"DIVORCE," according to Nora Ephron, "is essentially the major subject of American novelists." This as it happens is not true, but there are times when it certainly seems to be -- especially if one limits one's reading to those novels and stories written by the bright, sophisticated, witty middle-class women who in the past decade have become a considerable force in American fiction. Because marital strains and dislocations are so much a fact of contemporary middle-class life, it is scarcely surprising that they should be so much with us in contemporary fiction; but by now there seems precious little left to say on the subject.

Thus it is that familiarity is the principal weakness of In the Palomar Arms, a novel that in most other respects is appealing, literate, intelligent and sensible. Here we go again: Married man lives in handsome Los Angeles house with beautiful wife and adorable children, but marriage has lost its original zing; married man meets sensuous, 24-year-old college student, begins passionate affair; married man tells lover he will leave wife and kiddies for her; married man, after much delay and uncertainty, announces plans to wife, who promptly goes the extra mile in retaliation; married man is in quandary, torn between love and passion on the one hand, duty and loyalty on the other.

This is not intended to oversimplify the contents of Hilma Wolitzer's latest novel nor, least of all, to condescend to it. I've greatly admired her work since the publication nine years ago of her first novel, Ending, and In the Palomar Arms does nothing of consequence to alter that admiration; she writes clear, pleasing prose, she adamantly refuses to sentimentalize her characters or to allow them easy answers to life's difficulties, and she has as sensitive an understanding of the nuances of domestic life as anyone now writing. But you just can't get around it: the central situation in this novel is a cliche, and none of the subplots that Wolitzer erects around it can disguise its familiarity.

The man is named Kenny Bannister, his lover is Daphne Moss. They're nice people: Kenny is a notably successful tax accountant who does love his two young children, and his parents-in-law, and sometimes even his wife; Daphne, when she can bring her fuzzy mind into sufficient focus, offers affection and cheer to the old folks at the Palomar Arms, a "convalescent and rehabilitation facility" where she works. "There had been a time right after he and Daphne met when Kenny fleetingly considered that he was too old for the hardships of courting," but that moment quckly passed: "He discovered that he had no choice. Desire propelled him into action, overcoming logic, and his energy was renewed.And of course it was worth it; it was worth anything."

But this is the main question posed by the novel: Is love really worth anything? Is the passion that Kenny feels for Daphne of greater consequence than the ties and allegiances of his marriage? Daphne, who is smarter than at first she seems to be, puts it to him this way after a visit to her home in Seattle:

"In my parent's house, . . . I looked at all the things they've accumulated over the years -- pots, colanders, photographs, canceled checks, place mats, tax returnes, plants, the things in the medicine chest and the kitchen cupboards, the marked boxes in the garage and the attic . . . clothing and tools and yearbooks and letters. I realized that you're bound to your family by things, by possessions and experience, even by the bad times. You and I were good together, Kenny, but we hardly have any history between us. And history always wins out in the end."

Or, as Laurie Colwin puts it in a fine story called "Swan Song," published last month in The New Yorker: "Married people suffered and rejoiced over and over and over and over again. Marriage was a trench dug by time, a straight furrow, the mighty oak that has grown year after year after year from a tiny acorn.Lovers were, by comparison, little scratches in the ground." In sharp contrast to the novels of the 1970s, in which Erica Jong et al. led their heroines out of the confines of marriage into the freedoms of separation and divorce, these thoughtful writers bring their women -- and their men -- to the edge of divorce and then make them face the full import of it. It's a new twist, and it's elegantly turned, but it's still and old story.

The principal subplots with which Wolitzer embellishes that story involve two of the residents of the Palomar Arms: Nora McBride, whose 100th birthday supposely is approaching (it's actually her 98th, since she lied about her age eight decades ago and has stuck to the lie ever since), and Joseph Axel, a newcomer to the nursing home. The old woman ardently fights to live on, the old man is eager for the escape of death; but both, as they tell Daphne about their lives, give her a deeper awareness of what she meant when she talked about "history." And in the Palomar Arms, as she listens to "older people say they don't envy the young their sexual freedom, that they wouldn't be young these days for anything," she arrives at another moment of understanding:

"Suddenly, in her awful wakefulness, Daphne knew what the older people meant. It was that the old-fashioned idea of abiding love -- what her generation called commitment -- was endangered by the ease of casual sex. The faithful mind and the wanton body were only mortal enemies confined to the same prison. Did one always have to perish for the other to survive?"

That's good -- like much else about In the Palomar Arms. Wolitzer writes about the old people of the nursing home with real affection; there are several lovely vignettes, in particular a shopping expedition that Daphne and a friend undertake in the boutiques of Rodeo Drive and Kenny's first conversation with his no-nonsense divorce lawyer; throughout the novel, Wolitzer maintains a sensitive awareness of the value of life balanced against the ever-present reality of death. But apart from the familiarity of its subject and the people affected by it, the novel has other weaknesses. Its point of view shifts too often, from Kenny to Daphne to Nora McBride to Joseph Axel, with the result that there is no real center, or focus, to it; and the character of Joy, Kenny's wife, is sufficiently unappealing that the reader, if not the author, can't help asking if this marriage is really worth saving.

By comparison with most novels in the divorce genre, In the Palomar Arms is subtle and sensitive. But the inescapable fact is that it never manages to rise above genre, that for all the abundant skills Wolitzer brings to it she merely retells a twice-told tale; it's a great pleasure to read In the Palomar Arms, but at the end what you know more than anything else is that you've been there before. CAPTION: Picture, Hilma Wolitzer, Copyright (c) 1983, by Thomas Victor