The Reagan administration and Western Europe are having trouble communicating on an issue that governments on both sides of the Atlantic view as crucial: the eventual deployment of U.S.-built, medium-range Pershing II and cruise missiles in West Germany, Italy, England and possibly Belgium and the Netherlands.

A growing segment of public opinion in Europe, especially in West Germany, is worried about these missiles and other new U.S.-built neutron weapons because they fear such arms could make war in Europe more rather than less likely.

The Soviet Union, which has hundreds of medium-range missiles pointed at West European targets, has nevertheless been able to exploit these fears among the population in the West and thus create additional problems for NATO governments and for political cohesion within the alliance.

The Reagan administration, in effect, acknowledged that Moscow was making public relations inroads when it dispatched Secretary of State Alexander M. Haig earlier this month to West Berlin to give allied populations a pep talk.

Haig, however, spoke mostly about the virtues of democracy in comparison with the repression of Soviet-style government and, while he was eloquent, that is not what really worries the Europeans.

French, British and West German political-military specialists visiting this country recently maintained that the U.S. administration has never successfully explained how these weapons would be used or what the strategy is behind them, other than to picture them as a balance to some 250 new Soviet SS20 multiple-warhead missiles already fielded.

What troubles the Europeans, these specialists say, is a combination of factors. These include increased talk of so-called "limited" nuclear wars that began in the Carter administration; a perception that the Reagan administration is not very interested in arms control; extremely harsh language directed at Moscow by Reagan, and the fact that the most-talked about new U.S. weapons--the Pershing, cruise and neutron arms--are all aimed at fighting on a European battlefield.

What these conjure in some European minds is a picture of an America poking its finger at Russia while operating under a doctrine and deploying new weapons that suggest if a battle comes, it will News Analysis News Analysis be limited to a fight in central Europe without exposing the U.S. homeland.

Thus, some Europeans see these new weapons as "decoupling" the traditional nuclear umbrella the United States has held over Europe since World War II--a pledge to send long-range bombers and missiles from this country toward the Soviet Union if necessary to defend Europe or to deter an attack in the first place.

What needs to be explained by American officials to allied populations, the specialists say, is the relationship between these new U.S. weapons and the continued ability to deter the Soviets.

For one thing, the difference between the new Pershing and cruise missiles and the thousands of older short-range atomic weapons that have been based in Europe for decades is that the new 1,500-mile range weapons can reach the Soviet homeland, rather than fall on East or West Germany. Thus the Soviets, if they were contemplating an attack in central Europe, could no longer be sure the battle would take place on somebody else's soil.

Theoretically, at least, this is supposed to deter the Soviets from trying to exploit a current imbalance in East-West nuclear forces in Europe. The Pershings, in particular, present a new threat because they would hit their targets within five minutes or so, giving the Soviets virtually no warning time.

The new weapons therefore are meant to close a gap in deterrence because they are supposed to give NATO a chance to strike the Soviet homeland from Europe just as the Soviets have for years had the ability to strike directly at European targets.

Officially, they are also meant to strengthen the "coupling" effect since the weapons will be under U.S. control and the Russians, once hit by an American atomic warhead, may not care much whether it comes from West Germany or South Dakota.

Whether any of this would make those Europeans who are already nervous any less nervous remains to be seen. But the European specialists feel it must at least be explained better than it has been and that it must be done by Americans.

Some European leaders, especially West German Chancellor Helmut Schmidt, have tried to explain some of the details publicly. But it is hard for a German leader to talk openly about missiles from bases in his country striking the Soviet Union.