THE NOVELS of Rona Jaffe, of which Mazes and

Monsters is the 10th, suggest nothing so much as a severe case of arrested adolescence. They strive for satire but achieve mere innocence; they are crammed with authentic detail about the bric-a-brac of upper-middle- class life, but reveal little sense of what any of it means; they are composed in a gee-whizzical prose that would be exactly in its element at a high-school slumber party.

That Jaffe has achieved a considerable readership over the years is not especially surprising; her novels are chatty, breezy, mildly sexy, utterly undemanding. To the reader who finds Cosmo the ultimate in sophistication, they doubtless seem as worldly as the journalism of Rona Barrett and as profound as the theology of Steven Spielberg. They fall somewhere between the novels of Jacqueline Susann and the stories of Laurie Colwin-- neither as brassily trashy as the former nor as slickly literate as the latter.

What is rather more surprising is that over the years Jaffe has been given a fairly respectful reading by book reviewers. Her previous novel, Class Reunion, a book of singular emptiness, got what the publicity departments like to describe as coast-to-coast raves; the jacket of the paperback edition is decorated with shimmering encomia, some of them delivered by people and publications that should know better.

Certainly Jaffe's novels are amiable enough; perhaps this is what has seduced the readers. But her books are also transparently simpleminded. Mazes and Monsters is a case in point. It manages to be trendy and sentimental at the same time, in the grand tradition of Erich Segal; beneath its ritualistic recitations of brand names and its giggly ventures into the caves of evil, it's just another inspirational story by a novelist who resolutely believes that the highest purpose of life is to scale the next rung on the ladder and that tomorrow really will be better.

The title refers to a game (bearing a strong resemblance to Dungeons and Dragons), popular on college campuses, around which Jaffe has fashioned her plot: "Played with nothing more than a vivid imagination, dice, pencils, graph paper and an instruction manual, Mazes and Monsters is a war game with a medieval background, in which each player creates a character who may be a fearless Fighter, a treasure-hunting Sprite, a magic-using Holy Man, or a wily Charlatan. The point of the game is to amass a fortune and keep from getting killed." Which sounds a lot like the point of life on the Upper East Side.

The players in this particular game are students at Grant University in Pennsylvania.heir names are Jay Jay Brockway (poor little rich boy from Manhattan), Kate Finch (tough but oh-so-vulnerable beauty from California), Daniel Goldsmith (Jewish computer genius from Massachusetts) and Robbie Wheeling (shy, handsome, troubled Connecticut suburbanite). They play the game fiercely and endlessly, but it's only a game . . . or is it?

Of course it isn't. Jay Jay, in search of higher thrills, sets himself up as Maze Controller (God, as it were) of a new game, this one a real encounter between real people in real caverns that the college has ruled off-limits to students. One thing leads to another, until . . . but you can fill in the dots for yourself, if you really have the time and inclination. Suffice it to say that fantasy and reality become hopelessly confused and the novel becomes hopelessly melodramatic. But three of the kids do learn their lesson:

"The odyssey they had just been through had been their transition to real life. They didn't need the game to be friends, or for anything else. Maybe they had once, but they didn't need it now."

It is difficult to come up with a more obvious moral than that one, but for Jaffe it clearly has the stinging clarity of divine revelation. But then, almost everything does. She trips through her novels in wide-eyed, dopey amazement, seeing all with born-yesterday wonder and recording her observations in a prose that would make Holden Caulfield wince:

"She thought how much she would really like to go to Europe with her two lifelong friends, the places they would see, the adventures they would share. She couldn't bring Robbie if they didn't each bring a man because she'd always have to be with Robbie and it wouldn't be the same. She thought guiltily how being in love made you so committed; you couldn't go off with other people for a long period of time because you missed the person you loved, and knowing he missed you made you feel like a rat."

The thought occurs to me that, here and in countless other similar passages, Jaffe is aiming for irony; but I think not. She is just plain too damn . . . sincere. She loves to wish herself back to those good old college days; wishing herself back to college is what Class Reunion was all about. When she prattles like a bubbleheaded teenybopper in the most wretched throes of grand passion, she's not mocking; she's in her true voice.

Like the other Rona, the one on television, Rona Jaffe fancies herself a sophisticate; she knows all the right names and where to drop them. But neither her New York City birth certificate nor her Radcliffe diploma can disguise her abiding innocence; even if she'd been born in the Cafe Carlyle, during Bobby Short's second set, she'd still be country come to town.