ON THE TOWN: We've heard of unlikely pop stars. But how about Roger Hedgecock, the former mayor of San Diego who was convicted in 1985 on conspiracy and perjury charges stemming from illegal contributions to his 1983 mayoral campaign? The ex-city boss has formed a band, the Arnold/Hedgecock Experience, which opened for the Tubes at the Belly Up Tavern last weekend. The group performed such frat-rock classics as "Wild Thing," "Money" and "Louie Louie" and is expected to record a single for an independent label later this spring. . . . And whoops--who says hailing from L.A. isn't considered a black mark against your name? Local faves, Concrete Blond, who've been on a nationwide tour, opening for Dave Edmunds, got the ax from Washington Post reviewer, Geoffrey Himes, who complained: "Concrete Blond is the kind of band that would never get a major label contract if it weren't based in Los Angeles. Washington, for example, has a dozen unsigned bands far more original and far more appealing than this trio . . . (whose) songs were even more turgid and self-indulgent than they are on record."