DOROTHY L. SAYERS, a bellicose mountain of a woman, dressed in mannish tweeds, a pince-nez glittering on her snub nose, torrents of crushing scorn for imagined enemies trembling on her lips, is not easy to love; but like her detective, Lord Peter Wimsey, whom the actor Ian Carmichael clothed in a diffident charm, she has been lucky in her interpreters. She forbade a biography until 50 years after her death in 1957, but in vain. Janet Hitchman's recent study was notable for retrieving from the public record the darkest of Dorothy's many secrets, but was sketchy for want of sources. James Brabazon was a friend of the writer, and his perceptive new biography is official, approved by the dark secret himself, Dorothy's unacknowledged illegitimate son. It is an even-handed, fully documented account that can hardly be accused of whitewashing its subject.

Nothing made her crosser than curiosity about her early life. "I thoroughly dislike all retrospect," she declared, yet the most interesting documents Brabazon found among her papers were two unpublished accounts of her childhood, one autobiographical, the other lightly disguised as fiction. They take her from her birth to an aging Oxford couple in 1893 up to 1911, when her unhappy schooldays ended. She grew up surrounded by servants, governesses and aunts, and knew nothing of other children until she was sent to school at 15. The little girl was remembered by the grown woman with unsparing revulsion as a self-dramatizing fantasist, a conceited, deceitful prig whose emotional responses were to books, not life: real life situations left her feeling cold and hypocritical.

Dorothy was quick and clever. She could read at 4, knew Latin and French by 6, and if she had a smug certainty of her own superiority, no doting adult discouraged it. But at school, where she showed off her superior learning and was clumsy at games, she discovered she was a misfit, heartily disliked by girls and teachers alike. Her defense was playing the buffoon, her solace writing up storms of thrilling verbiage. She would get even by being famous: "One day I will show them. I will set my feet on their heads."

She was thought insincere, and no wonder; for she had no idea of her real self: "I never can write about my feelings," she told her parents. But she could invent feelings and characters, while burying her own unruly sufferings deep and paving over the hiding place with orderly rationalizations. And if she could not be loved, she could at least attract attention. A bad case of measles added a gratuitous increment to her misfortunes: Her hair fell out and she had to finish school in a grotesque wig.

At Somerville College, Oxford, in 1913, she found a few kindred spirits for the first time, girls who could quote Cyrano and write sonnets, though even they found Dorothy overly earnest, too loud in argument, in her sense of humor too coarse. Her enthusiasms were undiscriminating; she lacked a sense of how far one can go without losing one's audience. Her professors deemed her "somewhat lacking in self-restraint," showy, not solid, her style spoilt by slang and rhetoric.

She played up spectacular crushes on men, and boasted that love-making was a game. It wasn't all fun when she fell in love with a poetic war invalid to whom she was only a confidante in his affairs with more attractive girls. Later she fell for an ostentatious Americanized Russian Jew living the literary life in London. Her tormented letters to him after the "affair" fizzled out show her with her defenses down. She cried every night for three years.

Luckily she had creative resources that were to make up to her in large measure for her inability to establish happy intimacies. One day in 1920 during a disconsolate visit home, Lord Peter Wimsey "walked in" to her imagination. Within months she wrote her first detective novel and found her first real job--working as a copy-writer for an advertising agency. It suited her to a T.

She never fell in love again, though she started an affair with a rather cheerful automobile mechanic. It was no romance, but it did mean actual bed, not just talk. When she got pregnant, she was already so ample nobody noticed. The baby was delivered during a brief leave and a faithful spinster cousin recruited to look after him. Dorothy paid the bills and occasional visits. Her son was never sure who his mother was until she was dead.

Now she lacked only a husband, and settled for what she could get: something of a journalist, boozer, and gourmet. She called him Mac and from the beginning she was the breadwinner. As a mate, Mac was a lot less than she reckoned life owed her. No wonder she lavished on Lord Peter Wimsey every imagined virtue her real men had wanted, including charm. At least she meant Wimsey to be charming. It was part of her failure to sense limits that he should make on many a reader much the same impression poor Dorothy made on her schoolfellows.

Wimsey is as preposterous as James Bond, but Harriet Vane, the woman he marries, is closely modeled on Dorothy's own image of herself. Gaudy Night, a late novel featuring Harriet Vane and set in Oxford, is as close as she ever got to writing a serious novel, dealing not with human relations but intellectual integrity. The novel's pretentious longueurs masked that Dorothy was on to an important truth, better enunciated later in a fine essay called "The Mind of the Maker": that the deepest human fulfillment is in creative work. Her writing, which she claimed to do mostly for money, was literally her salvation.

When literary success had sufficiently enriched her, she resigned from the ad agency where she had long been a stunning presence "thundering down the famous spiral staircase . . . her beloved cloak floating behind her," and turned her back on Wimsey as well to commit the remainder of her life to what she thought important.

She had always had an uneasy relationship with the Christian church, bitterly resenting her confirmation. And yet the institution described by Chesterton as a chariot "thundering through the ages . . . the wild truth reeling but erect" could hardly fail to appeal to her. And so when she was asked to write a play for the 1937 Canterbury Festival she fell to eagerly, vigorously reiterating the theme of Gaudy Night--that "what we make is more important than what we are." She turned to radio, to write a series of plays about the life of Christ, using her own jazzed-up version of the New Testament. The American slang offended many, and her talk of "the judicial murder of God" started a row. But the church knew a good propagandist when it saw one, and she was offered a doctorate of divinity in 1943, the first woman ever. In spite of her passion for costume, ritual, and honors, she refused it. She had often made it plain that if Christianity was something she apprehended largely with reason, not feeling, there was one element she knew with anguished intimacy, the sense of sin. Her own "sin," Brabazon suggests, was the stumbling block.

In her last years she found a calling she thought worthy of her, the fruit of a friendship with the Anglican writer, Charles Williams. He put her on to Dante, and though she then knew no Italian, she recognized a soul mate: "What a writer! God's body and bones!" Her last 13 years wer spent translating The Divine Comedy. Alas, her Inferno struck C. S. Lewis as being more Browning than Dante.

After Mac's death, pigs, cats and cactuses were her companions. Warier company she found at the Detection Club, a society of crime writers she had helped found. She was largely responsible for its mumbo-jumbo ceremonies which, during her tenure as president, produced more embarrassment than fun. When she dropped dead at 64, while her cats waited for their supper, only a few regretted a woman who had consistently retreated from emotional involvement into intellectual pattern-making. One was James Brabazon, whose sensitive, responsible and indeed affectionate biography she would have hated.

Still, she would have been relieved that he did not avail himself of psychoanalytic insights. But wrongly; for they might have shown her strange and often repellent nature for what it was--not willful but tragically inevitable. Anthony Storr's The Dynamics of Creation describes how people deprived of the sense of basic trust in early life can sometimes use their creative abilities as a defense against profound states of misery and alienation. Everything Brabazon tells us about Dorothy Sayers, down to seemingly insignificant details of dress and behavior, suggests that she was a schizoid character, one of those somehow deprived in the early relationship with the mother. Such people, finding personal relationships both meaningless and threatening, search out meaning in ideas. In the controlled world they bring into being when they happen to be writers, they can set things to right, making up for what life withholds and perhaps even enjoying fame. Dorothy was absolutely right in setting creativity as high as she did. Her search for meaning took her from Wimsey to Dante, the ridiculous to the sublime; yet the spontaneous detective novels express more of the genuine, hidden Dorothy than do her translations of the world's great literature, where the meaning is borrowed. It's the novels that survive.