A novel about a 34-year-old mongolian idiot sounds like a recent translation from the French or a sick joke, but this one is no joke, though it's extremely funny, touching and exhilarating. The author is a professor of psychiatry, and this is her first novel. The precision of her observation and her knowledge of what it is to be profundly retarded are not surprising, but her ability to make shapely art of it is.

Sanjo - not an acronym or a household product - is Sandra Joanne, the hefty, wedge-shaped daughter of Morris and Flo Bernatsky, born in her mother's late thirties. In spite of the in-laws' talk of a "home" and her husband's panic, nothing persuades Ma to give up her only child. For Morris the birth of his daughter is a single step from youth to old age: he spends the next three decades collecting pills in case he should decide to commit suicide - "a precautionary hobby."

Flo's commitment to motherhood is wholehearted, without self-pity, and unlike other mothers in the animal kingdom, she is "contracted in perpetuity." At 70 she watches "Sesame Street" with Sanjo just as she had long ago watched "Howdy Doody," a witness to the evolution of children's television.In the same manner generation of children have said, "Say you're a dope, Sanjo," and been goodnaturedly obliged, or called her "Chinko" because of the epicanthic fold that hoods her eyes - though there are many other peculiarities in her design dictated by the one extra chromosome responsible for Down's syndrome: a flattened nose, teeth like pegs, a heavy, unsteady gait with feet spread wide, arms dangling with palms facing backwards.

Her world is small, inside and out. She can't code what she sees without calling touch and taste into play; concepts like numbers and days of the week are beyond her; she is continent except when excited or depressed; she can comb her hair, take a bath, and with great effort put on a wraparound skirt. She loves to cut out cat pictures from magazines with blunt scissors; books read to her, although she doesn't understand what she hears; to watch children jumping rope, though she could no more jump than fly.

She had learned by experience as horrifying to Ma as it is ludicrous to read about that masturbation ("nice-nice") is not done in public. Her parents have decided against her wearing makeup lest she be seen - by whom? - as attractive, yet she is not without sexual experience. The good-natured mailman helps her into his truck now and then to let her happily stamp envelopes "address unknown" or "special delivery" while he takes his pleasure and afterward rewards her with a Hershey bar. "Mr. Niemeyer was very good to Sanjo. He never hurt her, talked nice to her, always made sure she was properly dressed when she left the truck, gave her candy, and sometimes...a letter." (Her brain makes some connections. When Poppy takes her to a porn movie, misled by its title into thinking it a kiddie flick about pussycats, and falls asleep during the action, he can hardly appreciate Sanjo's meaning when she comments afterward, "Special "livery.")

Ma and Poppy are her world, but it's impinged on by relatives and neighbors: a nice 14-year-old drug addict who reads "Bugs Bunny" to her; a 4-year-old new neighbor who readily accepts her as a playmate, then growing wiser as she makes friends her own age, turns on her. This Sanjo grasps, for she is alert to feelings: when her parents raise their voices she recognizes "bad talk" and cries if it won't stop. When the 4-year-old joins other little children who taunt and torment her, Sanjo is bewildered. "She had no template against which to measure treachery. She looked about in sorrowful confusion, her eyes widened in the same frightened puzzled look seen in any helpless creature at bay." Yet she has known little unkindness, and even has her moments of bliss, smiling, with head thrown back. Bliss can be occasioned by the smell of brand-new shoes or touching a silky rabbit.

Her safe, steady world is after all no more permanent than the vigilant Ma who programs it, and inevitably 70 years and high blood pressure culminate in a stroke. Sanjo visits her mother, stangely garnished now not with face packs and curlers but oxygen mask, funnels and tubes. She responds to the crooked twist of her face with the laugh she supposes it's inviting. Ma's failure to respond frightens her. "Get up, Ma. Come on," she says after Ma has lain mute for days, and begins to rip out the tubes. "What's the matter with you?" asks Poppy, dragging her away, having for a moment forgotten the answer to his question.

With Ma gone Sanjo become "the problem," whimpering her sense of loss and regressing to helplessness. She lies in bed, saying to the dark, "Hurts me," while Poppy goads himself to consume his pill collection. "O.K., Morris, it's now or never." Instead he is persuaded to get rid of Sanjo. "Believe me," says his brother, "it's the only way." The institution chosen is admirable, its director and staff sensitive, caring people, but of course too busy. With 108 retarded people to keep track of, the new world has to be regimented. But there are new things to learn: taking showers, eating eggs, feeling and smelling animals at the petting zoo - Sanjo appositely names the sheep "sweaterboy." She graduates from the most retarded group to one more independent where she is painstakingly taught to make perfect bows for gift wrappings. Life is not half bad - she gets hugged was well as yelled at. She learns more than anyone ever tried to teach her before, even how to count to two. Happy ending enough. Yet anoth er happy ending is in store. Poppy, Consumed with guilt, takes her h ome. The rejoicing neighbors declare him a saint. No mention of the fact that he's 72 and the homecoming can't last. Still, its an occasion of great joy for now.

A glimpse into the life of a person with an IQ of 30 ought to be arid and claustrophobic, but because of the author's verbal high spirits (the metaphor making, while brilliant and hilarious, gets compulsive at times), the clinical precision of her descriptions (the onset of a cardiovascular accident, birds deciding to fly south, a boy overdosing, a spider casting it's web, a baby's progress from blastocyst to diapered cherub, a conscientious young mother playing chicken with her VW bug on the superhighway), her sense of humor, insight, and lack of sentimentality, the story of Sanjo is liberating. There is a rich feeling of multiplicity, a reconciling sense 4-year-old girl, a sensitive psychiatrist, a confused expressions of the same miraculous abundance.