Jack Lemmon, star of "Missing," insists that the virulently anti-American movie says things "I happen to agree with," but that he would have taken the part even if he disagreed with the movie's message. It's "like playing Richard II."

Not quite.

Charles Horman, 30, an American left-wing journalist living in Chile during the 1973 overthrow of Salvador Allende, disappeared and was killed. "Missing" charges that the U.S. government assisted the coup and the murder of Horman, who "knew too much." The movie does not suggest why Horman's friend, who knew all that he knew, was unharmed. But, then, the movie, a tissue of tendentiousness, alleges, on the basis of wild inferences, that Horman and others "knew" many things that, in fact, are untrue.

The movie begins portentously, and fraudulently: "This film is based on a true story. The incidents and facts are documented." "Based on" is a weasel phrase. Journalists and lawyers eager to find evidence of U.S. complicity in the coup have ransacked the documents without finding evidence. A Senate committee that would not have been sad to find evidence said it found "no evidence." Horman's father's suit charging U.S. complicity in the death of his son was dismissed for lack of evidence. To paranoiacs that is especially sinister: the utter absence of evidence, as testified to by Secretary of State Edmund Muskie, proves how comprehensive and diabolical the conspiracy was--and is.

Challenged about the movie's truthfulness, Costa-Gavras, the Greek director, says he did not try to prove the truthfulness "of anything and practiced poetic license," but is "convinced" that America "had something to do" with Allende's overthrow. By way of alibi he says, "Don't ask a film director to be a political technician"--whatever that means. Don't ask him to be truthful when he is busy tutoring America in ethics.

His movie is one of the hit-and-run acts of cowardice called "'docu-dramas," a label that is a license to lie and smear, using references to real people and events to give a patina of authenticity to innuendoes and fabrications. Universal's president announces himself proud of this "totally true story," which is showing in 600 theaters, grossing millions. The wages of anti- Americanism are handsome.

William Wolf, movie critic of New York magazine, welcomes this "tough, outspoken" movie as evidence that Hollywood is "developing a taste for controversy." Tough, outspoken Joe McCarthy should have made movies: he, too, had a taste for controversy. Vincent Canby of The New York Times says that in spite of its "unsubstantiated conclusions" the movie is "healthily provocative." It was made by and for the sort of people who consider themselves virtuous because they are not Richard Nixon. He never lied as smoothly as this movie does, and he was not considered "healthily" provocative.

Stanley Kauffmann of The New Republic is not at home in the intellectuals' slum inhabited by persons who are tolerant of lies from the left. He says of Costa-Gavras:

"His picture is a mixture of caution and irresponsibility. He cautiously names nothing and no one precisely; he glibly implies deep guilt, making empty heroic gestures of protest without foundation and without risk. It's thus a perfect Hollywood liberal picture, playing to a gallery of trained seals and to another gallery of the gullible, for the happiest kind of Hollywood profit--big returns plus big ego-satisfactions. . . . "

Only once does the movie hint at what Allende did that provoked the military coup. One of Costa-Gavras' cloying young idealists says: "They (Allende's forces) were trying to do something new here." That "something" would not have struck Eastern Europeans as novel.

In 1970 Allende came to power with a 39,000- vote plurality out of nearly 3 million votes: 62.7 percent voted against him. With no mandate he began attacking what he disdainfully called "bourgeois" democracy--elections, pluralism and all that. Chile's congress refused to confirm him as president until he subscribed to a bill of rights. He did so, he assured a colleague, only as a "tactical necessity" en route to the "overthrow" of the "bourgeois state" and its replacement by "total, scientific, Marxist socialism." He harassed rival newspapers and parties, imported thousands of revolutionaries, imported arms through Cuba's embassy, and ran inflation up to 350 percent. After the coup, Eduardo Frei, a former president and one of Latin America's most distinguished democrats, said:

"The military have saved Chile. . . . A civil war was being well prepared by the Marxists. And that is what the world does not know, refuses to know."

This information and all other traces of truthfulness are missing in "Missing."