''Strange Fruit,'' a 57-minute documentary written and directed by Joel Katz, relates the intricate and intriguing history of the title song, a pioneering attempt to inject social protest into popular music.

First performed by Billie Holiday in 1939 at Cafe Society, the Greenwich Village nightclub, the song, a slow lament, is a metaphorical evocation of the racist lynchings that once plagued the American South. The ''strange fruit hanging from the poplar trees'' described by the lyrics is the body of a black man.

Holiday recorded the song soon after, and it became part of her standard repertory. (The documentary contains a striking clip of her performing it on British television near the end of her life.) Over the years ''Strange Fruit'' has been recorded dozens if not hundreds of times, by performers from Abbey Lincoln (who appears in Mr. Katz's film) to Sting. Its origins forgotten, the song was absorbed into the African-American cultural tradition.

But as Mr. Katz reveals, saving his bombshell for the film's midway point, ''Strange Fruit'' was actually the work of Abel Meeropol, a Jewish social activist who at the time was teaching at the DeWitt Clinton High School in the Bronx. Meeropol, who used the pen name Lewis Allan, was part of the radical socialist movement that attracted many New York Jews in the 1930's: ''Strange Fruit'' was written not from experience but from empathy.

Mr. Katz's polished, well-structured film uses carefully chosen newsreel scenes (including some compelling clips of Union Square in the 1930's) and interviews with a range of commentators (Amiri Baraka, Pete Seeger) and witnesses. Among the latter are Meeropol's sons, Michael and Robert, whom he and his wife adopted after the boys' parents, Julius and Ethel Rosenberg, were executed for spying in 1953.

STRANGE FRUIT

Produced, directed, written and edited by Joel Katz; directors of photography, John Miglietta and Thomas Torres; score by Don Byron, and song ''Strange Fruit'' by Lewis Allan (Abel Meeropol); Dorothy Thigpen, narrator; released by California Newsreel. Running time: 57 minutes. This film is not rated.

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