MOSCOW, SEPT. 8 -- The confiscation of 50 books written by Russian e'migre's and shipped here from the United States marred today's opening of the Moscow International Book Fair and raised new questions about the sincerity of Kremlin leader Mikhail Gorbachev's campaign for greater artistic and political openness, or glasnost.

Nevertheless, the fair did offer for consumption some early fruits of glasnost, including Soviet works spawned by the cultural thaw and others brought from abroad that give Soviet readers a more critical view of Kremlin policies or a rare look at the outside world.

The seventh biennial book fair here, billed as promoting "Books for Peace and Progress," brings together the largest collection in any communist nation of new literature from both socialist and western countries. Soviet citizens, by reputation among the world's most avid readers, turned out for the fair and poured through its exhibit stalls and books by the thousands all day long.

The 50 books seized by censors were the works of about 30 e'migre' authors and had been shipped to the fair by the Ardis publishing company of Ann Arbor, Mich., a firm that specializes in Russian works by authors not published in the Soviet Union. Ardis official Ellendae Proffer said that among the books were works by Soviet e'migre's Vitaly Aksyonov and Josef Brodsky, who now live in the United States, and Vladimir Voinovich, who lives in West Germany.

The books were seized because they were "insulting to the fair," Tankard Golenpolsky, an official at the Soviet publishers' clearinghouse Goskomizdat, said in an interview. He added, however, that they would be returned to Ardis at a later time and allowed to be put on display.

The book seizures, coupled with the heavy presence of Soviet plainclothes policemen, served as a vivid reminder of the strict controls this country keeps on access to the West and western paraphernalia.

Some American publishers also used the occasion to complain that 33 prominent Soviet writers are still being held in prison camps or psychiatric institutions. Said Association of American Publishers spokesman Alexander Hoffman: "We feel that writers ought not to be in jail, that writers should be published in their own country, that writers should be able to say what they want. That's not always the case here and sometimes that gets lost because of glasnost."

This year's fair, the first since Gorbachev launched efforts to promote a more open society here, has indeed offered a number of illustrations of that openness at work. For one thing, none of the dozens of other American publishers exhibiting here reported confiscations, and organizers of the popular display "America Through America's Eyes" said that for the first time since they began coming here in 1979, the books they shipped were not checked by censors.

And among the books displayed by Soviet publishers were several by Soviet novelists on themes that were taboo until recently. Among these were Chingiz Aitmatov's "Plakha," which deals with religion and drug use; Daniel Granin's "Zubor," a biography of a Soviet scientist imprisoned under Stalin; and Anatoly Rybakov's "Children of the Arbat," about the terrors of Stalinism.

This year, Soviet officials also granted visas to several American publishers who had been denied permission to come to the fair for the past six years, including Robert Bernstein, chairman of Random House, and Jeri Laber, vice president of the AAP. 3R fixes Both are leading members of Helsinki Watch, a human rights monitoring group.

But Soviet officials denied a visa to Catherine Fitzpatrick, the Helsinki Watch research director, who had been invited by the AAP to attend as a translator.

In contrast, the spirit of glasnost was awake and singing at a number of exhibits at the fair, which this year featured tens of thousands of books from more than 100 countries displayed in two pavilions at a Moscow fairground.

One display was devoted entirely to Moscow News, the official weekly that has played a leading role in the glasnost campaign. In the Israeli exhibit, meanwhile, Soviet Jews held an impromptu debate with David Drangonsky, a representative of the government-sponsored Anti-Zionist committee, which is highly critical of Israel.

At one American stall, Soviets were able to peruse American journalist Seymour Hersh's "The Target Is Destroyed," a critical analysis of the Soviet Union's shooting down of Korean Airlines Flight 007 in 1983, while at the "America Through America's Eyes" exhibit Soviets were offered a rare glimpse at both negative and positive aspects of contemporary American politics and culture. On view were such critical works as Joseph Trento's "Prescription for Disaster," an investigation of the 1986 Challenger disaster; and Anthony Lukas' "Common Ground," which focuses on racial unrest in America following the 1968 assassination of Martin Luther King Jr.

Also on display were such examples of lighthearted Americana as "The Random House Book of Mother Goose," the Sears mail-order catalogue and Dr. Seuss' "You're Only Old Once."

In all, the exhibit proved one of the most popular features of the fair, with Soviets waiting in line for hours to jostle past security agents and into the crowded stall