After four years of trepidation, NATO is going ahead with the deployment of modern cruise and Pershing II nuclear missiles in Western Europe. The Reagan administration wants to consider the deployment a major victory for the Atlantic alliance -- a sign that NATO can still unify against a Soviet threat. But there are apprehensions in West European countries that missile deployment may turn out to be a costly Pyrrhic victory.

As the U.S. government rejoices in seeing its perseverance vindicated, the European allies sense their troubles are just beginning. The prevailing mood, in all but the most optimistic circles, is that the new missiles will not resolve security concerns but rather will exacerbate tensions in a way that could ultimately encourage political estrangement between the United States and Europe.

The Europeans are looking beyond the next few weeks to a five-year period of political turmoil. Deployment is scheduled to drag on until 1988. Many on this side of the Atlantic doubt that the Reagan administration has any serious plan for dealing with the deployment crisis over the long haul. How can governments that are now willing to support the deployment -- like Helmut Kohl's in West Germany -- stick by their current policies for five years when the polls suggest that majorities of their populations oppose these new weapons? And what will be the damage to the alliance if they are forced to change policies before the deployment is complete?

Of course the alliance has survived any number of past crises and predictions of its imminent demise. But a number of European intellectuals point to important new divisions in political, military and economic spheres which -- combined with the pressures created by missile deployment -- do seem to make this round of Atlantic troubles more serious than earlier ones.

This does not mean the powerful political, cultural and economic ties that bind America and Western Europe are about to unravel. Nor is it news that West Europeans are once again dismayed by the policies of an American president. But we may be in for a qualitative change in Atlantic relationships, and considerably more European independence than we have experienced in the past.

When the North Atlantic Treaty Organization adopted its "two track" strategy in 1979 calling for arms control talks while preparing to deploy new missiles, nobody anticipated a serious deterioration in Soviet-American relations. Now the alliance is burdened by new anxieties over how to rebuild a dialogue and reach a modus vivendi with a hostile and suspicious leadership in the Kremlin.

On this point relatively few Europeans see eye-to-eye with the Reagan administration. Few Europeans are comfortable with President Reagan's ideological challenge to the Soviets. The widespread view on this side of the ocean is that detente with Moscow is imperative in the nuclear age.

In the wake of the Grenada invasion, even Reagan's closest allies in Europe, Margaret Thatcher in Britain and Kohl in West Germany, found it politically expedient to question his motives and practices. Both leaders have also distanced themselves from Reagan's confrontational approach toward Moscow and the tendency to see Soviet mischief as the source of turmoil in Central America and the Middle East. We can expect the post- deployment era to produce more independent European efforts to achieve more accommodating relations with the Soviet Union regardless of U.S. dismay.

The American public's response to Grenada troubled some European analysts even more than the anti-Soviet rationale for the invasion. What many Europeans perceived in the light of their nuclear debate as a naive and dangerous venture conducted without concern for negative repercussions among allies was applauded in the United States as a bold and successful display of American power.

"It is worrisome to see American and Europeans respond to the same event with exactly opposite emotions," said a senior European at NATO headquarters in Brussels.

The subsequent pique shown by the administration toward the uncomprehending views of allies over Grenada reflected an invidious cycle of distrust that some Europeans fear will intensify in the next five years of protracted missile deployment in the absence of an arms control agreement. As governments in Britain, West Germany, Italy, Belgium and the Netherlands wrestle with public discontent about nuclear weapons, the U.S. public may grow increasingly disenchanted with the spectacle of Europeans accusing Washington of imposing new missiles upon them when, in fact, their own leaders had approved deployment.

"I see a lot of strain and a lot of erosion in the alliance," said Martin Van Traa, foreign policy spokesman for the Dutch Socialist Party. "Europeans will talk more about their own interests, and then Americans will say, 'Let's leave them alone if they won't follow our line.'"

More than in any other European country, the political map of West Germany will be altered in important ways by the imminent arrival of Pershing II missiles. The opposition Social Democrats' decision to reject deployment has ruptured a hallowed consensus between the major parties on defense and security issues that played a key role in the country's remarkable postwar history of political stability. Even though Kohl's ruling center-right coalition maintains a comfortable majority in parliament, his government will continue to feel strong anti-nuclear pressures. One-half to two-thirds of the West German citizenry profess deep anxieties about deployment. That feeling coupled with disappointment over Kohl's failure to produce an economic upturn could mean further setbacks for Kohl in local elections.

In the streets, the Kohl government may be confronted with a new wave of terrorist actions by both right- and left-wing groups. Several top diplomats in Bonn have reported back to their capitals that they expect an upsurge in bombings against U.S. bases and munitions depots in West Germany.

In the long run, warns the Social Democrats' disarmament expert Egon Bahr, a prominent figure on the party's left, the alliance may face "nothing less than the destabilization of the Federal Republic of Germany" if new missiles are deployed in a climate of escalating East-West tensions. Young Germans, he says, will soon become disaffected if not embittered "by the experience that a clear majority which does not want the missiles in their country will not have their views respected by their government."

