Ho hum, more Neil Simonizing. "Only When I Laugh" assures film-goers that the Barry Manilow of the written word is still alive and well, still struggling with human relationships, still finding them beyond his feckless penmanship, still plumping them up with snappy patter. He's taking no chances with the formula.

As usual, there's a terminally urbane cast of New Yorkers: James Coco as the quintessential gay man, Marsha Mason as the oral compulsive with a heart of cold, Joan Hackett as Elizabeth Arden's best customer, and Kristy McNichol as the pert and adorable child-woman who, with a key word here, a key look there, rights the lifestyles of this trio of inept oldsters.

In "Only When I Laugh," Mom joins Pop in being dumber than the dog and the kids. It's a cosmic Kool-Aid high for Kristy McNichol fans, who'll find her warming up the "Family" leftovers as the daughter of Marsha Mason, a self-absorbed alcoholic and former fat lady.

McNichol is the psycho chic, modern child inheriting the bequests of "Kramer vs. Kramer," "An Unmarried Womanc and "The Goodbye Girl." Mother and daughter relate over Tab and Haagen-Dazs. They are realistic. They share angst. Could Shirley Temple have coped if Jane Wyman had been beaten up by Adolphe Menjou in a tawdry back lot at MGM? No, America's little miss would still be shrinking her itty bitty brrains trying to get over it.

Psychodrama. Where would the movies be without it? Motivation's made simple. A good shrink scene explains everything without unnecessary dialogue. The shrinks don't say anything, making that part pretty easy on the author. The patient, in this case Marsha Mason, gets it all out, tells it like it has been, barraging us with a stream of consciousness, as the credits play. This time she hopes it works, she says to the comely, kindly scion of the subconsious, and the autdience is launched into a two-hour morality movie on the compulsions of the upper-middle class.

Marsha Mason, dried out, thinned down and made up to look like death warmed over, is picked up at the Long Island hospital by Joan Hackett, who is perpetually concerned with aging and its effect on the beauty process. Hackett whisks her to her shabby apartment on the Upper West Side where the chubby, feisty, semi-flitty James Coco arranges flowers, bagels and lox for the occasion. Everyone keeps telling Mason, who plays an important actress who's spent everything on this transformation, how great she looks; she must have looked a sight before she went to that hospital.

As the plot quickens, the daughter, who's been living with Dad in, one guesses, Westchester County, meets her mother the very day she leaves the hospital and asks if she can move in for a year. Mom still has her cigarettes, which she sucks profusely, and she figures she can cope. McNichol moves in. In a meaningful moment, Mason and McNichol go on a shopping spree and are nearly picked up by two college boys who mistake Mason, who is supposed to be 38 but looks 50, for a senior in college. Alas, Mom's had an unhappy love affair and opts against a double date.

However, she does decide to double her load of day-to-day pressure by doing a play written by her ex-lover, an important playwright, about their depraved lives together. We wait for her to break down, to eat a chocolate pie with a Miller Lite chaser. And suddenly, "Only When I Laugh" becomes "I'll Cry Tomorrow." Mason walks past the neon signs, passing up Bud, Bar and Cocktail Lounges. Susan Hayward she isn't, though later she admits she'd like to have been if she'd had it all to do over.

Finally, mercifully, Mason goes for the gusto. Tee many martoonies later, she's sloshing booze all over the satin upholstery at Hackett's house. By now, the pictures on the plush penthouse walls become terribly interesting. This cocktail partyhs gone on too long and the patter's wearing thin. Down the hatch with this one.

ONLY WHEN I LAUGH -- At 10 are theaters.