RAP GOES MAINSTREAM AT UNIVERSAL AMPHITHEATRE

You know rap music--the once raw and radical sound that was born on New York ghetto streets--has become mainstream when six rap acts play the Universal Amphitheatre as part of a national tour sponsored by a soft-drink company.

Because the bill didn’t include the harsh, political emphasis of an Run-D.M.C. or the hip, inventive flair of an L.L. Cool J, the evening seemed even tamer than it might have with weightier fare. That, however, didn’t stop the predominantly teen-age, middle-class audience from enjoying the show.

UTFO, whose hit about an arrogant girl, “Roxanne, Roxanne,” spawned a chain of “answer” records last year, got the crowd on its feet with an energetic, dance-oriented set. The L.A. Dream Team, one of the few successful rap groups to emerge from this city, followed with its lively, boisterous delivery. The group’s lack of variety and substance didn’t dampen the enthusiasm of the audience, which chanted along with profanity-laced gusto.

Full Force, the Brooklyn-based sextet that wrote and produced “Roxanne,” had an authoritative R&B;/rock approach that made the group appear to be the one act on the bill that could expand its following beyond the rap audience. The group’s act has improved tremendously over the weak showing it made at other local venues earlier this year.

The Fat Boys, the evening’s headliners, have comical value but remain musically monotonous. It’s going to take a fresher focus--and stronger material--to elevate the group beyond its novelty status.