Rarely has a group of leaders met after having so completely achieved its objectives as did the participants at the NATO summit in London. With communism collapsing as an operational philosophy, even in the Soviet Union, the Warsaw Pact disintegrated and Germany unifying, the Cold War had clearly ended. All of this has now further culminated in Mikhail Gorbachev's agreement to the membership of a unified Germany in NATO.

In the euphoria of these events, a word of caution may seem captious. But I cannot avoid the uneasy feeling that while the West is celebrating, its underlying cohesion is being hollowed out.

It is true that existing institutions must be changed in light of the dramatic developments of the past year.

But contrary to conventional wisdom, and at the risk of causing pain to some valued friends, I have come to the reluctant conclusion that progress toward German unification has been more rapid than progress toward solutions of the underlying structural problems. Indeed, there is a danger in the London communique' issued by NATO that the world it envisages will be safe only on the assumption of a permanent Soviet weakness, that over time Germany will be torn between its ties to the West and its temptations toward the East and that America may become progressively irrelevant to the evolution of Europe.

One reason for the allies' avoidance of these trends is the degree to which Gorbachev has mesmerized Western public opinion.

Gorbachev will undoubtedly go down in history as a seminal figure who changed forever the destiny of his people. But do we really understand what is required to help him through the wrenching process underway in Moscow? And are Western leaders helping him in the long run by choosing sides in the arcane power struggle taking place in Moscow? Does explaining so many of the provisions of the summit communique' as ''face-savers'' without much substance help or hurt? If they are really empty, will Gorbachev's opponents be fooled? And will not Gorbachev, who is after all an experienced statesman, seek to give operational meaning to words intended for public effect? In so fluid a situation, is not the only sound course for the Alliance to put forward a program sustainable on its merit by any foreseeable Soviet leader?

There was a tendency in London to seek to co-opt traditional critics and to reassure the Soviet leadership by falling in with the premises of 30 years of anti-NATO propaganda. Several allied briefers argued that the communique' would enable Gorbachev to tell his colleagues that NATO no longer posed a threat to the Soviet Union.

But in what way was NATO ever a threat to the Soviet Union? The end of the Cold War does not require a denial of a history of 40 years of crises, repressions and documented assistance to global terrorism. What it does require is an answer to two questions: Toward what threat and with what means is the alliance to be directed? And what is to be the political role of NATO?

With respect to security, the London communique' announced drastic reductions in conventional weapons and a new nuclear strategy. But since the communique' did not define to what Soviet threat these changes are to be geared, the various measures in the conventional field -- the reduction of forces, the ceiling on German forces, the lowering of readiness and a greater reliance on reinforcements -- are hard to assess.

In any event, the domestic turmoil in the Soviet Union makes a conventional attack highly unlikely for the foreseeable future. But even after a strategic arms agreement, the Soviet Union will retain a nuclear arsenal 10 times larger than the combined British and French nuclear forces, and this will pose the most plausible Soviet threat.

In this context, the new NATO nuclear doctrine is puzzling. The London summit announced the modification of the doctrine of flexible response, the readiness to withdraw all short-range nuclear weapons from the continent and a commitment to use nuclear weapons only as a last resort.

But why has flexible response suddenly become so controversial? All it ever asserted was that NATO would use the minimum force to repel aggression. Therefore, even in nuclear war a series of firebreaks would be attempted before the ultimate recourse. In what way does the new doctrine differ? Indeed, what is the new doctrine? What does last resort mean? Whose last resort? Germany's? The United States'? What change does Gorbachev see in the new doctrine, since he mentioned it as one of the reasons for shifting his position on German membership in NATO? Will any nuclear weapons remain under the direct control of the NATO commander?

We are in fact in the midst of a process of denuclearizing Europe -- largely driven by German domestic politics -- which has shifted from the withdrawal of intermediate-range missiles to the withdrawal of medium-range weapons and now to the nuclear artillery. After all short-range nuclear weapons have been eliminated, only nuclear bombs on tactical aircraft will remain. How soon before they too come under attack? Indeed, what is the rationale for maintaining them?

Moreover, denuclearization is unlikely to be the end of the story. If Germany is serious about banishing the risk of nuclear war from its soil, it will come to interpret the doctrine of last resort as meaning no first use of nuclear weapons. Then America will be asked to risk nuclear devastation on behalf of a country not prepared to run such risks for itself. Is that not precisely the definition of the decoupling of the United States from Europe, which 40 years of NATO policy has sought to avoid and of Soviet policy to achieve? Are we then back to the doctrine of massive retaliation, from which every American administration since the 1950s has sought to escape because of the lack of credibility of the choice it posed between suicide and surrender? Would the American people in their post-Cold War mood support such a policy?

