Western diplomats are increasingly concerned that after a decade of tranquility, East Germany and its patron, the Soviet Union, once again are trying to expand communist control over Berlin.

After nearly two weeks of wrangling over passport controls, East and West are at an impasse, with the United States, Britain and France resisting what they say they believe is an East German effort to chip away at allied rights in the divided city.

At issue is the drive started by East Germany on May 26 to force diplomats, military personnel and dependents from NATO countries other than the United States, Britain and France to show their passports when crossing between West and East Berlin. It justified the action as a response to U.S. demands that East Germany curb the movement of Libyan diplomats from East Berlin into the West following the April 5 bombing of a nightclub patronized by American soldiers.

Widespread compliance with this demand would enable East Germany to argue that these countries recognize the crossing points as an international border. This recognition would strengthen the communist bloc's contention that East Berlin is the capital of East Germany.

"The East Germans clearly are hoping that the resulting hardships will cause attrition in the West's solidarity," one U.S. official said. "They think that if they continue to stonewall, they can make the allies blink first. We're still not sure how serious they are about keeping it up, but we're determined to maintain a measured response that will demonstrate that the old 'salami tactics' of cutting into allied rights a slice at a time won't succeed."

U.S. officials said yesterday that, despite some scattered instances of compliance, the NATO governments so far have tried to rebuff the maneuver by taking a circuitous route out of the city limits into East Germany and then reentering Berlin proper through East German border points. The allied position is that Berlin is under the control of the four principal World War II victors and that East Germany has no authority there.

But officials also acknowledged that East Germany's refusal to back down is making it difficult for the NATO countries to conduct their business in Berlin; some western diplomats warned that a continued impasse could erode NATO unity and cause some governments to seek a compromise meeting some of the East German demands.

These sources said that the situation is especially awkward for Chancellor Helmut Kohl's West German government, which fears that renewed East-West confrontation over Berlin could damage its policy of broadening ties with East Germany. Signs have already emerged that elements in the Bonn government are pressing Kohl to urge the allies toward flexibility.

The history of the dispute goes back to 1945, when the four wartime allies divided Germany into four zones of occupation. Berlin, located inside the former Soviet zone, was given special status as being under four-power control and was similarly divided into four zones.

When the Soviets created East Germany out of their zone, they sought to establish East Berlin as the new country's capital. But that claim has never been recognized by the three western allies, which have maintained their zones as a western enclave 110 miles inside the communist east. Although West Berlin has a limited association with West Germany, the allies have never wavered from their insistence that the entire city must remain under four-power control until a formal agreement resolves all the problems of Germany's postwar division.

After 25 years of East German and Soviet attempts to force the allies out of the city, the Berlin situation lapsed into relative quiescence. In the May 26 passport decree, the East Germans initially tried to impose the measures against all western diplomats. But within hours the threat of a major confrontation with the allies forced East Germany to back away from the contention that U.S., British and French personnel were subject to the new rules.