Spontaneity doesn't come easy to an incorrigible gag writer like Neil Simon. The typical conversation in a Simon play is more suggestive of professional comedians trading quips than ordinary human beings in unrehearsed give-and-take.

The pattern persists in "Chapter Two," now circulating in a film version adapted by Simon from his orginal play and directed by Robert Moore, a frequent collaborator who has never threatened to impose a style of his own on the author's material.

"Chapter Two" is supposed to be an autobiographical romance, inspired by the events that united Simon and actress Marsha Mason in holy matrimony. Unfortunately, it remains wedded to comedy formulas as trite and superficial as those exploited in "The Last Married Couple in America."

Ultimately, there's little to choose between the two films. (The presence of Valerie Harper in interchangeable supporting roles also makes it possible to confuse them.) Simon's failure to distill the experience of bereavement and reawakened love in authentic words and actions dooms "Chapter Two" to marital-comedy cliche and a predictably complacent success.

Simon's style tends to trivialize experience through the tyranny of the punchline. By the time he tries to break out into a more informal and heartfelt style of expression, he's unfit for sustained eloquence.

To play fair, let's start with a nifty. The hero, James Caan as a recently widowed novelist named George Schneider, has arranged a brief get-acquainted date at the apartment of the heroine, Mason as a recently divorced actress named Jennie MacLaine. He inquires about her ex-husband, a former pro football player.

"He was cut the beginning of his second year," Jennie says. "Bad hands, I think they call it. Couldn't hold on to the football."

George replies, "Well, some coaches are very demanding." Not bad on its own terms, and potentially endearing too.

A whirlwind courtship of half a dozen scenes later, George has invited Jennie up to his place. Unfortunately, by this time they're sounding so professionally cute that the author himself appears to apologize for the artificiality of the repartee.

Just inside the front door, George playfully asks, "Shall we start with the bedroom?" When Jennie says okay, he adds, "If we start with the bedroom, we may end with the bedroom."

Jennie says, "Endings are just beginnings backwards," prompting George to reply, "It's going to be one of those fortune cookie romances, heh?"

I'm afraid so, heh-heh.

George and Jennie tie the knot. And why not? They seem to speak the same artificial language. Nevertheless, it appears that George may be too haunted by memories of his beloved first wife to embrace the chance at happiness anew with the near-worshipful Jennie. Faced with this obstacle, the romance degenerates from mere fortune-cookie superficiality into perfunctory crisis and psychoanalytic platitiude.

Chipper Jennie affirms her love for despondent George, who scarcely seems worth the bother, in a prolonged oration. You pray that she'll break through his resistance, if only to put a merciful stop to all the circumlocutions and I'm-all-right-you're-all-right banalities Simon puts in her mouth. In the longest summation since Clarence Darrow, Jennie ought to end with the line, "Your Honor, the defense rests." She comes close:

"If you want me, then fight for me, because I'm fighting like hell for you. I think we're both worth it . . . I apologize for taking up so much of your valuable time. I am now through."

If only she were, and he were, and the author were. Both the smothering ardor and fleeting sarcasm are lost on George, who confesses, "I didn't hear half of what you said because I was so mesmerized by your conviction." (Don't you just love it when a busy playwright can find the time to praise his own stuff?) Arbitrarily stringing out the crisis, George insists on getting away for a while. "Maybe I can get unstuck in Los Angeles," he says. "I'll be at the Chateau Marmont Hotel." Potentially a hilarious scene, this, but it's evidently meant to be taken straight.

Jennie pleads, "George! Couldn't I go with you? I wouldn't bother you, I would just watch."

Trying to regain the old form, George says, "Then the people next door would want to watch and pretty soon we'd have a crowd."

Jennie nudges away. "If you don't call me, can I call you?"

Nudging the audience, George replies, "You know, we may have one of the most beautiful marriages that was ever in trouble."

On the contrary, what plods across the screen is such a freakishly implausible, uninspiring love match that it seems presumptuous to ask, "Can this marriage be saved?" Maybe, but you're not persuaded it should be.

Mason wears out her welcome struggling to make something emotionally devastating out of a character defined by niceness. She doesn't have to work overtime to convince us that Jennie is undeniably a sweet kid, but her labors seem to have brought a professional reward: Mason's third Academy Award nomination.

Caan, far from appearing haunted by recollections of his first wife -- the key to sentimental authenticity here -- makes George look merely stolid and inexpressive. It sounds like a heartbreaking comment on her first marriage when Jennie rejoices in self-pitying George and vows to hang on despite his insensitivity because "I know a good thing when I've got it." It's a good thing that never meets the eye.

As I recall, Simon and Mason got acquainted during rehearsals for one of his plays. The idea of a love affair blossoming in that situation seems far more promising for movie purposes. As it is, "Chapter Two" doesn't get the sort of "opening up" it needs to become as flexible as the scripts Simon wrote directly for the screen, like "The Goodbye Girl" and "The Cheap Detective." Simon adds facetious touches that don't so much fill out the courtship as expose his philistine tendencies: George can't eat a spicy dish when he and Jennie go out to a restaurant or stay awake when they attend a concert.

At the same time, Caan's dull performance snuffs out the possibility of romantic tension or rapport. Perhaps Caan was excessively influenced by the original George -- Judd Hirsch, an actor of such distinctive gloominess that he may have succeeded in embodying the sort of sorrow that is meant to inhibit the character.

Speaking or sorrow, couldn't someone talk Valerie Harper out of her frightening new emaciated look? In "Chapter Two" she and Joe Bologna have custody of the subplot, a moralistic skit about unhappy adultery between the heroine's best friend and the hero's brother. Scanty costuming makes Harper's starkly muscled skeleton more dreadfully exposed than it was in "Married Couple," in which she also served as a feckless adulterer.

Slip the kid a monster sundae before it's too late! Harper's physique has become as grotesquely streamlined as Simon's worst quips.