Can a Fat Girl Find Love? : THIS IS YOUR LIFE: <i> by Meg Wolitzer (Crown: $17.95; 288 pp; 0-517-56929-9) </i>

Novels have a habit of disguising their true natures--sometimes even from their authors as well. Whatever the plot, whatever the setting, a certain subtext may insist on asserting itself, and this is the novelist’s true story, the one he or she will tell over and over, regardless of subject matter.

Of course, not every novelist is like this, but many of the better ones are. “Everybody has a theme, “ says a character in Meg Wolitzer’s “This Is Your Life”--”one particular thing that rules them. The best you can do is a variation on the theme, but that’s about it.” On the surface, Wolitzer’s third novel appears to be about the relationships between two sisters, their mother and the shadow of a missing father, and, yet, the real heart of the book seems to be the unknowability of others, the feeling that one is somehow not “normal” and the desire to be--or at least to appear--so, the same conflict between passivity/death and action/life that characterized the earlier “Sleepwalking” and “Hidden Pictures.”

But whereas those novels seemed content to remain in their rather claustrophobic worlds, “This Is Your Life” reaches out to broader horizons. The world of comedy, fame and its loss, its effect on one’s children--all play a part in the author’s most ambitious work to date. The mother, Dottie Engels, is not just any mother, but a cross between Joan Rivers and the late Totie Fields, a larger-than-life-size comedian whose shtick is endless self-deprecation. “I’m not ashamed to tell you that I married for money. My father said, ‘Here’s fifty bucks, Dottie, now get out of my sight.’ ” A smear of orange on her lips, garish red circles on her cheeks, polka dots (for “Dottie”) on her dresses, she is both horrifying and entrancing as she speaks the unspeakable in Las Vegas and on the “Johnny Carson Show” in order to make the world safe for the fat and “unattractive” everywhere. “My husband always hated it when I ate a huge meal before coming to bed. He said he had trouble falling asleep on a full stomach.”

But the story is not so much Dottie’s as her daughters’, as they try to exist with a figuratively and literally larger-than-life-size mother whom all of America adores. Whereas the younger daughter Opal, attractive and popular, one of the innate princesses of the world, wants nothing more than to remain forever the perfect audience for her mother, the older and less attractive Erica retreats into music, drugs and sex--this last with an unpopular 10th-grader whom she dates not because she likes him but because, with that peculiar teen-age awareness of power and status, she knows she can’t find anybody better.

This first part of the novel is terrific. Wolitzer is wonderful with children and teen-agers, their oddly stoic approach to life, the nurturing they offer their parents and other adults under the guise of being protected by them. Unlike the “shopping mall” novelists, Wolitzer’s candy bars, rock albums and sitcoms are not substitutes for characterization, but help illustrate the passive underside of what is generally thought to be a go-getting yuppie generation. Flipping the dial to see what’s on the air, her characters settle on a show the same way they choose their lovers, making the best of a limited field of available alternatives. It does not seem to occur to them to actually go out and achieve their desires--or even inquire into what these are--not so much because they have none, as because they have no faith that they could possibly be fulfilled.

The novel begins to lose its grip in the second section, after Dottie’s popularity has faded. In order to maintain the limo and the big Central Park West apartment, Dottie loans her name to the Dottie Engels Collection for Large Women. But if the ever-resilient Dottie can stand this--”Of course, I’d rather be opening at Caesars . . . but in the scheme of things, it’s somewhere between death and a few of the clubs I used to play”--Opal can’t. Her humiliation is so deep that she hides in her dorm room at Yale, cutting classes, until the dean forces her to take a semester off from school. Erica, meanwhile, lives in the East Village with that same prep-school boyfriend--now a cocaine dealer--refusing all communication with her family.

Although many of these individual scenes, written in Wolitzer’s usual pellucid style, are effective, much of the story is unconvincing and unbelievable. As in the soap operas that Wolitzer’s characters watch and listen to, coincidences and melodrama abound--Opal, sent to pick up cocaine for an actor in the TV show for which she works as an intern, finds herself in Erica’s apartment; her fellow intern (and future lover) seems to be in the background of a childhood photo of Opal taken at the World’s Fair; Dottie suffers a heart attack while making a comeback appearance on a TV game show.

After the fall, there’s usually redemption. The final part of the novel, involving Dottie’s recovery via a weight-loss program, the reunification of the family, and the salvation--via decent relationships with men--of Opal and Erica, seems perfunctory, sentimental and forced.

But this is one novel that is better than its plot. Indeed, at times one feels that the action is there merely as a pretext for the characters’ perceptions. Thus, although Dottie’s rehabilitation is clearly a plot device to facilitate the novel’s reconciliatory climax, the fact that Erica’s acceptance of her own fatness is concomitant with her mother’s forced shedding of it rings absolutely true. In addition, with Wolitzer’s narrative technique, which involves a succession of rather static scenes that depict not so much events as the states before and after the events, individual scenes can remain compelling and unconvincing even when the overall structure falters.

Finally, the basic metaphor of the novel--the relation of oneself to one’s body and those of others as a symbol for the way one relates to the world--is a highly powerful one. Considering the obsession of our culture with fatness--or, rather, thinness--particularly the fatness and thinness of women--and to what extent the subject is dealt with in women’s magazine and how-to books, it is odd how rarely it is addressed in serious literature. Wolitzer evokes a compelling vision of fatness as an expression of a profound ambivalence of the self concerning its dual desires both to assert itself and to disappear.

The dichotomy, I believe, lies at the heart of Wolitzer’s writing, and gives it its peculiar resonance. Always in her books there tends to be a sense of distance from life, a kind of hushed, albeit compelling airlessness in which the characters float like zombies across the thick carpets of their air-conditioned rooms, strangers from another planet, so fatigued by their efforts to appear human and connected that they neglect such ordinary matters of life as exchanging summer addresses, playing sports or having hobbies.

Wolitzer’s characters, in this novel, actually manage to crack the bell jar in order to enter the real world outside. It’s a big step forward, not just for the characters but for the author too.