"Be yourself! Be charming, be debonair!" urges Alan King, a naturally gregarious theatrical producer, in conversation with Al Pacino, a naturally morose playwright, prior to dinner with two potential backers. Looking at Pacino, you think King has to be kidding.

Eager to seem warmhearted and endearing, "Author! Author!" is frustrated by Pacino's conspicuous resistance. If anything, this uncharacteristic vehicle illustrates his inability to lighten up an emphatically gloomy, brooding screen presence. King's admonition comes early in the story, a rather faint, apologetic variation by playwright Israel Horovitz on sentimental comic themes exploited more effectively by Neil Simon in "The Goodbye Girl" and Robert Benton in "Kramer vs. Kramer."

In addition to the cheerless personality, Pacino's maddening articulation would seem to argue against further flings at comedy. Line after line is obscured by his whispery mumble, and this mangled speech seems particularly inappropriate in a character who's supposed to be a playwright.

Pacino first made a name for himself playing a menacing punk in Horovitz's off-Broadway play "The Indian Wants the Bronx." This reunion suggests that actor and playwright must have kicked themselves for missing a golden opportunity when "Kramer vs. Kramer" came out. While struggling through the rehearsals of a new play, hero Ivan Travalian must also cope with domestic betrayal and crisis. His second wife Gloria (Tuesday Weld) admits she's having an affair and then flies the coop, leaving Ivan to look after a quintet of children--his own son Igor (Eric Gurry, a deft, big-nosed teen-ager whose comic finesse calls embarrassing attention to Pacino's acting defects) from a previous marriage plus two younger stepsons, Spike and Geraldo (B.J. Barrie and Benjamin H. Carlin) and stepdaughters, Bonnie and Debbie (Elva Leff and Ari Meyers), the spawn of his second wife's three previous marriages.

The basic ingredients seem reliably appealing. On the professional front Ivan is entangled with the play and then a blossoming affair with the leading lady, played by Dyan Cannon. On the home front he's preoccupied with compensating for Gloria's defection and maintaining a stable domicile. Gloria's pattern, we're informed, is to tire of her mates, take off and then reassemble her brood upon remarrying. Initially, Spike and the girls agree to rejoin their natural fathers, but they soon return, determined to stay with Ivan, who pretty much Has It All at the fadeout--a hit play, custody of five happy and adoring kids and the satisfaction of having rebuked his unfaithful wife in public. The affair with the leading lady seems to be on hold, but then it's already been peculiarly disillusioning to see that not even an actress as lively and amusing as Dyan Cannon can break through Pacino's moody defenses.

The case for Ivan's paternal virtue seems so synthetic that it's especially embarrassing to throw Pacino a speech in which he tells off Tuesday Weld, smiting her with wet-noodle epithets like "uncaring" and "unfeeling." In this case the cop-out wife is identified as a deplorable sort of Goodbye Girl, and her rationalizations are designed to confirm accusations made by her kids rather than defend herself: "Sooner or later I'm leaving, because that's what I am. That's what I do . . . I get married a lot. I have a lot of kids . . . I am what I am." How did that echo of Popeye creep into her speech?

The kids are the most appealing element in the movie, and the most interesting undeveloped theme is the nature of sibling companionship and conflict between a set of kids thrown together as a result of their parents' marital vicissitudes. Preoccupied with contriving sympathy for the dismal Pacino, the writer and director (Arthur Hiller, who's never better than the material he's given) fail to devote sufficient footage to the society the children share among themselves. With the exception of Gurry's Igor, the strongest characterization in the script, and Carlin's little Geraldo, who's thrown an excess of adorable business, the kids' roles seem skimped and tentative. This group doesn't begin to get you where you live, but it provides "Author! Author!" with its only trace of genuine human interest.