At midday last Tuesday a high-powered group headed by the State Department's No. 3 official, Undersecretary Michael H. Armacost, attended a luncheon given by East German Ambassador Gerhard Herder. The occasion was the 10th anniversary of official U.S. relations with one of Eastern Europe's most orthodox communist regimes and, until recently, one of the most undeviating from Soviet direction.

A few hours earlier, at lunchtime in East Berlin, a similarly weighty delegation headed by the third-ranking official of the East German Foreign Ministry celebrated the same occasion at the residence of U.S. Ambassador Rozanne L. Ridgway.

In about three weeks, this unusually high level of contact is scheduled to be carried higher, as Secretary of State George P. Shultz confers in New York with East German Foreign Minister Oskar Fischer. The meeting will be the first between the chief diplomats of the two governments in six years.

Under serious study at the State Department is a journey by Shultz about three months from now, which would be an even more important symbol. If President Reagan is reelected, officials said, Shultz may travel to Yugoslavia, Romania and Hungary in December, his first trip behind the Iron Curtain as secretary of state.

The intensified official contact is part of the U.S. response to growing signs of political and ideological differences between Moscow and its buffer-zone Eastern European empire dominated by the Soviet Union since the end of World War II.

Eastern Europe's tugging at Moscow's leash was recently and dramatically illustrated by the dispute over the proposed trip of East German leader Erich Honecker to West Germany planned for late this month. Last Tuesday, the same day as the U.S. luncheons, Honecker bowed to Soviet pressure by postponing the trip, but this action came after more than five weeks of nearly unprecedented public jockeying between Moscow and East Berlin.

How the United States can take advantage of the trouble in the Soviet empire is a subject of much discussion in administration policy-making circles. Shultz, especially, is reported interested in the topic, seeing Eastern Europe as an area in the process of positive and inevitable change.

Much international attention was given to the Aug. 17 public statement of President Reagan, addressing Polish-Americans at the White House, that "we reject any interpretation of the 1945 Yalta agreement that suggests American consent for the division of Europe into spheres of influence" and to Shultz's statement in a Chicago speech Aug. 20 that "we will never accept the idea of a divided Europe."

The intensified contact with several Eastern European communist governments has been given little publicity -- last Tuesday's luncheon visit to the East German ambassador's residence, for example, was not announced -- partly because it cuts across the administration's "captive nations" ideology, and partly because of a belief that the less said, the better from the standpoint of the Eastern Europeans.

"Our policy is to gradually establish more healthy, normal relations with the Eastern European countries in the U.S. interest and in their interest," said a senior State Department official. He added, "The concept is that of differentiation among the various East European countries and between East Europe and the Soviet Union."

"We can accomplish this more by doing than by talking. To talk much about it is to endanger the process," the official said.

There is no belief at top levels of the State Department or, as far as could be learned, among top foreign policy officials elsewhere in the administration that anti-communist revolutions are impending in Eastern Europe. Several career officials made the point that showdowns such as that in East Germany in 1953, Hungary in 1956, Czechoslovakia in 1968 and Poland in 1981 were not in the U.S. interest because the cause of independence and dissent was set back by the eruptions. In every case the United States could wield only words of dismay while the Soviets and their agents wielded the guns.

In a New York Times editorial section article last Sunday, three prominent Democrats accused the Reagan administration of reviving John Foster Dulles' 1950s policy of seeking to "roll back" communism in Eastern Europe. Evidently referring to Reagan and Shultz's recent statements, W. Averell Harriman, Clark Clifford and Marshall D. Shulman said that whether this is "serious policy or merely campaign rhetoric is not clear."

The senior State Department official, one of the architects of policy in this area, said emphatically that "no rollback" is included in present U.S. policy, although "we don't accept the permanent division of Europe."

The seeming paradox is in keeping with the policy of earlier administrations. Over the years since World War II, administrations of both parties gradually have come to accept the Soviet domination of Eastern Europe as a fact, although none of them has accepted this domination as a matter of right.

Shultz, in his Aug. 20 address to the Veterans of Foreign Wars, suggested that any change for the better is likely to be gradual. "Time is not on the side of imperial domination," he said, but added, "We may not see freedom in Eastern Europe in our lifetime. Our children may not see it in theirs. But someday it will happen."

As seen by State Department policy-makers, two historical trends as well as several recent developments lay behind the recent divergence between Moscow and its Eastern European allies.

