After a decade of strengthening ties to the West, the communist nations of Eastern Europe are showing signs of growing concern about the cooling relationship between Moscow and Washington.

If the relationship between the two superpowers freezes into an updated version of the cold war, East European Communists say, the biggest losers will be the frargile countries caught in the middle: Poland, East Germany, Hungary, Czechoslovakia, Bulgaria and Romanina.

Despite all its limitations, detente has established a nework of agreements, understanding and human interchanges that would have been unthinkable for these countries a dozen years ago. And it has helped weave strong ties to the economies of Western Europe, a development that some see as strengthening the independence of the East European countries from a Soviet domination that once was nearly absolute.

This nightmare of a new cold war is seen as more of a real possibility than at any time since 1968, the year the Soviet Union led the Warsaw Pact invasion of Czechoslovakia.

The Reagan administration has come into office in Washington vowing to challenge Soviet military gains, and linking arms control, grain sales and East-West economic dealings to Soviet restraint in Poland.

While some in Eastern Europe believe it too early to make judgement about the Reagan policy on the Soviet Bloc, others say that raising tension between the two nations jeopardizes many of the gains of the last decade.

In a speech opening the 10th congress of the East German Communist Party last week, party leader Erich Honecker remarked that his country's relationship with West Germany "can't be separated from the overall international situation."

He went on the warn that a new nuclear arms race in Europe not only would prevent between the two German states, but also "threaten what has already been achieved."

Officials of the Reagan administration have pronounced detente a failure and described it as a one-way street that has lulled the West into relaxing its vigilance to the Soviet military threat while "reinforcing the prison wall" in Eastern Europe, as Defense Secretary Casper W. Weinberger recently put it.

Even detente's strongest defenders acknowlege that the policy of East-West relaxation has fallen far short of the hopes held out for it by Westerners in the early 1970s. Hundreds of critics of the Czechoslovak government are in prison; Soviet troops recently threatened Poland, and East Germany resembles a national prison with a heavily fortified border preventing the escape of its citizens and an ominipresent security police that suppresses dissidents and discourages contacts with foreigners.

But from the perspective of Berlin, a city surrounded by communist East Germany whose survival depends on harmonious East-West relations, the East Europeans' enormous stake in detente is evident.

Some experts suggest that without detente and the network of East-West economic and strategic links it created the Soviet Union long ago would have crushed the political process now unfolding in Poland.

But if detente has created dangers for Soviet control of East European governments, it has also provided the Soviet Union and its allies with access to Western technology and raw materials, such as grain, that have now become an essential underpinning of the communist econunist economies.

Thanks to extensive Western banking involvement with Poland, that country has been able to expand its debt to banks in West Germany, France, Britain and the United States to $23 billion -- an amount that has financed most of its industrial development in the last 10 years. Thus, Western banks now have a vital stake in political stability in Poland, along with the Soveit Union.

Union the aegis of detente, Romania and Hungary received most-favored-nation trade concessions in 1975 and 1978 respectively, making it easier for them to sell products to the United States.

Western credits have poured in to all the countries in the Soviet sphere and financed the importation of know-how and technology not available elswhere.

East Germany and Poland have become even more dependent on American grain than the Soviet Union and both rely on these feed grains to produce meat for their increasingly restive consumers.

It was detente that set the stage for the international recognition of East Germany and the estabilishment of a "special reltionship" between the two German states, which has proved extremely profitable for the East Germans. The West German government provided incentives to its industries to invest in the East in return for a substantial increase in contacts between families on both sides of the border.

For these and other reasons, the Soviet Union and its East European allies have sent clear signals in the last few months of their desire to keep detente alive in some form, regardless of the early skepticism shown by the Reagan administration.

The need to reopen negotiations between the two superpowers was stressed repeatedly last week by East European communist official in conversations iwth Western journalists in East Berlin to cover the party congress.

The reason cited most frequently was the foolhardiness of developing and deploying new weapons systems.

"If both sides go ahead with the new weapons systems the economic impact on our societies in East and West will practically as bad as if we had had a nuclear war," commented one Communists who added that the East European economies would be particularly hard hit by increased defense spending.

Addressing his party congress last week, Honecker noted almost sadly: "We aren't foolish enough to even dream about improving our relations with [West] Germany if relations between the U.S.S.R. and the U.S.A. are strained by the U.S.A.'s inexplicable policy of looking for confrontation."

American oifficials blame the Soviet Union for reviving tensions and cite the invasion of Afghanistan, recent military pressure on Poland, the onesided modernization of Soviet medium range missiles and alleged aid to terrorist organizations. Western officials in Euorpe say the Soviet clearly violated the "no threat" clause of the 1975 Helsinki agreement with recent maneuvers in and around Poland.

But East Europeans cite chapter and verse to show that the United States is to blame for the tensions, including the following examples.

The Reagan administration's failure to seek further clarification and explanation of Soviet President Leonin Brezhnev's Feb. 23 offer to negotiate a plan for military relaxation in Europe that would extend even deep into the Soviet Union. Administration officials have privately described the proposal as a public relations ploy aimed at winning over West Europeans and not a serious offer.

The administration's apparent reluctance to negotiate with the Soviet Union before deploying modern middle-range nuclear missiles in Western Europe in 1983. A North Atlantic Treaty Organization decision in late 1979 called for deployment of the weapons only in concert with negotiations aimed at reducing them.

"Slanderous" references by the American president to the Soviet Union -- a tactic that East European officials say underestimates the "psychological element" in dealing with the Soviets.

The U.S. Senate's failure to ratify the second strategic arms limitation agreement, in which Brezhnev had invested much of his political prestige.

Lack of reaction by the Carter administration to the Soviet Union's withdrawal of some troops and equipment from East Germany . Soviet officials were described as "furious" at Carter administration suggestions that the withdrawal had been a propaganda ploy.