Counterculture hero Jerry Garcia of the Grateful Dead is going commercial. He's part of the new $20-million radio advertising campaign for Levi's 501 jeans, along with Leon Redbone and bluesman Robert Cray. The rotund, grey-bearded Garcia ends his spot by singing, "501 blues, shrink to fit only me." An advertising agency approached the Dead about doing a commercial as a group but that was rejected. Garcia, however, took the idea to a bluegrass group he sometimes sits in with and the commercial was taped. Garcia's fee was not disclosed.