One trend is rising nationalism among Eastern European states, which for centuries were squeezed between Russia and Germany or, more recently, between Russia and the West. The resurgence of national identity has come with a decrease in Soviet control and an ebbing of communist ideology.

The other long-term trend is economic independence from the Soviet Union, which increasingly has less to offer Eastern European allies in aid or favorable trade. Soviet oil sales to its allies, for example, used to be below world market prices and thus amounted to a subsidy to Eastern Europe. Now the price is higher than that on world markets and amounts to a drain on Eastern Europe, according to State Department officials.

The way the world is moving economically, a U.S. official said, "the East European countries do not look east as a model for their development." More and more, they look west.

Recent and possibly temporary developments cited by the policy-makers are:

*Uncertainty and confusion in the Soviet leadership, which several officials cited as the most important factor behind the recent public displays of tension between Moscow and its Eastern European allies.

*U.S. nuclear missile deployments in Western Europe and Soviet counter-deployments in Eastern Europe. "The Soviets set out to scare West Europe and scared the East Europeans in the process. There's been a real blowback" in the east, including the rise of indigenous "peace movements" in several countries, an official said.

Such unpopular measures as the Soviet-directed boycott of the Los Angeles Olympics have put additional strain on relations with Moscow, several officials said.

The most significant new strains with Moscow, in the State Department view, are those in East Germany, which has been openly backed by an increasingly restive Hungary. Romania has been a maverick state, in foreign policy at least, for many years. What is termed "compelling evidence" of discord in Bulgaria, despite its seeming ideological compatibility with the Soviet Union, has aroused interest here.

Poland is still adjusting to the martial law crackdown of late 1981, and a wary U.S. administration is withholding consent to Polish membership in the International Monetary Fund until there is further and compelling evidence that the recently promised amnesty for political prisoners has been carried out.

Czechoslakia, on the other hand, is reported to have cemented ties with Moscow, though not without some misgivings about mixed signals from the Soviet leadership. Tiny Albania is still a province unto itself.

What Washington can do about this has been under study and discussion for several months in the administration. Mindful of its conservative constituency and intensely anti-communist nationality groups, the administration does not want to reward totalitarian communist rule in Eastern European countries. At the same time it seeks to encourage greater independence from Moscow and budding cooperation with the West in these same communist regimes.

East Germany, for example, remains a dictatorial communist state whose rule is anathema to Washington. Moreover, East German security operatives and advisers are scattered liberally around the Third World helping Marxist regimes suppress internal and external challenge.

Nonetheless, East German adherence to limited detente with West Germany, despite Soviet efforts to create a "new ice age" in Europe, is seen by the administration as worthy of encouragement. This point of view seems to have won the day.

East German leaders made it clear at the end of 1983 that they would work to preserve and even improve their ties with Bonn, despite the deployment of U.S. medium-range missiles in West Germany. Since then, there has been a series of little-publicized trips by senior U.S. officials to East Berlin, including:

*The late January visit of Undersecretary of Agriculture Daniel G. Amstutz, who declared East Germany a good credit risk and said private lenders in the United States would be encouraged to underwrite an increase in U.S. agricultural exports to that country. The exports had slumped in the previous two years.

*The February visit of Assistant Secretary of State Richard R. Burt, whose discussions in East Germany, as well as parallel talks in Bulgaria and Hungary on the same trip, reportedly centered on arms control. Burt's visit was given prominent attention on the front page of the Communist Party daily Neues Deutschland.

*The May visit of deputy assistant secretary of state Thomas M.T. Niles.

Like nearly all of the other Eastern European countries, East Germany has displayed persistent interest in increased trade with the United States, and especially in "most favored nation" trade benefits now denied all Iron Curtain countries except Romania and Hungary.

U.S. officials have spoken to the East Germans about "trade improvements" but have not held out the prospect of "most favored nation" status at present.

The view at the State Department is that the postponement of Honecker's trip to West Germany does not presage a general retreat from his regime's improved relationship with Bonn. To back up this view, officials cited "the very mild, open, positive line" of the East German official commentaries even after last Tuesday's postponement.

"The United States continues to support improvements in relations between the two German states as contributing to stability and peace in Europe, and would welcome a meeting between their leaders," the State Department said after Honecker's postponement. This backing for limited detente in Europe, even while U.S.-Soviet relations are frozen, is expected to continue and even grow in weeks to come.