MISS UNDINE'S LIVING ROOM By James Wilcox Harper & Row. 275 pp. $16.95

JAMES WILCOX'S third novel, Miss Undine's Living Room, may lack grandeur and subtlety, but readers are in for a lot of recklessly clever fun. Inviting this chockful book into your head is like engaging a circus to perform in your very own living room. Too much, but wow! The novel is by turns hilarious, silly, tacky, tender, maddeningly digressive, and as brimming with off-the-wall canniness as any modern comedy of manners I know. Miss Undine's Living Room feels as if it were peopled by a cast of thousands -- mostly twangy loudmouths, all holding forth on assorted dissatisfactions and dilemmas, all living in dumpy Tula Springs, Louisiana, where the choice one has is between "being completely ruined or dying of boredom."

Of course the principal characters of this novel are far too meddlesome to die of boredom. Even now their voices linger on, brash and yammering. At times I caught myself reading with my fingers in my ears!

Meet Olive Mackie, a secretary at City Hall who works in Dead Records. The novel opens with her changing her octogenarian uncle's diaper. An enfeebled mnemonist, Uncle L.D. is Olive's bane, his maintenance topping the list of dead-end chores that have dwindled her spirit. Olive is married to Duane, everybody's high school dreamboat gone-to-seed. Duane lost his job in real estate and now sells cheese logs. Olive's teenaged son, Felix, enrolled at the local Christian academy, has reformed from his punk, petty-thief days and now pals self-righteously around with Mormons.

Some of the book's most wacky and inspired dialogue flashes between mother and son. Here, having discovered her discreet cache of marijuana, unctuous Felix admonishes Olive: " 'Every puff means you're casting your vote for child pornography, gun running, heroin addiction, armed robbery, murder, wife beating, child abuse.' He was perfectly calm while reciting his list. 'Enjoy.' " Olive, listening to yet another of his harangues, replies, "Honey, why don't you go read Leviticus or something."

As if Olive's life isn't complicated enough, she falls in lust with Dr. Bates, a mild-mannered, befuddled dental student who "greatly feared being the source of any pain or discomfort for a fellow human being." Dr. Bates lives with his ex-mother-in-law, feisty Mrs. Undine, a retired but relentless school teacher who once taught Olive home ec (back then the kids called her "Old Lady Undies"). In her spare time Mrs. Undine volunteers to assist shut-ins with exercise therapy, which is how -- over Uncle L.D.'s prone, decrepit body -- she and Olive are reunited. Eventually the two are thoroughly enmeshed in a series of events riddled with social, political and sexual intrigue.

MRS. UNDINE'S living room, like the drawing rooms of satirical comedy, offers a forum for all sorts of shenanigans that range from bickering to flirtation to full-fledged sex. It's an Oscar Wilde-meets-Tammy Faye Bakker kind of place.

James Wilcox is a whiz at swift, zingy character sketches that both summarize and dismiss. Mr. Versey, Uncle L.D.'s despicable nurse, is described as "a former Grand Exalted Something-or-other of the Ku Klux Klan" who "used to work in the post office until he learned he was allergic to the padding in jiffy bags." The Mayor of Tula Springs "was handsome in the bland, neutered style of a soap-opera patriarch and sweated profusely as if he were under a klieg light." Characters abound with names like Dewey Fitts and Nesta Versey, and there is a creationist-liberal high school principal who shaves under his arms.

But then what? Even the book's leading lady, Olive Mackie, suffers from a superficiality that is barely disguised by the author's obvious affection for her. If Olive really changes in the book, it's because Wilcox insists upon it, well, because somebody's got to. But mostly Olive seems afflicted by the same arrested development that debilitates other, lesser characters and which reduces their impact to that of amusing, well-drawn cartoons.

Uncle L.D. is perhaps the exception. His victimization by practically everyone arouses genuine sympathy and outrage. The crimes committed against him are mostly ignored while he is accused of murder. Did he or didn't he shove creepy Mr. Versey out the window? One finally begins to ask: who cares? Mr. Versey, totally loathsome, is wholly expendable.

One indulges the antics of such characters only to discover, after many pages, that they end up being exactly the way they were to begin with: quirky specimens of the human race, tedious oddballs specializing in absurdity but strangely palatable because Wilcox never takes them very seriously himself. He is never overly earnest about their foibles and mistakes.

James Wilcox certainly comprehends the worst about people, but he delights mischievously -- never cynically -- in his knowledge. What he knows he passes on with the compulsive congeniality of a joker. You have to admire an author who can depict the narrowest of hearts and minds with such largesse.

Marianne Gingher is the author of the novel, "Bobby Rex's Greatest Hit."