Leftists Find Good News, Bad News in East-West Thaw : Radicals: Foreign policy critics worry that loss of the Soviet Union as the enemy also means loss of a powerful deterrent to U.S. intervention.

These are days of reassessment for the radical left in the United States. The compass points in a familiar direction, but many of the old landmarks are gone.

The collapse of communism in Eastern Europe has been a bittersweet turning point for American radicals, who have often defined themselves in European terms.

“It sort of forces American radicals back to step one, or back to their own deepest instincts,” said Paul Buhle, an editor of the Encyclopedia of the American Left. “They can’t borrow from Europe.”

Left-wing intellectuals and political leaders in this country are virtually unanimous in their support for democracy in Eastern Europe, and most have rejoiced in the passing of what Socialist Irving Howe calls “the historical tragedy called Stalinism.”

Still, they recognize that the changes have saddled the left with something of an image problem.

“It’s perfectly clear that, for a time, we will suffer a backlash,” said Howe. “One must be honest about this. There is no question that what happened represents at least a partial triumph of capitalism.”

Howe’s point is by no means universally accepted, as little is on the left. The radical left spans an ideological continent, from the liberal side of the Democratic Party to fringe groups such as the Revolutionary Communist Party and the Progressive Labor Party. Skirmishes within that territory--between Socialists and Communists, say--can be as fierce as those between the left and the right.

David Plotke, political science professor at Yale University, said of the term socialism : “If there’s a group that includes Willy Brandt, Gorbachev, the Italian Communist Party and Pol Pot, that’s not a very thick term.”

There are some points on which most American leftists would agree, however. One is that the changes in Eastern Europe should help their cause, because they remove the stigma of a Red Menace.

“That’s a great burden lifted from us,” said David McReynolds, a leader in the Socialist Party U.S.A. who ran for President in 1980 and, at 60, can remember the smear era of Sen. Joseph McCarthy.

The perception of a global communist threat has long plagued the left, communist and non-communist alike. Now, McReynolds said: “No matter what happens, the left no longer has to look over its shoulder and apologize for the Soviet Union.”

That is not to say there is no nostalgia for the bad old days. Critics of U.S. foreign policy worry about how the United States will react to the demise of the Warsaw Pact.

“Whatever one thinks of the Soviet Union--good, bad or indifferent--over the years, it has served as a deterrent to U.S. force,” said linguist Noam Chomsky, a professor at the Massachusetts Institute of Technology. “So, that deterrent effect is gone.”

Few leftist leaders believe the changes in Eastern Europe will have a significant effect on the memberships of left-wing organizations in this country. Most of them have been shrinking for decades.

Carole Marks of the Communist Party U.S.A. said that the party has perhaps 25,000 members, and is optimistic about future growth. Other sources said that Marks’ figures sounded far too high; they also laughed off the Communist Party’s importance to the modern American left.

“The Communist Party is in a very odd position,” McReynolds said. “They’ve had a sort of franchise from Moscow to run things here. That’s breaking down. The Soviet Union doesn’t give a tinker’s damn about what’s happening to the communist parties around the world. . . . They’re in a position that you really have to have a sense of humor to appreciate.”

McReynolds, Howe and other leftist leaders openly acknowledged that their organizations (Howe is affiliated with the Democratic Socialists of America) are minor league players on the political scene. The future, they said, probably belongs to some new movement that may not yet exist.

Mark Raskin, a former aide to President John F. Kennedy who is now co-director of the Institute for Policy Studies, a liberal Washington think tank, is editing a special issue of The Nation magazine that will assess the state of the left.

On the one hand, he said: “There is nothing to suggest that capitalism is anything but a very unstable system.” On the other hand: “There is nothing to suggest that state socialism is anything but a collapsed system.”

What’s needed, Raskin said, “is something quite new and different.”

Whatever that something is, Raskin believes, it probably will involve strong commitments to improving the environment and promoting civil liberties. Others said that such a movement would need to address the interests of racial minorities, homosexuals and women.

Many on the left said that American radicals can assist the emerging democratic movements of Eastern Europe.