THE DIDDLEY BEAT is the most famous rhythm figure in rock 'n' roll history, but Bo Diddley himself may well be the most underrated of rock's early pioneers. Many casual rock fans think of the singer with the thick glasses and square guitar as a man with one great idea: that "bum-de-bum-de-bum . . . boom! boom!" beat. The new anthology album, "Bo Diddley: The Chess Box," proves however that Diddley revolutionized the use of rhythm in American popular music as thoroughly as James Brown did.

As Robert Palmer points out in his excellent essay in the box set's 24-page booklet, American music criticism (and U.S. copyright law) accepts the European bias that lyrics, melody and chords are the substance of a song and that rhythm is only secondary. Diddley (born Ellas McDaniel in McComb, Miss., in 1928, and raised from age 8 in Chicago) "re-Africanized" American music by making rhythm primary. He played chugging, jerk-and-pause rhythm guitar, which he set against rumbling tom-tom drum patterns, Jerome Green's maracas and the call-and-response vocals. From these simple ingredients, he spun off countless variations on the Diddley Beat. His new box set is a veritable encyclopedia of funk rhythms.

"Bo Diddley: The Chess Box" contains 45 songs on three records, two cassettes or two CDs; included are four unreleased alternate takes plus eight songs that have never been on a U.S. album before. Thirty-four of the cuts come from his classic 1955-60 period (including several years when he was living and recording here in Washington), though 11 more document his lesser-known 1961-68 years. Included are the songs like "Bo Diddley," "I'm a Man," "Who Do You Love," "Mona," "Road Runner" and "You Can't Judge a Book by Its Cover," which have been recorded by the Stones, Buddy Holly, the Yardbirds, the Who, the Doors and Bob Seger.

Not included are songs like "Not Fade Away," "Willie and the Hand Jive," "Magic Bus" and "She's the One," which are all built atop the Diddley Beat. Diddley may have been limited as a singer and melodicist, but he was a revolutionary of rhythm.

BO DIDDLEY -- "Bo Diddley: The Chess Box" (Chess/MCA). Appearing through Sunday at Anton's 1201 Club.