East German's efforts to rid itself of critics by forcing them into exile has now produced a cultural migration of significant proportions.

Within the past 15 months or so, more than 20 authors, poets, musicians and theater personalities - a number of them well known beyond East Germany as well as inside it - have been leaving their homeland and crossing into West Germany.

That, is probably more than the total number of such dissidents dealt with that way over the last 15 years.

Although the use of forced exile is growing throughout East Europe, East Germany may now be its most successful practitioner, a situation that has been dramatized in recent days.

In late August, 42-year-old lyricist Sarah Kirsch, viewed by many as perhaps the best contemporary poet in East Germany, crossed the wall to the Western sector of Berlin.

For months she had complained about the same things other artists have been plagued with - harassment, pressure, inability to work or get published.

When she finally applied in July to leave the country - which lets virtually no one except old-age pensioners out - the authorities quickly approved her exit permit.

Just a few days earlier, author Juergen Fuchs and two musicians, Gerulf Pannach and Christian Kunert, who had been part of a irreverent, once popular but now banned rock band, were released from East German jails and allowed to choose exile as a condition of their release.

With them, in what was probably the first group expulsion from the East was German-language Prof. Hellmuth Nitsche, who had at one point written to President Carter in an effort to call attention to human-rights violations, and Dr. Karl-Heinz Nitschke, a physician.

Nitschke was arrested last fall after collecting some 80 signatures on a petition and sending them to the United Nations with the demand that East Germany live up to the obligations of the U.N. Declaration of Human Rights.

The petition Nitschke circulated in Riesa was the first real sign of unrest surfacing in East Germany last year. It was followed by the revelation that as many as 100,000 East Germans, citing provisions of the 1975 Helsinki agreements on European security, have asked for persmission to leave - a request not likely to be granted, but involving considerable risk to their future in East Germany.

Shortly after that, lat January, some 240 Czechoslovak citizens signed the Charter 77 human-rights manifesto, which has had a dramatic impact in East and West as a philosophical challenge to hard-line Communist governments.

The East Germans have been careful not to crack down on their dissenters as hard as the Prague government, whose reputation has suffered even among outside Communist parties.

Yet specialist here say that East Berlin is worried about the Czechoslovak example. Several of the key Charter 77 signers were playwrights and writers, and the East Germans seem to be aiming at exiling or isolating anyone likely to attract many followers or form any organized dissident group, especially if workers are involved as well as intellectuals.

The regime may also be trying to force most of the critics out and to calm things further before the Belgrade conference to review implementation of the Helsinki accords begins in October.

The regime also seems willing to accept some damage to its image in the West in return for the prospect of removing sources of dissent.

Since West German television is seen throughout 80 per cent of East Germany, many of the exiles may again be seen or heard by East Germany viewers. But like others in the Communist bloc; East German officials believe that many writers lose both their appeal and their inspiration when they lose their homeland.

Manfred Krug, East Germany's top ballad and jazz singer and a popular film star, said when he was forced into exile in June that leaving East Germany nevertheless was like "an amputation," even though it had become virtually impossible for him to continue his career there.

On the other hand, Krug said, he tried to see it less as exile than "as a move from Germany to Germany" - reflecting the important and mitigating different between East Germans' being exile to West Germany, with its common language and heritage, and a Russian, for example, winding up in Sweden.

West German specialists believe that only those with the strongest Communist backgrounds, who need a distinct left-wing environment to motivate them, will be unable to continue their work here.

The exodus of writers and performers has put an end to the policy of a "cautious liberalization" of culture that East German Communist party chief Erich Honecker promised when he took power in 1971. "There can be no taboos in the fields of arts and literature," he said at the time, "so long as one's starting point is basically Socialist."

The pressure tactics have also hurt East Germany culturally.

"I feel very sad that we have lost so many talented people," said East Germany's best-known writer, novelist Stefan Heym, in a recent interview. "It makes life here much poorer."

Heym is such an internationally known maverick Communist and critic that so far the East Berlin goverment has not brought pressure on him to leave. "Anyone who leaves us can no longer help us create the kind of humane socialism that will enable us to tear down the wall," Heym said.

The beginning of the exile wave goes back to last November when the Marxist singer-poet Wolf Biermann, a sharp critic of the way socialism is practiced in East Germany, was refused permission to return from an unprecedented singing tour in West Germany.

Many of those now being exile were among the dozen prominent East German intellectuals who first protested Biermann's exclusion. Sarah Kirsch, a former Communist Party member, had been among them.

In the aftermath of the Biermann affair, author Thomas Brasch, 31, whose father served as deputy culture minister, was allowed to leave, along with Kathrina Thalbach, a young and already acclaimed actress. then singer Nina Hagen was also let out.

Actresses Dagmar Graf and Eva Marie Hagn, writers Siegmar Faust and Bernd Jentzsch, the widely acclaimed lyric poet Reiner Kunze, composer Tilo Medek, musician Klaus Renft, Berlin Ensemble director Einar Schleff and comedian Eberhard Cohrs have all, in one way or another, been forced into exile.

The next to be forced out may be Jurek Becker, who wrote the screen play for a widely acclaimed East Germany film, "Jacob the Liar."

Becker, who also protested Biermann's expulsion, has been black listed and banned from lecturing and publishing.

Like Sarah Kirsch, Becker is Jewish, and there have been reports that overtones of anti-Semitism have crept into party dialogues over the situation.

Friends of Becker's here, say he wants to stay in East Germany despite the harassment.

"I can say that despite some complaints, I was always happy in East Germany," Becker said in a recent interview with the West Germany news-magazine Der Speigel.

"I always had the feeling of participating in something I think is important. I want to remain here as somebody who can publish what he writes.

"But if it is matter of keeping my mouth shut," the pragmatic author added, "then I prefer to keep it shut in the Bahamas."