Rap can be as nasty as it wants to be, and, thanks to the 2 Live Crew obscenity trial, everybody knows it. Yet explicit rap tunes everything from the exaggerated sexual boasts of the Crew to the ''gangsta'' playacting of N.W.A. pose a new and complex set of questions. Are sexual rap songs merely dumb-fun party records Redd Foxx set to a drum track or should they be treated as appalling antiwomen tracts? Are rappers who talk like thugs trying to dramatize conditions in the black community or merely toughening their image? Do they actually encourage violence? None of these new records fully answers those questions, but in its own way each addresses the contradictions inherent in explicit rap.
With the collection 2 Nasty 4 Radio, Warner Bros. seemingly wants to cash in on the raunch-rap controversy and hype its own rap roster. But except for Ice-T's goofy ''Girls L.G.B.N.A.F.'' (the first few initials stand for ''Let's Get Buck Naked'') and Roxanne Shante's squeaky-voiced strut, ''Brothers Ain't S---,'' the record merely confirms that Warners' rap lineup is hardly making hip-hop history. C