The Western alliance marks its 35th anniversary this week amid considerable introspection and foreboding about the status of the more than 300,000 American troops in Europe and basic allied policies.
Created on April 4, 1949, during a period of major East-West hostility, the NATO alliance has survived several other phases of internal and external tension , as well as equally troubling periods of complacency.
If its current leaders are indulging in a bit of self-congratulation at having kept this sometime squabbling coalition together and managed to escape an East-West military conflict, they are also conscious that solutions may at last have to be found to some nagging problems.
Both in NATO headquarters here and in 16 member countries, strategists are in the midst of a fundamental reexamination of NATO doctrine and machinery.
The current phase is perhaps not so dramatic as the ''agonizing reappraisal'' demanded by US Secretary of State John Foster Dulles in 1954, President de Gaulle's split with the alliance in 1966, or Henry Kissinger's ''Year of Europe'' outburst 10 years ago. But many regard it as a historic passage following the difficult deployment of a new generation of US nuclear missiles on European soil and the interruption of many East-West negotiations in the wake of leadership transitions in both the United States and the Soviet Union.
This sometimes caustic debate surrounds both military and political attitudes. As in some past episodes, it involves the burdens carried by the United States and Europe toward defense against the Warsaw Pact.
Not since the proposals of the late 1960s - when Senate majority leader Mike Mansfield sought to reduce Europe-based US forces unless other Western governments helped shoulder more of the responsibility - has so much attention been cast in this direction.
The issue reached a peak in recent suggestions by former Secretary of State Henry Kissinger that these US forces might be reduced by half.
''If nuclear weapons remain the ultimate deterrent to even conventional attack,'' he said, ''a gradual withdrawal of a substantial proportion, perhaps up to half, of our present ground forces would be the logical result.''
Although some elements of the Kissinger suggestions about the so-called ''Europeanization'' of Western defense have been supported by Europeans, including former West German Chancellor Helmut Schmidt, his comments have also aggravated European sensitivity.
Dismayed West German officials have shown skepticism about the wisdom of improving conventional NATO capability to match the existing Warsaw Pact superiority on the grounds that such improvements would reduce the credibility of the American nuclear deterrent. Quite clearly, they and other Europeans are also not optimistic about their governments' ability to raise defense spending in a period of economic austerity.
But the discussions about a possible cutback in the US military presence for once may have surfaced at a more propitious time than in the past. They coincide with renewed interest, stimulated by French President Francois Mitterrand, in greater European defense cooperation.
This drive for greater European cooperation is meant to convince Americans that their allies are enlarging their efforts to prevent the threatened US reduction and also as a precaution in case US forces were cut anyway from Europe.
It also seeks to reduce the traditional European arms dilemma of either depending on American equipment or engaging in wasteful national production.
Another French goal is to solidify West Germany's participation in the Western camp and halt what it fears is a drift toward neutrality in Bonn's quest for reunification with communist East Germany.
In recent months France and other neighbors have moved beyond the discussion stage to revive two moribund institutions, the Western European Union and the Independent European Program Group, in which the United States does not participate. A ministerial meeting is in the works for the former, and the latter recently prepared a still-confidential report on European armaments cooperation.
What Europeans have always sought is improved unity in defense spending and production in order to deal as a solid front with Americans on such economically important issues. In the past, such initiatives have run up against national industrial self-interest in both Europe and the United States.
This time, however, budgetary pressure on both sides of the Atlantic has made the possibility of European and transatlantic cooperation on arms production more compelling.
In the past year US Ambassador to NATO David Abshire has made the issue of ''resource management'' among the allies the hallmark of his tenure. He has also recognized that ''Europe must get its house in order'' to work on an equal footing with the United States in this area to eliminate costly duplication and ensure the credibility of NATO conventional deterrent strategy. In recent years this has focused more and more on the introduction of costly so-called ''new technologies'' into the NATO arsenal.
The push for closer European defense coordination has met with some reservation, however, from West Germany and Britain.
Germany, although interested in greater European arms cooperation and efficiency, is reluctant to give up any competitive edge it may have over its neighbors in a pooling effort. And it is equally reluctant to offer any pretext for weakening traditional US involvement in Europe or NATO doctrine in return for some nebulous goal of European unity. Germans have generally approved of France's newfound interest in Western defense after years of Gaullian aloofness, but they fear closer German involvement in future French or European nuclear strategy.
Similar skepticism characterizes British thinking. It is still unclear whether British Defense Minister Michael Heseltine will attend the scheduled Western European Union ministerial session devoted to these issues in June. In London there has always been hesitation to jeopardize ''the special relationship'' deemed to exist with the United States or to encourage any semblance of a closer Franco-German axis.
Many of these issues are expected to be scrutinized in NATO itself in the coming months with the advent of the former British foreign secretary, Lord Carrington, as NATO's new secretary-general and a special study of alliance strategy for the 1990s assigned to Belgian Foreign Minister Leo Tindemans.