Jack Twiller, the hero in William Kotzwinkle's ninth novel, knew how to handle girls. In wading pools, he nonchallantly pulled off their tops. When his friends played post office at his birthday party, Lily Induris invited him to mail a letter. Never mind that Lily had cake crumbs in her curly hair and a Band-Aid on each knee. She did not pull away after their lips touched.

But then Jack begins to mature, and his life becomes a never-ending quest to discover what comes next. His secret source of strength is a comic book fantasy world. He is the Masked Man and Secret Agent X-9, Don Quixote in the small-town America of the 1940s and 1950s, "serving the cause of freedom and justice" and searching for a truly "Unforgettable Moment."

An underground hero long before mass-market publishers discovered him, Kotzwinkle has hitherto specialized in fairy tales, illusions, sorerers and post-death adventures. He is best known for "Fata Morgana" (1977), featuring a combination Christopher Robin, James Bond and Inspector Clouseau, and the "The Fan Man" (1974), a stream-of-consciousness wandering amid drug-induced weirdness (nearly 10 pages of the word "dorky" printed over and over again).

Kotzwinkle is a master of fantasy, of worlds that slide through what he terms "crack in reality's glass." Like Tom Robbins, Tom McGuane and other young writers, he subscribes to the controlled craziness school of literary thought. Its tenets are that the world is unavoidably irrational, that the only escape is partial insanity and that novels therefore need no logical construction or story development. Characters drift along, passing through unreal and real experiences with equal aplomb. In his latest book, Kotzwinkle quotes Mark Twain's warning that "persons attempting to find a plot will be shot."

But Jack Twiller's painful pubescence does force Kotzqinkle to adopt a story line: the hero's growth from back yard cowboy games to his awareness that after high school he might have to "march out of the last assmebly with his diploma in hand and go straight to the Carvel stand to get to job peeling bananas."

Kotzwinkle also demonstrates an excellent ear for the rhythms of childhood, a time when parents are forever warning that BB guns shoot out eyes. Even the best intentions can provoke a mother's distraught, "How could you do this? I carried you inside me," and a father's devasting, "Your mother's heart is broken."

Although Jack Twiller's childhood dies, his fantasies and his search for female perfection remain. In place of comics, he emulates James Dean. Old enough to own a car, he drives to Lily's house and pushes the doorbell, confident that "Dean was with him tonight, directing the scene."

"Did you want to see me about something, Jack?" she asks.

"Yeah . . . ah . . . yes, yes, I did, " he mumbles, trying to remember what Dean did next in "East of Eden."

That particular mission ended in disaster, but at the climactic senior prom, Jack knows Dean has helped him master "mature, intelligent casual conversation."

"Lotta different types of corsages here tonight," he tells his date.

Later that evening, as they drive away from the prom, he checks "his mouth out in the sideview mirror to see [that] he had his lips shaped right. mPerfectly natural."

Twiller circles, "approaching the make-out lane from behind, so he'd be facing downhill into the valley, an inspiring sight for the night of nights."

Dean himself couldn't have done better.

The conversation continues. "It was quite a dance, huh?" Jack asks.

"Really swell," says his date.

After more witty repartee, Jack realizes that he must make his "Big Move," that he must "steel himself for a maneuver."

Kotzwinkle offers no illusions or fantasies about what happens next. "Jack in the Box" ends as it should, with Jack Twiller entering a world of new vulerabilities and possibilities. Comic books and James Dean have failed him, the fantasy girls have faded and the boy-man is left alone in the front seat of his father's car, facing a living, breathing human being.