PARIS, JULY 12 -- Faced with the prospect of reduced U.S. nuclear forces here, West European leaders are reviving the distant hope of an integrated European defense as a more independent guarantee of the continent's security.

Although the idea is decades old, proposals to improve European military cooperation have intensified sharply as the United States and the Soviet Union move toward agreement on eliminating their intermediate-range nuclear missiles in Europe. In some ways, the swiftness of this renaissance has provided a measure of West European uneasiness over the U.S.-Soviet bargaining and what it portends for Europe.

The U.S.-Soviet missile accord, which many Europeans assume will be completed by the end of the year, has been widely interpreted here as an important psychological step in a process that eventually could lead to a reduced U.S. military presence in Europe and less commitment to its defense.

Thus, appeals for greater European defense integration have blossomed across the continent since the United States called on NATO countries to approve the deal earlier this year despite reluctance in the major European capitals.

"The danger lies in the process getting started," said Jean-Pierre Bechter, secretary of the French Parliament's National Defense Committee. "With the signature of this treaty, we are entering a period at the end of which Europe must be ready to solve its own defense problems. Do you think 320 million Europeans can continue forever to ask 240 million Americans to defend us against 280 million Soviets?"

A number of European and U.S. strategists believe Moscow's long-term strategy is to proceed from missile reductions to troop reductions, which could further lessen U.S. ties to the continent.

Since Moscow has a large advantage in the number of conventional forces in Europe, such proposals may be relatively easy for the Soviets to make and have wide popular appeal in Western Europe, while posing a dilemma for NATO leaders.

Ideas for integrating European defenses traditionally have sounded good in politicians' speeches, but they have faced seemingly insurmountable problems that have prevented their realization.

France's refusal since 1966 to participate in NATO's integrated command, for example, makes cooperation difficult with this country. Similarly, Britain's special relationship with the United States, with sharing of nuclear technology and information, sets it apart from other European nations.

Rival national interests frequently have prevented practical, step-by-step defense cooperation even when it offered economic benefits. France, for example, recently decided to proceed alone with development of an advanced warplane after failing to reach agreement on a parallel European fighter project with Britain, West Germany, Italy and Spain.

Disputes over design have also delayed for several years a project to build a Franco-German combat helicopter even as the political and economic incentives for joint development mount.

French officials and commentators in particular have voiced fears that a reduction in U.S. nuclear commitment in West Germany, or an impression of it, could encourage ideas about neutrality and reunification with East Germany at the expense of the North Atlantic Treaty Organization. Any steps toward Franco-German military cooperation have been seen as a way to remove that possibility from the horizon.

"The Federal Republic is now entitled to feel abandoned by the United States, although constrained to toe the line in a U.S.-manipulated NATO that can no longer assure its defense," wrote former foreign minister Michel Jobert in a stiff version of these fears. "Hence the Germans' swing toward what they traditionally call their own way -- a swing uniting Social Democrats, Greens, the liberals of Hans-Dietrich Genscher and also, as we will see, Chancellor Helmut Kohl's Christian Democrats."

A strategic corollary to these concerns is that in an East-West crisis, West German authorities could be tempted to break ranks with the allies and seek conciliation on their own. This facet has been underlined by repeated West German objections that the prospective intermediate-range nuclear accord would leave NATO and Warsaw Pact ground forces within Europe armed with short-range weapons whose targets would lie in the two Germanys.

In addition, a high-ranking French official warned that recent Soviet arms initiatives have set in motion "a dangerous dynamic" that could lead to Soviet suggestions for further reductions and perhaps momentum toward a denuclearized Europe. This prospect has raised concern in Britain, France and the United States, whose arms control officials point to the Warsaw Pact's advantage in conventional and chemical weapons.

In West Germany, however, Kohl's government has favored following up on the prospective intermediate-range accord with talks on short-range weapons, or those under the 300-mile range. France and Britain, differing sharply with the Germans, have objected particularly to this idea because, officials here said, such negotiations could lead to Soviet demands for reductions in the French and British nuclear arsenals as well.

Against a background of these competing national concerns, Kohl offered the suggestion that has drawn the most public attention so far. He proposed June 19 that France and West Germany form a joint brigade of soldiers as a symbol of their determination to work together for European defense.

The idea of French and German young men training and living together, sharing languages and equipment, elicited favorable comment in both countries, which are scheduled to conduct joint military exercises next September.

French President Francois Mitterrand, while stopping short of rejecting the idea, has emphasized practical difficulties and historical obstacles to a joint brigade -- Germany and France have fought each other in three wars since 1870.

French Defense Minister Andre Giraud said last week that such a brigade would have to stay out of the NATO command structure and come under protection of French nuclear arms.

"The brigade is a real possibility that has mostly symbolic value, but symbols are important in this kind of thing," commented another senior French official.

Kohl's proposal came in reaction to a more sweeping idea from Alfred Dregger, a prominent West German Christian Democrat. He said Europe should create its own security arrangements, with France broadening its nuclear umbrella to cover West Germany. This suggestion reflected resentment among conservative West Germans about the Reagan administration's eagerness to conclude an agreement on all medium-range missiles in the face of European and particularly West German reservations. Despite NATO's acquiescence, a high French official said, reservations were strong in Britain, France and West Germany about the wisdom of removing shorter-range intermediate missiles.

The Socialist former prime minister of France, Laurent Fabius, at about the same time also urged France to think about extending their nuclear protection to West Germany as a part of increased defense integration. But other French and German officials quickly pointed out the difficulty of doing so while France remains outside the NATO command and West Germany remains a key element within it.

British Foreign Secretary Geoffrey Howe, joining the movement in favor of defense integration, called in a March 16 speech for increased "partnership" between France and Britain because, he said, Europe should recognize it no longer dominates U.S. thinking as much as in the past.

"I believe that we should recognize a greater responsibility on the part of Europeans for the defense of Western Europe -- in other words for a more truly equal second pillar of the alliance," Howe said.

Howe's comments, followed by a visit to France by British Defense Secretary George Younger, generated speculation that Britain also was seeking to increase the stature of the West European Union as a counterpart to the U.S.-dominated NATO structure.