East Germany stationed armed security police in front of the West German liaison office in East Berlin today in a dramatic new move by the Communist government to stop its own citizens from applying for permission to leave for the West.

It is the first time East Berlin has actually denied its citizens entrance to the building and the move seemed clearly to be part of a spreading crackdown against a portion of the population that has been showing an unusual willingness to demand more personal freedom and the right to emigrate.

Bonn's representative to East Germany said it was the most serious hindrance to the mission's work since it was set up in 1974.

According to Western estimates, some 100,000 East Germans, beginning roughly last spring, have turned up at the West German mission in the Communist sector of Berlin to inquire about emigration.

The growing number of applicants - only a handful of whom were actually allowed to leave last year - has become a serious and embarrassing problem for the ruling Socialist Unity [Communist Party]

U.S. and other Western officials also voiced concern privately over the move since it fell into a pattern that suggets a hardening of East German policies toward West Germany, in particular.

Western governments responsible fro Berlin under the Four Power accords issued a statement last week criticizing a new East German visa requirement to enter East Berlin and today lodged a protest with the Soviet Union. The visa requirement viewed as a "unilateral" East German attempt to have East Berlin considered part of the East Germany.

In Bonn, the West German government lodged a swift and strong complaint against today's action, describing it as "very serious."

West Germany's representative in East Berlin claimed today's action was "not reconcilable" with the provisions of the 1975 Helsinki agreement on European Security and Cooperation in which 35 nations, including East Germany, pledged to improve human contracts between East and West and to allow greater freedom of movement.

That portion of the Helsinki accords, plus U.N. resolutions on human rights, are being cities by many of the East Germans trying to get out.

Until today, East Germans couldgo unimpeded to the West German mission in East Berlin.

In recent weeks, however, the East German government began trying to deter people from even applying for emigration. There were scores of reports about persons losing jobs after their applications had started to be processed. Last month, there were also sporadic "identification checks" of people leaving the West German offices, allegedly to make sure the West was not helping any "criminals" get out.

The East German government said today's move comes under a 1963 order that requires East German citizens who want to contact foreign missions to get permission first from the East German Foreign Ministry.

Two armed guards were posted in front of the West German mission this morning. Three others patrolled the front of the building. Across the street were other plainclothes security officials. Persons approaching the building were stopped if they were East Germans and told they needed permission to enter.

Diplomatic sources elsewhere in East Berlin said no restrictions or identification requirements were placed on other embassies there, although there has always been a guard on duty at many embassy entrances.

West Germans in East Berlin and other foreigners were being allowed to enter the West Germans mission unimpeded.

For the past 15 years, ever since the Berlin Wall went up, sealing in East Germany's 17 million people, the only persons a llowed to migrate westward have been pensioners over 60 and some family hardship cases.

Those policies have never changed and how says one Western official, "They are trying once and for all to stop this new idea that you get out because of the Helsinki accords."

The latest East German actions come against a backdrop of growing restiveness, including protests by dissident intellectuals in several East European countries, including Poland adn Czechoslovakia, and fit into a pattern of moves that several governments are now taking to try and put down this dissidence.

The biggest rub for the East German government is that the applicants are asking to go to West Germany.

In the view of many experienced observers here, the crackdown is harshest when West Germany is used as a platform for dissident views or as a destination for emigration.

Although the stationing of guards serves as a clear warning to citizens that they cannot even apply any more.