With his bald dome, wraparound shades, and playful falsetto, this ace hook man should be familiar to hip-hop fans, thanks to videos like OutKast's ''The Way You Move.'' But the singer-producer's transition from background player to marquee star is rocky. Undercooked songwriting and overstretched choruses take away from Brown's Marvin Gaye-ish come-ons. While the Philly- soul-style ''Me, My Baby, My Cadillac'' is one of the year's best R&B singles, most of Mr. Brown suggests this crooner should stick to supporting roles.

