East Germany appears to be engaged in a widening crackdown on political dissidents.

Robert Havemann, a former East German professor who has been under house arrest for 2 1/2 years for criticism of the state, now is under investigation for alleged foreign currency violations and has been put in even tighter isolation, according to reports from East Berlin.

Havemann, 69, is a Marxist who was expelled from the Communist Party and his Humboldt University chemistry teaching position in 1964 when his views began to stray from the party line. He has since become the most internationally prominent political critic of the East German government.

Stefan Heym, probably East Germany's most prominent author, also complained this week of new harassment linked to foreign exchange regulations.

Heym, in a statement issued to British correspondents this week, claimed that East Germany was now coupling its copyright laws with the foreign exchange regulations so that any author whose work is published in the West without permission of the East German government was committed an offense and could be punished with up to 10 years in jail.

Heym said the new rules are an attempt to silence authors. "They talk of foreign exchange, but in reality it is freedom of speech that is at stake," he said.

Heym, 66, is a German-born Jew who fled Hitler's Germany, served in the U.S. Army during World War II and then returned to a post-war East Germany communism that he believed would work. He is so well known internationally as author and maverick Marxist that, while occasionally a harsh critic of the type of socialism that East Germany practices, he was largely been left alone by the authorities.

Yet, last week, before making the claims about the new foreign currency situation, he also told reporters that he had been barred from accepting a lecture invitation in West Germany and complained that secret service agents were trailing his wife.

Heym's latest book, "Collin", which criticizes the East German security apparutus, was recently published in the West. East German authors, many of whom had been exiled to the West in previous periods of dissent and crackdown, are generally paid in Western currency by their Western publishers.

Heym compared the new restrictions to a form of "McCarthyism."

Two weeks ago, East German authorities also shut down the show at the country's most famous political cabaret, the Peppermill in Leipzig, the first time in 15 years that such a move was made against one of the few places where political satire is allowed in the tightly controlled state.

Last week, the government alos announced new restrictions on foreign correspondents working in East Germany. They ban interviews others than those officially approved.

The restrictions are aimed especially at West Germany reporters based in East Germany who frequently interview East Germans willing to speak out on various issues. Later, East Germans can see those interviews on their television sets because West German television can be picked up in most of the East.

The Bonn government has attacked the restrictions on journals as a violation of the Helsinki agreements on European cooperation and this week West German Chancellor Helmut Schmidt described that East German move as a sign of the 'weakness of its leadership', a description that apparently rankled East German leaders.