FICTION : THE PIRANHAS <i> by Harold Robbins (Simon & Schuster: $21.95; 318 pp.).</i>

Our protagonist in this lightning-paced, vintage-Robbins story is Jed Stevens (nedi Stefano), who has a major problem: disassociating himself from his Mafia family, as his own father did years before. It’s easier said than done despite the apparent support from Uncle Rocco, who now heads the family. Jed quickly finds himself surrounded by piranhas--both literally and figuratively--as the family business embroils him in the international drug trade. All the Robbins imprints are here: sexual high jinks, amoral characters wheeling and dealing in the world of junk bonds and other fleece-the-public strategies. Jed, trying desperately to hang onto the legitimate business he inherited from his father, finds his own life the wild card in this winner-take-all battle among the flesh-eaters of Wall Street and Hollywood.