THE FILM DOCUMENTARY ABOUT FILM is a genre whose potential is usually untapped. Those of us who are cinephiles usually get the most satisfaction out of specific profiles of actors, directors or studios. But even these usually offer only a few attractions. The documentaries that aim too high, such as Jeanine Basinger's lengthy series on PBS last year that purported to cover the history of movies, are doomed to failure.

This year, however, a film has appeared that has surpassed all expectations. "The Celluloid Closet," directed by Rob Epstein and Jeffrey Friedman and based on the book by the late Vito Russo, is thorough, honest, coherent and artful. Tackling the tricky, complicated question of gay Hollywood, the creators of this film acquit themselves admirably. The movie, narrated unobtrusively by Lily Tomlin, is a comprehensive view of the presence of gay themes and characters in movies from the very beginning to the present. We witness the dramatic evolution from total stereotype and vague innuendo to movies wholly about gay life, including realistic love stories (and, naturally, more sex and violence). The movie moves chronologically, seamlessly integrating montages that locate common themes in the movies of a particular period. These montages, such as those that show gay characters being attacked or killed, those that show them embracing, and one particularly unpalatable one chronicling the casual use of the word "fag," are cleverly assembled and produce strong quantities of the desired emotion.

The film elucidates the difference in movies' portrayal of male and female homosexuality (each of which alone would be enough for a documentary), pointing out that, as with cross-dressing, the female version is titillating to a mass audience and the male is laughable or repulsive. The film also deals with the boundary between male tenderness or "weakness" and homosexuality.

We also get a sense of the multiple agents responsible for creating a movie, the ways in which even the subtlest contributions of directors, writers and actors shape the final product. The directors, writers and actors who speak here feel responsible in varying degrees for the implications of their films. Farley Granger describes the actors' awareness of the homosexual themes in "Rope," while Shirley Maclaine wonders at the production of "The Children's Hour," a film wholly concerned with lesbianism, during which the words and ideas of homosexuality were never even mentioned on the set.

Other talking heads include gay personalities who are not identified with Hollywood, like Quentin Crisp and Susie Bright, contemporary straight actors like Tom Hanks and Susan Sarandon, and many overlapping figures, such as historian Richard Dyer, author Gore Vidal, and screenwriter Paul Rudnick. The heterosexual actors, for the most part, don't come off as well. Whoopi Goldberg and Sarandon radiate satisfaction with their own openmindedness, Hanks seems fairly happy-go-lucky both about his youthful homophobia and his recent embrace of a more sensitive persona. Harry Hamlin seems more perceptive than most, admitting his own tendency to question the sexuality of an actor playing a gay role.

In fact, the film's approach is analogous to reader-response criticism. The movies are studied not so much for their background or technique as for their impact, specifically on homosexual audiences. Those interviewed relate their own experiences, a method much more effective than hearing the speculations of an impersonal narrator. They describe having to forage for gay subtexts and innuendoes in old movies. Even within the range of this subject, we are presented with a wide variety of opinion: Arthur Laurents expresses a deeply felt, almost tearful anger at the movies' stereotypically effeminate caricatures of gay men, while Harvey Fierstein professes his fondness for and identification with these stereotypes. Susie Bright recalls with strong emotion the lesbian scenes and images in films that have moved her. Ron Nyswaner, the writer of "Philadelphia," recalls being gay-bashed in reponse to the horribly violent "Cruising." The power of the movies is clear. As Lily Tomlin says Hollywood has taught "straight people what to think about gay people and gay people what to think about themselves.

Another remarkable quality of the film is its creation of new emblems for homosexuality in cinema. The song "Secret Love" sung by Doris Day in "Calamity Jane," becomes an anthem of the revelation of a forbidden feeling, with its triumphant conclusion: "At last my heart's an open door, and my secret love's no secret any more." Apparently, k.d. lang, who provides a new recording of the song over the final credits, agrees with its relevance. The image of two men slowly dancing together, from an early experimental film by Thomas Edison, seems strange and haunting at the beginning of "The Celluloid Closet" but even more so at the end, where it is used to great effect, bookending the progress shown in the film, in which such images began as innocuous and then became an object of prurient curiosity and hatred, finally, as the directors hint, a symbol of possibility and hope.