by completing a withdrawal of heavy artillery from around the Bosnian capital of Sarajevo.
''Sept. 20 might have been the most remarkable day in NATO's history,'' says a senior US official. It underscored that ''we have a grip on security conflicts in the future.''
Agrees Ed Kolodziej, a European security expert at the University of Illinois in Evanston: ''NATO is going to be the organization of preference for security in Europe.''
Experts attribute the ''revitalizing'' of NATO to the US decision to take control of Balkan peacemaking efforts. The previous US policy of watching UN and European Community failures not only brought humiliation to the Clinton administration, but fueled deep doubts about US leadership of NATO and its commitment to European security.
That NATO's new cohesion depends on US leadership constitutes the underpinning of President Clinton's insistence on US participation in a Bosnian peacekeeping force.
''[As] NATO's leader, the United States must do its part and send in troops to join those of our allies under NATO command with clear rules of engagement,'' Mr. Clinton said last week. ''If we fail, the consequences for Bosnia and for the future of NATO will be severe.'' (See related story, Page 5.)
Success in Bosnia may well be the next test of NATO's post-cold-war transformation, but it must still overcome its own institutional inertia and implement internal reforms, experts say. And such restructuring is just one element of a greater challenge: the US-inspired plan to expand the alliance eastward.
The proposal faces several hurdles. Chief among them is vehement Russian opposition. Moscow sees the extension of NATO membership to former satellites that sit along its borders as a threat.
NATO officially denies that its expansion is aimed at Russia, but US officials privately concede that a larger NATO could be a hedge against a return by Russia to its historic expansionist tendencies.
To assuage Russian concerns, US officials are negotiating with Moscow a special relationship with NATO that stresses increased cooperation and consultation. In addition, a NATO study approved last month on the ''how and why'' of expansion says the alliance has no plans at this time to station nuclear weapons on the territories of new members.
But the Russian government and its political opponents remain dissatisfied, and their misgivings have has been exacerbated by NATO's intervention in Bosnia. Defense Secretary William Perry and his Russian counterpart, Pavel Grachev, reported making slow headway in talks Sunday in Geneva on a Russian role in the proposed Bosnia operation.
NATO enlargement faces other hurdles. Reforms in many Communist states are proceeding slowly. The senior US official warns that European security also hinges greatly on EU efforts to extend trade and economic aid to Eastern European states. Says he: ''If the European Union does not do its job, it doesn't matter if we [NATO] do ours.''