"YOUTH," sighed Shaw, "is wasted on the young." Any writer d'un certain age must have similar emotions when he sees youthful talent squandered as recklessly -- and enchantingly -- as here by Fernanda Eberstadt, in her first novel. Low Tide is a slender sapling of a book, but it has enough sap rising to foliate an orchard. No doubt the time will come when Miss Eberstadt too will feel wistful for "the force that through the green fuse drives the flower." Her only problem now is to control this force, and channel it upward, rather than outward in all directions.

One does not doubt that she will succeed, because while Low Tide is mostly about passion, it is also about self-restraint. There is an austere, if overwhelmed intelligence behind the riotous sensibility. Her protagonists are young and very rich, yet they disdain drugs; they are beautiful and full of sex, yet they understand the value of chastity.

A glance at the back cover tells us the plot of the novel. Here, in profile, sits a graceful young woman. She looks both sensuous and devout. Huge eyes -- Spanish eyes; a plain gold ring. Five lines of copy drop the necessary words: New York, the Brearley School, Magdalen College, Oxford. Unsurprised, we begin to read inside about the large-eyed child of an East 94th Street brownstone, who goes to Oxford and meets a young man so extraordinary that she is "seized by a trembling crazy exaltation such as I had known only before God." The world around her, hitherto comfortably diffused by old money, leaps into focus and bright color, like an El Greco shoved in her face.

So far, so much Henry James. But James would not have called his heroine Jezebel, nor brought her to catharsis, fewer than 200 pages later, in Mexico. It soon becomes apparent that Miss Eberstadt's real mentor is Evelyn Waugh.

Jem Chasm ("You and I -- they named us both slave names," he tells Jezebel when bound to her) is demonstrably Sebastian Flyte, with his "tormented exquisite look" and eyes like "wet jewels -- eyes the color of an oil spill, petrol-green," his monochromatic clothes and eccentric diet -- bread and olive paste, chocolates and Armenian champagne -- his nimbus-like charm, which everywhere attracts a retinue, his monastic yearnings (Sebastian retreats to Morocco, Jem to Salamanca) and bouts of black depression, eyes "guttered out."

This is not to deny his originality as Miss Eberstadt's own creation. Jem is a sharper, more masculine personality than Waugh's epicene enigma, made flesh by a writer who is feminine to her fingertips. Uninhibited, she (or Jezebel) can rejoice in Jem utterly, and reveal her own soul in a succession of ravishing images. In their early days together, she feels "peeled to a new moon of myself." Separated from him, she sniffs a copy of Jeremy Taylor's Holy Living and Holy Dying for "any scent of Jem that clung to its leaves: a scent of black tobacco and starched cotton and steamed milk." Yielding to him eventually and inevitably, she feels him "pressing his way into my heart like a fish through the water."

It is Miss Eberstadt's imagery, indeed, that proclaims her a major talent. Waugh said of Wodehouse, "One has to call anyone Master who manages, on average, three quite original metaphors per page." Actually Waugh was exaggerating. Old Plum valued his currency too much to spend it so wastefully: and here is where Miss Eberstadt betrays her youth. She can manage three original metaphors a page -- sometimes in a single paragraph -- but she cannot suppress the lesser, to enhance the best. Her flowers are too copious and too various; the sapling bends under their weight, their combined perfume chokes us. On page 17, for example, we have several tarot symbols, then a Scarlet Whore, a boy with "buccaneer looks and wandering fingers . . . (and) a girl in every port," "late arctic light" in the middle of English summer, a mythical mother grieving for a soldier, and "books piled vertically in a shaky avenue of pagodas (that) looked as if they might walk away at night, leaving behind them unpaid bills." Of these images, only the buccaneer boy and the pagodas seem worth preserving, and even they should be further pruned, the former losing its clich,e and the latter its silly conclusion (pagodas do not walk, nor leave behind unpaid bills.)

PERHAPS it is unjust to select for criticism such a weak page, when there are so many more -- the majority -- that show abundant strength. Flicking at random, we come upon a rotting tree house "like a crazed aircraft pitched among the weeds," three Spanish sisters moving with "cheetah graces," Jem prancing down the Banbury road ahead of Jezebel, "doubling back like a kite on a string, recalled." We feel "words rising to the tongue like greedy trout," hear the "hot blurred voices" of Mexican construction workers "hanging like sloths" from a ceiling, and smell New York City's aroma of "festering flowers . . . crumbling leather, rum, and wet fur." Memorably, we watch the moon over Long Island, "hysterical and fugitive, streaming out its alarm, reeling in another direction from the clouds it flooded, like the instant's panic of automobile headlights on a wild road."

These images, lovely as they are, would not alone make Miss Eberstadt a novelist of rich promise. She has another essential gift: power of characterization. All the figures in this book are grotesques -- Jezebel calls them (and herself) low-tide creatures, "salt-dried, petrified in our monstrousness." She is wrong: they live and breathe lovably. Meet ageless Eustacius, her mother's Cajun cook, in his kitchen full of hot fetis; randy, Red- baiting Professor Chasm, who disappears beneath dinner-tables for serious conversation with children; Jezebel's art-dealing father, "this pink-and-gold flit"; old Mrs. Palafox, subsisting on black coffee and yogurt and "screeching her memoirs at the secretary." Most attractive of all is Jem's brother Casimir, the buccaneer boy, with whom we rather hope Jezebel will end up.

This reviewer looks forward to more novels by Miss Eberstadt. She will soon learn from Waugh that profundity is impossible without lucidity; from Molly Keane how to interweave humor and cruelty; from Thomas Beer how to combine color and speed; from Hemingway when to be violent (although her climax in this book is so well timed as to make the reader shout with alarm). And these older writers, or their shades, will learn again from her that there is nothing as beautiful as youth bursting with talent and love of life. CAPTION: Picture, Fernanda Eberstadt. Copyright (c) by Barry Lategan