The Janes Versus the Johns : TWO GIRLS, FAT AND THIN, <i> By Mary Gaitskill (Poseidon Press: $18.95; 304 pp.)</i>

In Mary Gaitskill’s universe, the war between the sexes is not a frothy comedy starring Katherine Hepburn and Spencer Tracy but rather a grainy, unsentimental documentary meant to make a point about violence against women and the equally disquieting need some women feel to be debased and humiliated. It’s the pimps, johns and sadists versus the women, who don’t like playing opposite these creeps but aren’t sure what other roles are out there.

Gaitskill’s 1988 short-story collection “Bad Behavior” was a daring, disturbing and impressive first work of fiction about an unsavory crowd of New Yorkers. The time is now, the drugs are plentiful, S & M is in, sex is for sale, and the dialogue is nasty, brutish, short--and often darkly witty and ironic. “You’re not really a masochist,” complains a sadistic man to his partner in a story called “A Romantic Weekend.” Her answer: “Maybe not. It always seemed like I was.” In one chilling story, a teen-ager working as a secretary is molested repeatedly, with spankings, by her boss.

Gaitskill’s women aren’t exactly lovable, but they engage us because they long for more than they’re getting, and because, as children, like the rest of us, they were given dizzyingly contradictory messages about what men expected of them. One woman remembers being in her father’s study when she was 12, rubbing his neck, and noticing his Playboy pinup calendar on the wall. “ ‘Do you like her?’ she asks, referring to the woman in the picture. ‘Sure I do.’ ‘Would you like to meet her?’ He looked shocked and said, ‘No, she’s just a dumb broad.’ ”

Gaitskill’s first fiction was the work of a bold, skillful writer in command of her material and her gifts. But in moving from short stories to the novel, in “Two Girls, Fat and Thin,” she seems to have lost her bearings.

If her short stories are precise and economical, her novel is overinflated, as if she is not sure what to do with all the pages she must fill. Characterizations are unwieldy, dialogue is merely functional, which is to say bland, and Gaitskill’s gritty, sharp-edged sensibility has gone into hiding.

Instead of insight and irony, she dishes up sentimentality along with a cult philosophy called Definitism, about which I would be hard-pressed to say anything definite. Nor could I tell you where Gaitskill stands on Definitism or its fictional guru, novelist Anna Granite. Does Gaitskill admire Granite or does she think Granite and her followers are as fuzzy-headed as they are likely to seem to her readers?

Narrator Dorothy Storm, 34 and fat, works the graveyard shift as a proofreader for a Wall Street law firm. As a teen-ager in Painesville, Pa., she was sexually abused by her father. Answering a journalist’s query in a Manhattan weekly, she meets free-lance writer Justine Shade, “a neurotic, antisocial twenty-eight-year-old” who has developed a sudden interest in Granite and intends to write an article about her.

Both “girls” grew up in the Midwest, and Justine also was sexually abused as a child, by a friend of the family. Dorothy answers Justine’s ad because 15 years earlier she worshipped and then worked for Granite, who is now dead.

In Dorothy’s words, Granite “was a great writer and she spoke with a Romanian accent. If you have a woman with all those qualities saying ‘Hello’ to you, it’s an event.” She recalls her first Granite lecture: “I remembered myself so overwhelmed by the emotional current unleashed by Granite, as well as by the exhaustion of finding myself in the middle of my dream world, that I could only comprehend Granite’s speech in fragments. She talked about the tragedy of the individual being sacrificed for the weakness of the majority . . . I wept for the entire time, deep in the turbulent waters of my rampaging feelings . . . I wept with rage, yet with decorum.”

In alternate chapters, Gaitskill recounts Dorothy’s and Justine’s childhoods as well as Dorothy’s stint working for Granite. In tedious detail, she summarizes--rather than bringing to life through dramatization--the harsh suburban lives that led the women to their dysfunctional New York adulthoods. A typical passage:

“Those dinner tribunals occurred with such frequency that I developed the ability to divide myself while they occurred; the external person who sat and cried while her father reviled her and the internal person who helped herself to more salad as he ranted, and noticed that the scalloped potatoes were particularly succulent tonight. With bitter pride I hugged the inner me to myself at night and thought how I had enjoyed dinner, no matter what. But my pride was marred by the dim awareness that it sometimes felt as though it was the external person who ate her dinner in dignified silence while the internal person hurt.”

As an adult in New York, Justine “swam through the day just below the surface of mental alertness, bumping her head on the floating detritus of impressions and thoughts.” She writes her article about Granite, takes up with a sadistic man, and she and Dorothy end up soul sisters, consoling one another for all the abuses they’ve suffered at the hands of sadistic men.

Laurie Colwin once used an ice-skating simile to compare writing short stories to writing novels. With a novel “you have more room. It’s like getting onto the ice in a huge place. . . . You’ve got the whole pond to yourself. You can do anything you want. A short story is like being on a tiny patch of ice--one of those little training rinks where you can circle a couple of times and that’s it.”

In her short stories, Mary Gaitskill did far more than circle a couple of times, and one hopes that in her next novel she will feel more comfortable having the whole, huge pond to herself.