The mysterious Mr. Hitchcock; The Dark Side of Genius: The Life of Alfred Hitchcock, by Donald Spoto. Boston: Little, Brown & Co. 394 pp. $20.

Alfred Hitchcock's films thrive on contradictions. They mingle humor and horror, blur the appearances of guilt and innocence, make a strange equation of knowledge and danger.

Above all, they bring a rigorous artistic order to the most chaotic of materials.

In this immaculately composed biography, Donald Spoto traces such contradictions to roots deep in Hitchcock's inner life, arguing that his brilliant and disturbing movies were the product of a brilliant and disturbed personality. Using his own interviews with the director, talks with Hitchcock's collaborators, and - most imaginatively - clues embedded in the films themselves , he reveals ''Hitch'' as an unhappy giant, nursing secret wounds and sullen fantasies while outwardly playing entertainer to the world.

And so, more contradictions. On the surface, Hitchcock led a comfortable life. At school he was an ungainly but bright boy whose idea of a good time was studying railway timetables.

Breaking into the movie business as a title-card designer, he impressed everyone with his ability to master all phases of filmmaking, from lighting to coiffure. Decades of hits and misses - mostly hits - made him a world-famous multimillionaire, complete with a knighthood from the Queen and growing respect from cinema scholars.

Looking deeper, though, it seems Hitchcock was rarely content. He had a fear of intimacy, and fended off real friendship while cultivating odd fixations on certain women in his life, including Ingrid Bergman and Tippi Hedren. He worried about money even as his wealth grew enormous, and indulged at the table (sometimes disgustingly) while fretting about his health. His fastidious manner masked a preoccupation with bodily functions; his humor was often offensive or destructive.

And, as Spoto demonstrates, all these sad secrets made their way into Hitchcock's films, deepening and complicating them. Since he controlled every aspect of his movies, they can be read as seismic charts, marking a flow of energy and emotion that had little outlet besides creative work. Their themes and motifs - the mirrors in ''Psycho,'' the eye references in ''The Birds,'' the pairs and couples in ''Shadow of a Doubt,'' the constant killings and betrayals and reversals - stem not only from the storyteller's bag of tricks, but from his hidden store of obsessions, as well.

It's possible that Spoto paints too gloomy a picture, and that future studies will temper his verdict, though there may never be a Hitchcock biography that presents its case more tactfully or explores it more feelingly. Hitchcock might have derived more comfort from fatherhood than Spoto indicates, for example, while his rigid habits and continual traveling were surely a source of eccentric pleasure as well as a defense against inner disorder.

My own contact with Hitchcock found him a model of dignity and humor - he always put on a good show for the press - even though it came during what Spoto describes as a hard time in his life. And he continued to do valuable work almost until the end, turning out one of his most relaxed and friendly films (''Family Plot'') well into what Spoto considers his declining period.

Though this fine book comes close, perhaps no biography can capture the full complexity of such a consummate artist and troubled man, who caught the fancy of millions by staying true to his strangest visions - as a collaborator put it, ''beaming amid his nightmares.''