STAGE REVIEW : Everything Is Relative in ‘David’s Mother’ : Bob Randall’s bittersweet work at the Pasadena Playhouse is no more than well-crafted sitcom about a well-intended mom and her retarded son.

PASADENA —  David, his mother Sally says, “is a piece o’ work.” He’s in his teens. He’s retarded. And she’s been known to refer to him as a moron.

If this sounds offensive, it is not offensive within the clearly defined confines of Bob Randall’s “David’s Mother,” which opened last weekend at the Pasadena Playhouse. The perimeters of the comedy are as secure as the walls of the modest New York apartment Sally shares with David.

Call that apartment a fortress. Call Randall’s play equally unassailable--a well-crafted comedy built around the familial havoc raised by the presence of a child as severely impaired as David. Sally’s defenses extend beyond merely bolting the door. Her way of shutting out reality and the world is to joke about it.

She’s been so protective of this son that she’s scared off her husband, Phillip, and her daughter Susan. But Sally doesn’t see it that way. “What am I supposed to do?” is her frequent refrain.

Is Susan a martyr or a monster? Neither. She’s the more ordinary victim of the baggage she brings to her situation. To hear her talk with her born-to-shop sister Bea, their mother was the real Godzilla who made Sally such an easy target for guilt and self-sacrifice. Psychology 101. Every relationship Sally has--with Bea, David, Phillip or Susan--is stewing in love-hate.

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When Bea insists that Sally come to brunch to meet John, a potential Prince Charming, watch Sally fight hard before surrendering--just as she later fights John.

Randall, who wrote “6 RMS Riv Vu” before becoming producer and head writer for TV’s “Kate & Allie,” knows how to press all the right emotional buttons. “David’s Mother” has humor and heart. What it lacks is depth. The blueprint for an emotional experience is in place, but the play behaves like Sally: It keeps the jokiness flowing but real catharsis at arm’s length.

In which case, you’ve got to hand it over to the cast. And director Josephine R. Abady does just that. The result in Pasadena is a production that is smart, superficial and only occasionally touching.

Ellen Greene, the deliciously wide-eyed stage-and-screen ingenue of “Little Shop of Horrors,” is an intelligent Sally whose pain, if fairly transparent, is seen more than it is felt--mostly because it is consistently buttoned up behind the snappy lines Randall has given her. This does not leave the play much room to dig.

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Norman Snow’s eloquent performance as John, Sally’s widowed suitor, lends that role greater depth and grace than one suspects it possesses. And as big-hearted sister Bea, the excellent Carol Locatell is restricted to a range of emotions that go from wistful affection to aphoristic cleverness. But she’s on a long emotional leash compared to the brief cameos allowed Jennifer Blanc as her teen-age daughter Justine, Peggy Blow’s compassionate case-worker Gladys, Vasili Bogazianos as David’s rational father or Leah Remini as his angry sister Susan.

In many ways, these are unfinished characters: sketches of people with the right impulses.

The one nonverbal contribution that speaks volumes is Karl Maschek’s as the David of the title. Maschek’s unerring absence of presence and his indulgence in the well-observed mannerisms and tics of the mentally impaired make him a remarkable foil for Greene’s anguish and ironic humor.

“David’s Mother,” however, is not Scott McPherson’s devastating “Marvin’s Room” or even Peter Nichols’ “A Day in the Death of Joe Egg.” Randall does not strike as savagely as all that.

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Things are too neatly laid out and too expediently wrapped up in an ending that offers us all but Sally and John riding off together into the sunset. Randall is not quite that blatant, but “David’s Mother,” which had the potential for something dark and stark as a valor-in-adversity comedy, chooses instead to play it resolutely safe.

The production design by David Potts (set), Marc B. Weiss (lighting) and Susan Denison Geller (costumes) is on target. But Steve Orich’s original movie-style music, with its upbeat rhythms and tinkling piano keys, serves chiefly to remind us that, for all its aspirations at something more serious, “David’s Mother” is just another feel-good comedy.

* “David’s Mother,” Pasadena Playhouse, 39 S. El Molino Ave., Pasadena. Tuesdays-Fridays, 8 p.m.; Saturdays, 5 and 9 p.m.; Sundays, 2 and 7 p.m. Ends Oct. 25. $31.50. (818) 356-PLAY. Running time: 2 hours, 15 minutes.