KPFK (90.7 FM) is devoting all day today to a Pacifica-wide marathon airing of audio tapes from the network's half-century of radio archives. It starts at 4 a.m. with an hour of W.E.B. DuBois speaking on tape, followed by an hour of Malcolm X and an hour of women from the civil rights movement such as Rosa Parks and Lena Horne. Others to be heard through the day include Martin Luther King Jr., John Coltrane, Duke Ellington, Paul Robeson, Studs Terkel, Woody Guthrie and the voice of Patty Hearst on a communique from the Symbionese Liberation Army. The complete schedule is here. It's to raise money for preserving the archive.