Garson Kanin, screenwriter, playwright, director, sometime novelist and inveterate namedropper, runs true to form here. Though his subject is ostensibly the "lusty, exciting, lovable, but maddeningly elusive" John J. Tumulty, a gifted actor whose imaginary life and loves are carried on in San Francisco around the turn of the century. Kanin has gone out of his way to drag Spencer Tracy, Katherine Hepburn, Arthur Rubinstein, Thornton Wilder, Marlon Brando and other cronies into this feeble piece of fiction.

One Hell of an Actor is a novel written in journal form, the individual entries detailing one episode or another in Kanin's supposed 37-year search for the "real" Tumulty. The hunt turns into a sort of literary mystery, with Kanin himself cast as the would-be detective; conservations with those who were acquainted with Tumulty and research in three countries gives the sleuth grand opportunities to spout theater and Hollywood lore, but eventually he concludes that his deceased quarryhs "complexity and contradiction" will always foil him.

Along the way, we meet such types as The Old Actor (who once worked with Tumulty), Big Director (Tumulty's adopted son), and JJT IV (his cocky, illegitimate great-grandson). Given Kanin's proclivity for facile philosophizing and clumsily artificial dialogue, neither they nor any of the other characters, real or imaginary, have much to say that's worth remembering. John J. Tumulty may have been one hell of an actor, but all Kanin has made of him is one hell of a turkey. (Harper & Row, $8.95)