WASHINGTON and Moscow may be talking peace, but it's war when it comes to Soviet-American film relations.Jack Valenti, president of the Motion Picture Association of America, angrily terms Soviet behavior "state-condoned piracy." The major Hollywood studios have imposed a boycott on movie sales to the Soviet Union. It won't be lifted, Mr. Valenti vows, until the Soviets live up to the terms of the Bern Copyright Convention (which they have not signed), and outlaw video piracy. The practice of illegally copying feature movies onto video cassettes, which are then sold or shown, is a worldwide phenomenon that costs the movie companies billions in lost income. But rarely is it carried on as blatantly as in the Soviet Union where operators, including organizations run by the state, appear to have no qualms about distributing and exhibiting pirated films. "Gone With the Wind" and "Rain Man" are just two of the many American movies that have been screened illegally on TV sets in the lobbies of Soviet movie houses and at growing TV salons all over the country. Even Soviet television has aired pirated United States pictures. During the past few years, however, the Soviets have begun to purchase some Hollywood products legally, and illegal video cassettes are competing with these movies in the theaters. "Gone With the Wind" appeared on regional television a few days after its Soviet theater premiere. According to Variety, the trade publication, MGM executives visiting Moscow were horrified to find their classic playing for paying audiences in a video parlor near the Kremlin a month before its Moscow opening. Even the fairly new "Diehard 2" has been announced as a forthcoming Soviet TV attraction, though the film has not been licensed for Soviet release. Two bootlegged Arnold Schwarzenegger movies were a lso aired on TV. The Soviet Union has five national TV channels and 123 regional ones. It also has some 200 cable networks covering most of the country, which aren't regulated by any laws whatever. Cable has offered pirated versions of one of the Rambo movies and "Moonstruck" among others. A Moscow-datelined story in The Hollywood Reporter said that American films were often recorded straight from telecasts originating in Finland or Turkey. Once copies are made, they are then dubbed into the local language. Showings in video parlors are openly advertised and admission costs more than the theaters. Soviet authorities say that only clips from movies are televised, but the stations show the entire film apart from the opening and closing credits. Valenti wrote to Vladimir Petrovsky, the deputy foreign minister. Mr. Petrovsky said the government shared the US studios' concerns, but that the boycott was "unjustified" because it penalized the Soviet public without "punishing all those who are guilty of irregularity of film shows." Another Soviet official said the authorities were considering registering all imported films. If an organization cannot prove that it has the rights to a film, it won't be able to show it. While the Motion Picture Association embargo certainly threw a shadow over the recent Moscow Film Festival, it is by no means "leak-proof." A great many foreign sales agents and independent producers are represented by the American Film Marketing Association whose president, Jonas Rosenfield, said that his organization could not impose a boycott. "We have some 110 member companies, and I doubt that they would all agree to join in," Mr. Rosenfield said. The Soviets have drafted laws, but Mr. Valenti called them "inadequate and feckless." A story in the Soviet paper Izvestia revealed that even the Ministry of Finance was involved in the bootleg operations which yield welcome tax revenues. Today's piracy is oddly reminiscent of the '50s and '60s when the Soviets, faced with a Hollywood refusal to sell them films, quite routinely hijacked prints of American movies in Europe and showed them in the Soviet Union. For the most part, these were pictures critical of social and economic conditions in the US. In a number of instances, the Soviets edited these pictures and in the case of "Mr. Smith Goes to Washington," they even added a propaganda postscript. Also pirated was a print of "Grapes of Wrath," which was supposed to convince the masses that poverty and misery reigned in the US. This backfired because Soviet audiences admired the number of cars shown in the supposedly poverty-stricken areas of the Oklahoma dust bowl. Eventually, the US State Department authorized selling movies to the Soviets, but limited sales to films which wouldn't lend themselves to anti-American propaganda. In recent years Soviet government organizations have sharply increased their purchase of Hollywood pictures, just as the number of Soviet-American coproductions has multiplied. Yet in the context of the overall foreign market for American films, the earnings from the Soviet Union are less than $1 million.