The Case of the Stuttering Saint : SPEED <i> By Mark Harris (Donald I. Fine: $19.95; 257 pp.) </i>

In “Speed,” Mark Harris, the author of the wonderful Henry Wiggens novels “Bang the Drum Slowly” and “The Southpaw,” has whipped up a confection of ironies--sweet, delicate, sometimes delicious, but ultimately insubstantial. Which is too bad. The title character deserves better.

Speed, of course, is the ultimate irony. Why he bears the name is never explained, but he’s called it by all, though only the narrator, his brother, truly understands how apt it is.

Speed is a saint. Speed is a wizard. Speed is a dreamer. Speed is a visionary. Speed is better looking than his brother but can’t get a girl. Speed fell on his head as a baby, or may have been pushed by his brother off a table. Hell, as a kid Speed invents the one-handed jump shot and revolutionizes high school basketball, which would be enough of an accomplishment for anyone, but Speed adds several more. He writes a novel. He plows the fields. He rebuilds the family apartment. He opens his heart compassionately to the sick, the lame and the halt. He detests prejudice and burns against deceit, shining like a moral beacon to guide the mere mortal around.

If only they could see. Then again, if they could, they’d probably just crucify him. Goodness like his doesn’t come often.

Speed’s cross-to-bear is that he stutters. Badly. So everyone thinks he’s slow. Only his brother, older by a year but millenia less wise and more calculating, listens to him, mainly because no one but his brother bothers to figure out what he’s trying to say.

To balance the fraternal equation, the brother naturally has a terrific gift of gab; he can talk his way into anything. “The world therefore believed I was superior to Speed,” the narrator tells us in the novel’s penultimate irony. “He was unable to express long or complicated ideas regardless of how expressive he may have been with his brilliant hands and his brilliant inventive creative mind . . . Father favored me, for father was of the world.” The Smothers Brothers--with depth and soul.

Somehow, through the sheer strength and beauty of Harris’ writing, most of the irony works, even if much of the narrative doesn’t. The story, a Bildungsroman, is told through the gauze of memory, as the narrator looks back from the present through the pre-World War II childhood and youth he shared with Speed in the New York suburb of Mount Vernon.

Their father, who may not be Speed’s father because his mother may have been having an affair with Babe Ruth, is the local police chief, a once-dashing fellow who’s never won the complete affection and devotion of their mother. Their mother comes from local wealth, having grown up in a Mount Vernon mansion called Walk a Mile House, dubbed for the fortune her advertising-genius father made by coining, among others, the famed Camel cigarette slogan.

Grandfather is a slick character, a schemer and a charlatan. He may be good with slogans but, blind as a bat, he can see neither the end of his nose nor anything that resembles truth, fairness or decency. He dismisses Speed as a dolt, and takes the narrator under his wing.

Much of what’s important in the story takes place in the grandfather’s domain. It is there our narrator has his first sexual experiences, under a set of electric trains, with a young black servant named Champrain, who mysteriously disappears that summer, never to be heard from or seen again. It is there he smokes his first cigar and drinks his first brandy. It is also there that he learns to commit fraud, which, of course, repulses his brother.

While all that is happening, Speed continues to earn his halo. He writes his brother’s school papers, and his brother becomes a genius in his teachers’ eyes. He applauds his brother’s interracial romance in this decidedly less tolerant era, as long as the romance is about love, not just sex. He continues to revolutionize basketball.

And then, like Champrain, Speed simply disappears when his brother talks his way into a job as a reporter on the Port Chester daily, a job Speed wanted desperately, but was rejected for because of his verbal handicap. The narrator tells us he’s spent the rest of his life in emotional disequilibrium, searching for answers, searching for his missing brother, ruing his own incapacity for having been nicer and more understanding to Speed when he was there.

Frankly, “Speed” would have been far more compelling had we just left the narrator stewing in Westchester and joined Speed on his uncharted odyssey. The life of the possible bastard son of Babe Ruth certainly would have been a trip to follow, even if he remained perfectly pure of heart.