Scar-Crossed Lovers : A THOUSAND BENJAMINS <i> by Michael Kun (Atlantic Monthly: $18.95; 384 pp.; 0-87113-345-8) </i>

Mary Jude Sacks can’t take it any more, and, after 20 years of marriage, she finally walks out on Benjamin Sacks, the inert, self-pitying, childhood-tormented hero (he’s 41) of Michael Kun’s first novel.

On her way out of their Baltimore apartment, Mary Jude explains to her gloomy and depressed husband (he spends most of his time on his living-room recliner) that “You just don’t make me happy any more, Benjamin. A thousand Benjamins couldn’t make me happy any more”--a sentiment, indeed, with which wise readers will concur, envying Mary Jude her freedom to walk out the door, and hence out of these many maudlin and maundering pages.

It isn’t that Benjamin (and his older brother, Phinney, who plays a part here too) doesn’t have his problems; instead, it’s that one can’t help but feel these to be problems that are old and worn and bygone, and that are summoned up now in the service of a dour-toned and artificially portentous staging that’s the real motivating purpose of this, at heart, jejune and soap-operatic novel.

Benjamin and Phinney’s father, hyperactive on the imagination side, was apparently prone throughout the boys’ childhood, both to elaborate tale-spinning and to the burst forth energetically with slightly crack-brained ideas and projects.

And so it came about, back in that awful summer of 1963 (the turning point in Benjamin’s life, about which he now broods endlessly, finally driving Mary Jude away), that father Sacks took it into his mind to dig a well in the family’s back yard. And so it came about, too, that mother Sacks one day by chance tumbled into the unfinished well, died a lingering death and was followed soon after by her faithful husband. He had joined her in the state of eternal bliss by jumping off the hospital roof, leaving his two teen-aged sons (Phinney was to have a complete breakdown and be institutionalized for some time) to be reared by one Mrs. Magruder, a friendly but not intellectually gifted next-door neighbor.

The comedy implicit in this folly-laden old tale is not, happily, lost entirely from Kun’s view, and some of his best pages and passages grow out of it, particularly those portraying Benjamin’s summer jobs that year. But, in general, that faintly clownish moment of long-ago tragicomedy is made of a frail little pedestal of clay that’s asked to hold up the huge, inert, Angst -loaded mass of Kun’s present-day and forebodingly “meaningful” novel, a little bit as though Salisbury Cathedral were to be mounted on a foundation of Tinker Toys.

One result of this vast disparity in tone between cause and effect (the effect ostensibly being, in the novel’s foreground, Benjamin’s present-day depression and emotional paralysis) is, of course, enormous sentimentality. As if fully aware of the very shaky grounds for Benjamin’s vast and overwhelming sorrow and Werther-like Weltschmerz , the author drums it up, insists on it over and over, makes dramatically hollow claims for it again and again, and gilds it shamelessly. As narrative, the book becomes meretricious and too often embarrassing, and one comes to find in the unprepossessingly traumatized character of Benjamin himself less a groping thought-hero than a walking boy-man with a case of arrested sexual-emotional development, American style.

After Mary Jude walks out on him, Benjamin keeps on eating his Fig Newtons (he loves them), taking his prescription tranquilizers (says he once, as he does so: “Please, God, don’t let me cry”) and being very, very sad. He does, however, manage to pick up a bright, bubbly, perky, 23-year-old Japanese-American waitress named Kim (“She had seen something in the restaurant, Benjamin thought: my loneliness”), who soon moves into his apartment.

Fair enough. What might be a normal and life-bracing arrangement, however, must first be transformed into requisitely bittersweet fuel to help feed the massive, dread-and- angst- producing engine that actually propels this fundamentally shallow and yet relentlessly and fashionably stultifying novel. So it is that Kim, you see, just won’t take off her shirt (she lives in T-shirts), and, when Benjamin forces the issue, he finds out why: She has a large, disfiguring scar from--yes, from emergency, life-saving heart surgery that she’d undergone not long before, as a teen-ager.

Kun’s, it seems, is indeed a novel of the walking wounded--Benjamin is scarred; Kim is scarred (near the heart--get the parallel?); Phinney is scarred; for that matter, Mary Jude doesn’t hear so well out of one ear, and even the man who ends up marrying the kindly Mrs. Magruder is missing an arm.

Benjamin himself earns a thousand negative points in the reader’s view for manliness and kindliness in his response to Kim’s creek-like scar (he’s repulsed by it, and sex comes screeching to an end). But there’s no doubt that his revulsion provides him with a new string of worry-beads that he can fret over for the many pages that follow (“Maybe I don’t want to touch Kim, he thinks”; “It’s the creek, he thinks”) as he and Kim drive out to Nebraska to visit the fragile-as-an-egg Phinney (“Do you know anyone who isn’t miserable?” he asks, “I mean, anyone our age?”), then bring Phinney back to Baltimore with them to a domestic apartment-trio and to a story’s end that, however unwholesomely, and with double doses of saccharine, lets the infantile and woman-pampered Benjamin have his cake and eat it too.

Woman-pampered? Well, that’s just part of the whole script. As unreal and psychologically ersatz as anything else in the book is Kim’s blithe and saintly failure (“this happy child dressed like a Japanese doll”) to turn in rage on Benjamin’s piercingly self-absorbed, sexual caddishness.

Or consider Mary Jude’s otherwise wholly inexplicable request, after giving Benjamin 20 lost years of her life, and with one foot out the door as she flees to salvage her own: “God, Benjamin, promise me you won’t ever change?” What? You mean grow up? Perish the thought.