50 By Avery Corman

Simon and Schuster. 254 pp. $17.95

AVERY CORMAN is a keen observer of middle-class Manhattan life -- he's Woody Allen minus the self-absorption -- who has somehow managed to keep part of his heart in what he called, in the title of his previous novel, The Old Neighborhood. He's aware that New York is still, after all these years, to a remarkable degree a city of people who came there from somewhere else -- not merely Kansas and Georgia, but also Brooklyn and the Lower East Side -- and it may well be this knowledge that permits him to see the essential shallowness of what passes for success in the Manhattan fast lane.

Whatever the explanation, Corman's satirical touch, his eye for nuance and his awareness of human frailties are what make his novels interesting. Strip them to the essence of plot, and there is not a great deal there: melodramas of romantic connection and disconnection, with a distinctly sentimental twist. But his stories are merely devices upon which Corman hangs the more substantial business of his novels: the development of characters who are both discrete individuals and vivid representations of certain middle-class types, and the deft, pointed annotation of the minutiae by which the precariously privileged seek to identify themselves.

Like Kramer vs. Kramer, for which Corman is best known, 50 is about divorce. The principal differences are that the ex-partners are about a decade older than the Kramers were and that they have agreed to joint custody of their two children rather than fighting over them in court. Otherwise, though, Corman again has his finger on all the grievances, petty and otherwise, that can arise between two people who once loved each other; beyond that, he is able to see the humor as well as the sorrow in marital disarray, which is why both of these books manage to transcend the tiresome conventions of the "divorce novel."

The formerly-marrieds in 50 are Doug and Susan Gardner. They split a couple of years ago: "When they were first married they were like a great balloon in bright colors floating over the city. Every year a little leaked out, small amounts one would hardly notice, until, at the end, there was nothing left." They have a 15-year-old son, Andy, and a 12-year-old daughter, Karen; their dog, Harry, is also jointly shared, in the spirit of middle-class enlightenment. Doug writes a column for Sports Day, a national newspaper in the USA Today mold, and makes about $50,000 a year; Susan wants to find a career in "the creation of store promotions," and as the novel opens is making relatively little money.

Doug is predictably, and understandably, bitter about this; he resents what he sees as Susan's dilettantish self-indulgence while he is tied to his job -- at 47, an age when one's options seem to diminish -- in order to meet his financial responsibilities to his children. This resentment grows as Sports Day is purchased by a Texan named Robby Reynolds, who "has the editorial judgment of a television programmer" and who delights in impressing upon his employes that he "owns" them; Reynolds is the embodiment of all the arrogant young cretins who have leveraged their way into the boardrooms of America, and Corman's depiction of him is all the more withering because there's not a hint of caricature in the character.

While Doug suffers under Reynolds' heavy hand, Susan goes off on her own and quickly makes a smash success as what Women's Wear Daily calls the "Rising Star of Store Merchandising." Suddenly she is paying her share of the children's expenses, and just as suddenly she remarries: to Jerry Broeden, who has made a small fortune in denim and is intent on enlarging it. Jerry is a creep -- the kind of guy who would look up to Robby Reynolds -- but he lavishes money and attention on his new family; the children, being children, fall for him, and Doug is crushed by the knowledge that "another man was in his place."

But funny things begin to happen in Doug's life, the exact nature of which will not be revealed here so as to keep your summer reading unspoiled. Suffice it to say that Doug develops a strong romantic interest in an exceptionally appealing younger woman and that after a confrontation with Reynolds, his career takes a dramatic turn for what seems to be the better. As a result of these developments Doug finds himself face to face with a couple of issues that, in the world of today's urban middle class, are not unimportant: whether, having had children in a first marriage, he has the energy and commitment to have more children in a second, and whether the startling rewards being paid in his altered professional circumstances are worth the price they exact from him.

ALL OF this takes place against the background of Doug's inexorable progress toward his 50th birthday -- an occasion that, as the novel ends, is just three days away. So not merely is 50 about marriage and divorce and feminism and fatherhood and loyalty to one's convictions; it is also about mortality, and the ways in which we become aware of it as doctors and others begin to talk about "men your age" -- the reading glasses, the muscle tears, the gray hairs, the lines on that face in the mirror. Further, it is about being cast back into the marriage market and finding a whole new generation out there, a generation to which your own world is utterly alien:

"Apart from the fact that Monica and her age group had no personal reference to World War Two, Roosevelt, Stalin, Churchill, Korea, the Kennedys, or Grace Kelly, she didn't know love is like a moment's madness either. After sex with one of these young bodies {Doug} was whimsically singing 'How Long Has This Been Going On?' and when he suggested it was one of the best ways of saying, 'I Love You,' in the history of popular music, the girl didn't know what he was talking about. You are babbling with them. They couldn't hum the verse to 'Stardust' if a Caribbean holiday on a game show depended on it, and they probably never heard of the Harry James solo from 'Sing Sing Sing.' They wouldn't know Irving Berlin wrote 'Better Luck Next Time' and they couldn't hum that either. How can you be involved with women who don't even know your songs?"

That passage nicely illustrates Corman's method: light, wry, a bit self-mocking, with the sadness and sense of loss just below the surface. He is a funny, perceptive writer who digs a little deeper than first impressions suggest. It would be easy to dismiss his novels as facile popular entertainments -- though they certainly are, and three cheers for that -- but there's more to them; they cut so close to the bone of middle-class life that they have far more to say than their unpretentious manner suggests. ::