In the world of rock, few artists can claim even one enduring ensemble to provide for their pension. Gruff-voiced singer Paul Rodgers can bank on three. His current liaison with Queen seems an unlikely pairing, but it's a reliable paycheck nonetheless. His first band of note, Free, was a formidable blues-based outfit with a late-Sixties pedigree and a classic-rock staple in "All Right Now." However, success wasn't assured until Rodgers and drummer Simon Kirke enlisted Mott the Hoople guitarist Mick Ralphs and former King Crimson bassist, the late Boz Burrell, and morphed into Bad Company. The first signing to Led Zeppelin's fledgling Swan Song record label, the group released a 1973 debut that paved the way for continuing hits — "Can't Get Enough of Your Love," "Bad Company," "Feel Like Making Love," and "Rock 'n' Roll Fantasy" among them. A second attempt, with singer Brian Howe replacing Rodgers in the mid-Eighties, became a dubious proposition; despite some chart equity, the new generic sound wasn't worthy of the band's earlier acclaim. A 1998 reunion of the original lineup was short-lived, and indeed Friday's regrouping at the Hard Rock appears a one-time affair. Nevertheless, the band will attract a good company of enthusiastic fans.