20 UNDER 30: Best Stories by America's New Young Writers. Edited by Debra Spark. Scribner/Signature. 269 pp. $15.95; paperback, $7.95.

HERE, WE ARE to believe, is the future: 20 short stories by American writers under the age of 30, writers among whom, according to one blurb on the jacket, "are the master storytellers of the 21st century." That is a rather extravagant claim, and there is not a great deal in 20 Under 30 to substantiate it. There is, on the other hand, a considerable amount of accomplished writing, and a few of the stories actually do make the reader sit up and take notice. Whether any of these people will mature into writers of the first rank is both problematical and immaterial; there is enough capable work here to make 20 Under 30 interesting in its own right.

The authors are for the most part uknown; unfortunately, no brief biographies are supplied. David Leavitt we know as the author of the well-received story collection Family Dancing (from which "Aliens" is taken for this volume), Susan Minot has published in The New Yorker and has a first novel coming out next month, and David Updike, who has also published in The New Yorker, is both blessed and burdened by being John Updike's son. But who are, among others, Kate Wheeler, Michelle Carter, Ann Patchett and Michelle Herman? It would be nice to know; they have done provocative work.

What we are told about them by Debra Spark, the editor, is as follows: "The authors' ages in the collection range from twenty-one to thirty. They are all Americans. Few are married, fewer still have children. Many are, or recently have been, associated with universities or writing programs." Sparks calls "this last fact . . . an accident and not a particularly happy one," but on the first count at least she is entirely wrong. There is nothing accidental about the predominance of stories from the universities, since virtually all work by young American writers is now done in the womb-like conditions of the writing programs; the real surprise would have been if a noteworthy percentage of the stories had come from elsewhere.

The influence of the classroom is most evident in the prose of these writers, which is always competent but hardly ever distinctive. That all 20 of these people can write is beyond dispute; yet there is neither an original nor an urgent voice among them. Had the collection been presented as the work of a single writer, most reviewers and readers probably would have greeted it as "promising" and then praised the author for making a deviation or two from his customary cool, distanced, low-keyed style. But there really are 20 different people here; the problem is that they've all done the same homework, boning up on Carver and Beattie and Barthelme and the other gurus, so it's hardly surprising that they sound eerily alike.

Nor is it surprising than many of them are preoccupied with the same or similar subjects. This, though, has less to do with the writing schools than with their youth and their common experience. Not one of the stories is overtly or covertly political; unlike the young writers of the previous generation, who had been shaped by Vietnam and campus tumoil, these writers for the most part look inward. Many of the stories are about families, many of which in turn are disintegrating, and often the point of view is that of a child or adolescent. There's a fair amount of craziness, alienation and anomie, which are fashionable in certain circles but which also are characteristic of young writers in any period. There is also, as is inevitable in apprentice fiction, some wide- eyed discovery of life's larger truths and unpleasantries; as Lorrie Moore puts it, "Someday, like everybody, this man you truly love like no other is going to die. No matter how much you love him, you cannot save him. No matter how much you love: nothing, no one, lasts."

FOR THE MOST part the stories seem more manufactured than inspired, but there are three gratifying exceptions in which pure imagination is vigorously at work. The longest of these is Michelle Herman's "Auslander," in which a 34-year-old woman who works as a translator is drawn against her will into the domestic entanglements of an extravagantly gifted Romanian poet and her peculiarly protective husband; it is a story of considerable depth and power, one that investigates the sources of art and conflicting human loyalties with intelligence but without belaboring its themes. Another accomplished piece is "All Little Colored Children Should Play the Harmonica," by Ann Patchett, a gentle, whimsical and pointed story about a black schoolboy who'd rather play music for himself and his friends than for the white schoolteacher, even if it means forfeiting a chance at a considerable musical career.

But the best of the 20 stories, to my taste at least, is Leigh Allison Wilson's "The Raising." The childless Mrs. Eastman is "a specialist in armchair mothering," a domineering and foolish woman who "had a gift of activity at its most inessential whereabouts, a kind of feverish sprinting in place that left her wrung-out and as blind as a newt"; her husband "wanted to pat his wife kindly on the cheek or else smack her very hard in the middle of her face." Now she is about to have a boy in her house, Little Darryl: "He was thirteen years old, of a conspicuous unknown origin, and he had lived in nine separate orphanages, one of which burned down mysteriously." What comes to pass is an encounter between innocence and evil, with results that are at once hilarious and devastating. The comparisons to be drawn are with Welty and O'Connor; Wilson looks for all the world like a born writer, one who has real stories to tell about real people.

How many others among these writers have been blessed with that gift? It's too early to tell. As a group they seem talented but cautious, content to stay within themselves rather than take risks. Neither do they, as a group, have very much to say; not many of these stories are insistent, demanding to be told. It's a pleasure to read their work, no doubt about that; yet that pleasure quickly becomes a blur, with only a handful of the stories sticking in the memory. If there are any "master storytellers" here, it will be some time before we learn who they are.