In any event, Britain and France have dissociated themselves from the new nuclear concept. Other Europeans seem confused, oscillating between seeing in it nothing significantly new and equating it with no first use of nuclear weapons. Is such ambiguity helpful for deterrence? Does it not accelerate the delegitimization of nuclear weapons in the eyes of European and American publics? Does it mask an underlying assumption that there is nothing to worry about because the Soviet Union will remain permanently weak -- a curious position for Allied leaders who keep proclaiming their commitment to the success of a perestroika designed to make the Soviet Union strong?

What about the enlarged political role for NATO? Only two concrete political proposals relevant to the Alliance were made: that Gorbachev address the NATO council and that liaison missions from the Soviet Union and other East European countries be established at the NATO council.

What is the purpose of either measure? Since Stalin's day, the Soviet Union has sought to make NATO irrelevant by offering to join it. What exactly does the Alliance expect from a meeting with the Soviet leader other than a recycling of the oft-repeated statements that NATO is unnecessary, if not dangerous? Moreover, the meeting is patently redundant, since Gorbachev will already be attending -- at more or less the same time -- the summit of the Conference on Security and Cooperation in Europe (CSCE), where he will also meet all of NATO's leaders. How long will democratic public opinion support an alliance that calls its former adversary a ''partner in security''?

And what are these liaison missions supposed to accomplish? To whom are they accredited? If to the NATO Council, can Soviet observers attend its sessions? Even if not, the missions will either become part of the Brussels decision-making process or duplicate the present role of Soviet missions in allied capitals. Significantly, the communique' is silent on a political role for NATO that would be truly new: some mechanism for dealing with conflicts outside the NATO area.

The failure to define a serious political role for NATO becomes the more unsettling when compared with the relative precision of the communique' regarding the role of the CSCE. Though the communique' refers to that conference as subsidiary, in practice that is lip service. The European Security Conference -- comprising 35 states from Europe and North America -- has been touted for years both by the Soviets and by NATO's opponents as an alternative to the Atlantic Alliance. The proposed CSCE summit conference includes conflict prevention and conciliation of disputes among member states in its agenda together with a permanent secretariat. This edges the conference into the field of security where the veto of each member equates the threat with the remedy.

The increasing emphasis on nationalism will be encouraged by the proliferation of summits. With in a six-month period there will have been two NATO summits, a European Security Conference, an economic summit and the regular monthly summits of the European Community. Since more or less the same leaders meet under different labels almost monthly, the distinctiveness of any one institution is bound to erode. A kind of Gresham's Law threatens to begin operating whereby the more inclusive conference -- that on European Security -- comes to dominate all the others. This is all the more true because it is at the CSCE that the Soviets will be present and the opportunity for publicity will be greatest.

This maze of institutions will enable countries to shop among the various institutions for the one that best serves their interests. Summits will come to ratify national decisions rather than shaping them by consensus. For instance, Germany announced a major aid program to the Soviet Union shortly before the NATO summit; Japan proclaimed an abrogation of sanctions against China just before the economic summit; and the European Community accepted a CSCE summit about the same time -- despite the known coolness of the United States to all these schemes and before any consultation at the various summits. Even the four-power foreign ministers' meetings on the unification of Germany have been reduced to a forum for ratifying decisions previously made bilaterally between West Germany and the Soviet Union.

One explanation for this state of affairs is the unusual complexity of the contemporary international environment. Every leader has to consider not only the substance of the subject at hand but also his domestic constituency as well as the constituencies of all his opposite numbers. And somebody is always up for reelection. In the process, drafting a communique' may become its own purpose; procedure and domestic politics inadvertently overwhelm long-range thinking.

This is why one of the most dramatic results of the NATO summit was Germany's dominant role. No Western leader has a more immediate problem than Chancellor Helmut Kohl, who, with amazing single-mindedness and skill, is completing the extraordinary tour de force of unifying Germany and winning a national election in the same year. His imperatives are clear: to reassure the Soviets, to pay both fiscally and politically what is necessary to culminate his masterful diplomacy.

From his perspective, this makes sense. Kohl will deal with his promissory notes after having seized the perhaps never to recur moment for unification. What is less clear is the American reluctance to introduce a broader perspective -- and I say this as a friend of Chancellor Kohl of long standing who urged the inevitability of German unification while many in Washington were still hesitant lest such a course threaten Gorbachev's survival. Be that as it may, there is now a real danger that Germany's membership in NATO will be purchased by draining the Alliance of military substance and subsuming its political role in the European Security Conference. If present trends continue, NATO will at best become a unilateral American nuclear guarantee enabling individual European nations, especially Germany, to pursue their national goals in the East on their own; at worst, political pressures in America could undermine that guarantee.

The Western leaders still have every opportunity to define a genuinely new relationship with the Soviet Union, to integrate Germany into a larger system and to strengthen the links between America and Europe. But they must raise their sights to a vision of the world they are striving for. To do so they must come up with a new concept of security, and they must be able to devise new political objectives. Maybe the problem is insoluble. But if it is, the London summit will be remembered not for the renewal of the Western Alliance but for the beginning of its demise.