LIVIN' FAT, a play by Judi Ann Mason. Dlrected and designed by Robert Edward West.

With Maxine Davis, K. Halima-Shalom, Fred Harris, Mel Ville Mathews, Carol Marie Perry, Michael Murphy, Jovan More and Keith Fulwood.

At the Environmental Theater, 916 G St. NW, at 7:30 tonlght through Sunday night, and Sunday afternoon at 3.

Take my word for it that the ending of "Livin' Fat" is, by all the accepted standards of prime-time television morality, positively depraved.

That's just about the only feature of this raucous production that would not sit comfortably in an episode of "Good Times," the TV series which regularly employs the playwright, Judi Ann Mason.

"Livin' Fat," at the University of the District of Columbia's Environmental Theater, was an extracurricular activity for Mason, who is 23 and black and writes scenes with shotgun pace. But she has pumped her play full of elements that are pure -- including for instance yet another rambunctious, irreverent grandmother. Her favorite magazine is "Playgirl," generally read sideways and, if her Bible-quoting daughter is on the premises, concealed inside a copy of Ebony.)

The basic situation, plus or minus a plot twist or two, would certainly not shock anybody in the Norman Lear hierarchy.

A family suddenly comes into money -- bad money. The son works as a janitor in a bank, the bank is robbed, and when ordered to the floor he falls fortuitously onto $15,000 dropped by one of the robbers. His family, when they discover his wealth -- and its source -- has misgivings. What to do?

Most of "Livin' Fat's" dialogue, too, would pass muster with the Cbs/ censor. And Mason has delivered the usual quota of barbed intra-family putdowns.

"I raised my son to do good according to God," says the distraught mother. "I taught him the ways right."

"Honey, hush up!" counters the irreverent grandmother "You sound like Reverend Ike."

But Mason shows, in gentle flashes, a subtlety in her technique and an anger in her purpose that make her desire to write plays more understandable.

"You know, we shoulda had more children," laments the father. "That way they wouldn't take out so much for taxes."

The ending is, well, out of O. Henry by way of Jerry Rubin.

The UDC performers, a peppery lot themselves, have infused the show with appropriately manic fervor. Keith Fulwood, as the grossly behaved neighbor, has a voice and physique of Zero Mostel proportions, and an infectious feel for farce. And Michael Murphy, who is alternating the role of the son with Jovan More, makes perplexity funny after the fashion of Richard Pryor (although perhaps he has studied Pryor a bit too closely for everyone's comfort).