A rap concert at the Hollywood Palladium was marred Saturday night by a free-for-all involving more than two dozen rival street gang members, authorities said Sunday. The show, which was halted momentarily until security guards stopped the fighting, featured rap groups UTFO, Salt 'N' Pepa, Eazy E, N.W.A., Heavy D and the Boyz. The violence erupted shortly before 10 p.m., involving gang members wearing "colors" that identified their affiliations, Los Angeles Police Sgt. Mike Schneider said. Street gang members were blamed for a riot that erupted at a Run-D.M.C. concert at the Long Beach Arena in mid-1986. About 40 people were injured in that incident. The promoter of the concert canceled a subsequent show scheduled at the Palladium.