Moscow's biennial book fair opens Tuesday, with American publishers taking part for the first time since the imposition of a boycott after the 1979 Soviet invasion of Afghanistan.

The fact that American publishers have returned to the fair in the face of international uncertainty about the fate of writers imprisoned or exiled in the Soviet Union reflects anxiousness about how writers and artists will fare under the new Soviet leadership, according to both western observers and Soviets speaking privately.

In contrast to 1979, none of the books brought by the U.S. publishers were barred this year by Soviet authorities. That year, several, including books by Alexander Solzhenitsyn, were confiscated.

But this year the U.S. exhibit, entitled "America Through Americans' Eyes," includes no books by Soviet emigres in the United States. The 313 to be displayed include Jonathan Schell's "The Fate of the Earth" and the Union of the Concerned Scientists' "The Fallacy of Star Wars," as well as the Sears Roebuck catalogue and the 1984 Olympics handbook, with pages on the Soviet boycott of the Los Angeles games.

The Moscow Book Fair is both a showcase for the world's contemporary literature and a market for writers, publishers, and translators.

In a country of avid readers, foreign books of direct interest to the Soviets, such as Strobe Talbott's "Deadly Gambits," are known only to an elite few. Classics such as "Anna Karenina" are rarely seen on bookshelves, and new works by contemporary Soviet writers sell out in days. Accordingly, the book fair is practically a week-long holiday. Soviets come from as far away as the Black Sea and Soviet Georgia to view the books.

A Soviet official, speaking at a press conference held to discuss the fair, said today that American publishers' contracts with Soviet authors are dwindling, and the United States has imported from the Soviet Union only a third the number of books it has exported to this country.

"Maybe there are attempts to create artificial barriers" between American readers and Soviet writers, the official said.

But a spokesman for the Association of American Publishers responded that available books by contemporary Soviet writers are not marketable in the United States.

"Most of the good writers are in internal exile, in external exile, or in prison," Jack Macrae said in an interview. Macrae is chairman of the International Freedom to Publish Commmittee, and a representative of the Association of American Publishers.

The publication of Soviet writers in the United States is not likely to increase soon, Macrae said. According to Soviet officials, the United States and the Soviets last year signed 333 book contracts, compared to 671 in 1979.

"The situation for writers has not improved," Macrae said. He said about 40 Soviet writers are in prison or in exile here "but now there is a new leadership, and we are here in part to demonstrate our hope that the situation will improve."

The American books here this year "were selected to show Soviets what has been going on in the U.S. in the last few years," Macrae said, including developments in the women's movement and criticism of the U.S. involvement in Vietnam.

Macrae and other members of the selection committee, which was headed by writer Kurt Vonnegut, have come under fire from the National Endowment for Democracy, which argued that the books chosen failed to reflect the shift to the right that has taken place in the United States, according to some of the publishers here.