Jeff Beck stands alongside fellow ex-Yardbirds Jimmy Page and Eric Clapton as one of the greatest electric guitarists Britain has ever produced. His work in the past three decades has encompassed progressive, soul, jazz-rock, and instrumental music, winning him the accolade of ''the guitarist's guitarist'' from innumerable musicians' magazines. Yet despite his eclectic output and many collaborators, fans and critics alike hark back to the short-lived Jeff Beck Group of the late 1960s, featuring Rod Stewart on vocals and Ronnie Wood on bass, as his greatest single contribution to rock music. Some go as far as to say that ''Truth,'' their first album from 1968, was the first true heavy metal album, a prototype that set the style for countless (and inevitably less talented) outfits to follow.