WILLIAM FAULKNER argued that the problems of children were not worth writing about. He wrote frequently about children himself, but he treated their lives as windows on the adult world, or as early parallels to mature venality, obsession, or tragedy. Similarly, he placed high value on The Catcher In The Rye mainly because the odyssey of Holden Caulfield was such an earnest and telling rebuke to contemporary morality.

Steven Millhauser's second novel. Portrait of a Romantic (his first novel was Edward Mullhouse 1972) is a rebuke to Faulkner's view of youth as trivial, for Millhauser successfully excavates childhood to reveal its hidden wonders and dismal dancers. His children are not paradigms of their own later existence, for they do not grow up, nor they mirrors of the grownup world, which exists in the novel only insofar as it illuminates childhood.

His children - three boys and two girls in continuing crisis from ages six to fourteen - are special creatures all in frenzied swarm around the incandescent dangers of the forbidden. If the children represent anything outside themselves it is as metaphor for conditions common to men, women and children of any age - mournful friendship, seductive decadence, the recurring tides of boredom, and an enduring flirtation with easeful death.

In his story, Millhauser presents himself as a kind of Proust of pubescense and adolescence. His book, written in immaculate prose, is a prodigious feat of memory, with an enormous density of fell and observed life. His narrator writes at one point of his desire to be an artist: ". . . if only I could create a world superior to this world, which would annihilate and replace it." This is part of the romantic strain in the narrator and the romantic strain in Millhauser as well, who achieves what his narrator yearns for. He creates a world that is exquisite in its tortures and terrors, a world which only the heightened consciousness of an artist or a dreamer could inhabit.

The children of this story would never be found in television commercials, family comedies, or on Little League teams. They live their lives in a solitude so inviolable that even companionship becomes only another agent for heightening isolation. They are constant readers with acute insights into literature and life. They grow bored with Stevenson, find meaning in Poe and Keats. They inhabit secluded hiding places in bushes beneath translucent leaves beside a secret stream, a private Eden in which faces and hands are colored with green-glowing innocence that should last forever, but will pass all too swiftly. They will move, then through other secret places - cellars, attics and passageways, into labyrinths of dust, history and precocious love, penetrating ever deeper into the dark and blissful horrors they all seek.

The story is narrated in first person by Arthur Grumm, whose opening paragraph echoes both Whitman and the Bellow of Augie March: "Mother of myself, myself I sing: lord of loners, duke of dreams, king of the clowns. Youth and death I sing, sunbeams and moonbeams, laws and breakers of laws. I, Arthur Grumm, lover and killer."

But Arthur leaves Whitman and Bellow swiftly behind and moves into a comic depiction of everybody's climactic moment in prehubescence - the show party. "One, two, three," says Arthur's cousin Marjorie, age six. Up goes her dress and down come her panties, nonplusing Arthur. He will in time, strip to his underpants, but alas, he will not get far beyond that barrier. He and Marjorie will be caught in bed, she naked, pulling at Arthur's knee-length drawers, while Arthur, the reluctant, anguished lover is romping with Eeyore, friend of Pooh.

This is the most overtly sexual moment in the novel. As the children grow older, sex becomes sublimated, and the flirtations are all with mystery, romantic kisses and the dangerous edge of life. What lurks beneath the friendships of the boys is unspoken. (A word only - "traitor" - is the accusation to Arthur when he abandons his friendship with a boy he calls his double. William Mainwaring, in order to pursue his obsession with a girl who is chronically ill.) With both his double and his triple. Philip Schoolcraft. Arthur seals the ties with potions of blood and wine, fingers pricked and the blood dripped into the glass. And with both boys Arthur plays the deadliest of games - Russian roulette - introduced to it by Philip, passing its pleasures along to William.

But it is Eleanor Schumann - the sickly girl whose absences from shool, whose empty desk, whose dreamy indolence when she does come to class, wholly captivate Arthur - who brings the book to its high point. Millhauser's writing here changes and becomes complex with repetitions and confusions of the real, the imagined, the remembered. Eleanor's marvelous toys (a juggler who can keep three balls in the air), her costume parties "in the sickroom she calls her tomb, next to the bed she calls her grave." Arthur becoming Pierrot for her, their masked ball of black death, their "marriage" and their plan to commit suicide witha draught of poison, their silent pursuit of one another through Eleanor's Children Museum with its dollhouse full of tiny life and spider webs, through her spectacular attic with its closets within closets which open into even more secret and mysterious rooms - all this is magically evocative of the secret, uncertain world that children hope to create with make-believe.

But Millauser is not always as magical as this. His novel is too long, too anxious to reconstitute every detail, however insignificant: ". . . erasing furiously from time to time and brushing away the eraser-dust with short sharp sweeps of the side of his pinky." A little of this goes a long way, and so does his repetition. Coming atop his anatomizing of the states and stages of youthful boredom, it often flattens us in the same way Antonioni's most boring films about boredom did years ago. And, too, some of Arthur's adolescent epiphanies are too familiar, or too unremarkable, to be saved even by Millhauser's linguistic felicities.

Nevertheless, his overall achievement is of a high order. The novel moves with relentless, if snailishly slow, logic toward a dreadful climax. And what we come away with is childhood without treacle, childhood mythicized, a poetically gothic history of living and dying in miniature.