Reconcilable Differences : SILVER <i> by Hilma Wolitzer (Michael Di Capua Books/Farrar, Straus & Giroux: $18.95; 352 pp.; 374-26422-8) </i>

One August Saturday, lying next to her husband Howard in the air-conditioned hum of their Long Island bedroom, Paulette Flax decides to leave him. That very night, Howard has a heart attack. As they stumble half-dressed through the house, headed for the hospital, she silently orders him not to die: “We have unfinished business, you bastard.”

Paulie suspects an affair. This time, she’s told herself, she hardly cares. But with Howard slumped against her, Paulie realizes, “Suddenly I wanted to know who she was, and how it had happened, and why. Had there been others? I was afflicted with jealousy; I’d forgotten its stunning pain, the way it rides the lining of the body. . . .”

The subject of “Silver” is love, sustained; in this case, for 25 years. But the very prospect of their silver anniversary dissolves the marriage. Paulie can’t bring herself to celebrate a union so tarnished.

While Howard and Paulie become un-married, they work hard to marry off Jason, their wandering drummer son, to the expectant Sara, a.k.a. Flame. (She is the very-well-brought-up lead singer with his rock group. Her pink hair stands up in spikes, but she writes thank-you notes like nobody’s business.) This is history repeating itself: Jason’s arrival occasioned his parents’ own marriage.

Paulette and Howard Flax have lived in two worlds of fiction. They first appeared, as newlyweds, in Hilma Wolitzer’s novel “In the Flesh.”

“These two have lived in my head so long they ought to pay rent,” Wolitzer writes. Paulette and Howard are fresh, frank, funny and smart, and their voices are nicely individuated. They tell the story of their marriage in alternating chapters. His ‘n’ Hers.

Listen to Howard. He’s a jazz musician, the proprietor of a recording studio. When he thinks about death, he thinks of his saxophone, “shining away right now in its dark case in the dark hall closet. I would be like that, without music, without light.”

Paulie’s voice is clear, nervy and without illusion. Her plans for self improvement--the poetry workshop; the notebook to be carried everywhere--are long abandoned: “I never got around to any of that . . . .”

Instead, she works part time in the local library and writes a newly syndicated column, “Paulie’s Kitchen Korner.”

She is the daughter of a reckless speaker: Her mother promises, “If you love each other in your hearts . . . you can work the rest out. You have your whole lives to do it in. And life is short.”

In the quiet Long Island hospital, Paulie thinks about hospitals in the big city, “jumping on Saturday night,” with people overdosing “on everything from crack to vanilla extract,” and she is wistful: “Oh, why did we ever move?”

When Paulie leaves Howard and sublets in the city, there are some nice Manhattan Moments. Her best friend’s husband confronts her at 10 in the morning: “Well, aren’t you going to invite me in?” he asks. Paulie is still in her bathrobe. “As we stood there, the woman who lived across the hall came out of her apartment. She pressed the elevator button and leaned against the wall, gazing at us with leisurely, open curiosity.”

The city, with its proofreading jobs, the riches and quiet of libraries, the poetry workshop at the New School, and a lovely man named Bernie, is Paulie’s salvation. There she discovers she is not a poet, but a writer of prose. In the city, she grows and finds strength--which Howard calls “that creepy new composure.”

Yet Howard shrewdly senses that the marriage can be saved. As in some Elizabethan play of doubles and double marriages, a condition must first be met. Howard must bring Jason back to Sara/Flame. When he succeeds, “something like music kept rippling through me.” Howard has made his own bliss.

Paulette was right to dread the anniversary party. Parties are difficult to write. This one is a less-than-perfect end to an amusing book.

Population is a problem. One must have people for a party, more people than are convenient to contain in a novel. So, in the final pages of “Silver,” the ranks are swelled by a bartender and two waitresses, by Jason, sulking stoned in his old room, by Sara/Flame’s parents, by an old friend’s old friend, by “a beautiful black woman named Trish,” by Howard’s cousins, the next-door-neighbor’s younger daughter, and the new baby, Byron. The book and the house are jammed.

The end of the narrative is stuffed with last-minute references to Jane Austen, to Hemingway’s Brett Ashley, to a marriage counselor named Dr. Lewin, to a look-alike couple carved in stone on an Etruscan sarcophagus. Even Mendelssohn’s name pops up. Wolitzer gives it everything she has.

Is this the breakthrough novel its publisher hopes? Yes and no. “Silver” is Wolitzer’s fifth adult novel. It should bring her a wider circle of readers and new acclaim.

“Silver” is a selection of the Literary Guild; an ABC-TV movie-to-be. Its first printing of 75,000 books is matched by an advertising budget of $75,000, and a floor of $150,000 has been established for the paper auction. In the financial sense, this is a breakthrough novel.

But “Silver” as an artifact--despite its charm, despite its two engaging characters--is somehow unfinished and messy. It is more like a household object than a literary one. “Silver” has the homely and rumpled look of an unmade bed.