Good consumer rule of thumb for celeb bios: The longer the subtitle, the lamer the book. Sid Caesar was one of TV's greatest sketch-comedy clowns, fearlessly physical, with manic intensity for getting the Big Laugh. But his autobiography is puny and tin-eared, full of puffery utterly uncharacteristic of the man, such as, ''Imogene [Coca, his costar] and I became television's royal couple in the early 1950s.'' The stuff about his famous ''Writers' Room,'' in which Woody Allen, Mel Brooks, and Neil Simon, among others, competed to place their jokes, has been heard a hundred times. Padding the book with transcriptions of his famous skits, Caesar doesn't render unto Caesar his due.