Since losing power last year, the Social Democrats have moved toward a more equidistant, if not neutralist, view of the superpowers. Already, there are mounting calls within the party to re-examine West Germany's commitments to NATO. For many young Germans, the vision of a reunified fatherland in a zone of nuclear disarmament has acquired the legitimacy of a noble crusade.

The political tide of West Germany's continuing nuclear debate will be greatly affected by developments in other European capitals. If the fragile ruling coalitions in Belgium and the Netherlands, which are due to station 48 cruise missiles apiece, fail to maintain a majority in favor of deployment over the next three years, this could trigger public demands for removal of the Pershings that Kohl would not be able to resist.

Belgium's center-right government survives by a weak consensus that could be shattered at any time by renewed unrest over the economy or by the country's perpetual linguistic quarrels. Opposition socialist politicians have joined the anti-nuclear campaign and vowed to block deployment if they are returned to power.

In the Netherlands, political analysts doubt that Premier Ruud F.M. Lubbers' center-right coalition will fulfill plans to station the cruise missiles in 1986. So far, the government has avoided declaring its outright support for deployment in the hope that an arms control deal will nullify the need for the missiles. Elections are also due in 1986; the anti- missile Socialist Party, the largest in parliament, may pick up enough support to form a new government that rejects deployment.

By that time, if Ronald Reagan has been re-elected, some Europeans believe that fundamental confidence in U.S. leadership of the Atlantic alliance will have been irreparably eroded. "I am afraid that the alliance will become swamped by a whole series of problems because we have been obsessed with rockets for so long," says Werner Holzer, editor in chief of the daily Frankfurter Rundschau. "There is increasingly little agreement, even on basics, because of our different assessments of Soviet motives. Europeans simply do not believe that blatant anti-communism can solve today's world problems."

Europeans may be increasingly tempted to explore alternatives to their dependency on U.S. nuclear and conventional forces. The goal of a Western European defense union has long been frustrated by enormous projected costs, suspicions about sovereignty and the reluctance -- at least by West German governments -- to give up the protection offered by the American nuclear umbrella.

In the past year, Paris and Bonn have begun consultations on nuclear planning because many French nuclear weapons are aimed at targets on German soil. Although French politicians such as the conservative Paris Mayor Jacques Chirac have encouraged a West German role in European nuclear strategy, politicians in Bonn remain skeptical. "We know the French will never give up their nuclear independence," says Bahr. "You can forget about any future European nuclear defense. It will remain a dream."

By 1990, however, French and British nuclear forces will be upgraded to the extent that their systems will be able to strike as many as 2,000 Soviet targets. Those modernization plans worry Soviet defense planners and help explain Moscow's insistence on incorporating French and British nuclear forces into the Geneva arms talks on intermediate nuclear missiles in Europe. If U.S. and European differences continue to grow over how to deal with the Soviet Union, the notion of developing a European nuclear deterrent from the basis of modernized French and British systems and reaching a separate arms control pact with the Soviet Union may no longer remain idle speculation.

"The erosion of these two key pillars of the alliance -- detente and nuclear defense guarantees -- have posed a unique historical juncture for Europe," argues Pierre Lellouche of France's Institute for International Relations in Paris. "There is no chance of turning back the clock to the days when we talked of an Atlantic partnership. Our only alternative now is to try and build on what will remain of NATO in the coming years."

Lellouche's institute has launched a long- term project to come up with the theoretical foundations of a European defense infrastructure building on the forces of France, Britain and West Germany. He contends that unlike previous efforts to form a West European defense union that "failed because there really was no need for it, people I meet now in Paris, Bonn and London realize that there is no other option for the future."

Other important factors underscore the trend toward future allied conflict. Europe's lingering recession, which has swelled unemployment lines and which so far has missed out on America's recovery, is likely to aggravate trade disputes with the United States.

The growing disparity between the U.S. and European economies caused by the microelectronics revolution is also accentuating political drift. Europe's technological weakness and slackened demand in heavy industries have forced companies and governments to look toward the relatively undeveloped Eastern bloc countries in search of dependable future markets. "This is what I call the real Finlandization, when key sectors of our economies increasingly come to rely on the Soviets," rt for says Lellouche. Leading West German businessmen say that Soviet bloc countries only account for about 5 per cent of German exports, but they admit that the proportion is likely to grow in sectors where there is high unemployment. "Chemical, machine tools and steel industries may find the Soviet market will become more important," says Dr. Franz Schoser, the executive manager of West Germany's Chamber of Industry and Commerce. "We do not believe that political tensions will affect economic trade with the East bloc. A more relevant factor is their ability to pay in hard currency, for which there is always a shortage."

But Schoser believes that the Soviets will be in a better position to pay when natural gas begins flowing to West European countries through the mammoth Siberian pipeline. "Our industry has a strong trading tradition with the East, especially the Soviet Union," Schoser said. "Nobody can ignore the market of a large neighbor and the U.S. government must understand that East-West business relations are something special for us."

A steadily rising proportion of European citizens who were born after World War II and have no memory of American aid in rebuilding their ravaged lands is emerging into positions of power and influence. Their image of the United States, in contrast to their parents', has been nourished over the past two decades by Vietnam, Watergate and a succession of flawed presidencies seen as too weak or too heavy-handed.

It is this generational change that could make the missile deployments a real turning point in the history of NATO.