As a rule bad manners make good, or at least diverting, theater. The Australian film "Don's Party," now at the Outer Circle and K-B Janus, is certainly no exception.

Set on Oct. 25, 1969, a national election day in Australia, it depicts a rowdy, unraveling evening of indiscreet conversation, boozing, leching, dining, skinny-dipping and backbiting shared in unequal portions by five more or less mismatched, incorrigible couples and one stray male gathered at a suburban rambler in Sydney for the ostensible purpose of watching the returns on television.

Derived from a hit 1971 play by David Williamson, this movie version appeared five years later and duplicated the success. Bruce Beresford directed from an adaptation by Williamson himself, transposing the action to the authentically cramped quarters of a smallish suburban haven, photographed with exceptional dexterity and ingenuity by Don McAlpine.

A peculiarly appropriate, jaundiced selection for an election season in which liberals may be blissfully deceiving themselves all over again, "Don's Party" suffers no apparent loss of humorous pertinence or authenticity because of the time lag. Certain kinds of vulgar, insulting social intercourse are probably funny regardless of the historical setting, but Williamson gets extra mileage out of the comedy of compulsive, drunken misbehavior by accurately recalling the distinctively absurd, desperate cant that typified aspiring and largely frustrated middle-class hedonists who let themselves be seduced and betrayed by the great Permissive Hoax of the '60s. The most swinish and self-righteous inebriated husband at the party, a psychologist named Mal (Ray Barrett), is moved to the following grandiose complaint after an evening riddled with sexual rebuffs: "Everybody talks immoral, but when it comes to the crunch . . . The whole of Western civilization smacks of hypocrisy!"

One gathers that Australian political and class attitudes parallel familiar American patterns. The host, Don Henderson (John Hargreaves), is a university English teacher of failed literary ambitions and shaky domestic authority but enduring self-indulgent smugness. Anticipating a Labor Party victory, he ostentatiously brushes aside Liberal Party literature outside the polling booth and proclaims "We're celebrating the end of 20 years of conservative rule!" before the guests arrive, prompting his disaffected wife Kath (Jeanie Drynan) to retort, "It's just an excuse for a booze-up." She's right.

The amusing but oddly assorted partygoers include three married couples in addition to Don and Kath: Mal and his cynical, headachy wife Jenny (Pat Bishop), whose association with the Hendersons evidently harks back to college days; Simon (Graeme Blundell) and Jody (Veronica Lang), naive and pleasant but politically conservative suburbanites who find the going a little treacherous upon entering a circle dominated by opinionated, contemptuous left-wingers; and Kerry (Candy Raymond), a middle-class bohemian artist, and her glowering, creepily solicitous mate Evan (Kit Taylor), supposedly a dentist but easier to accept as a sociopath.

A brash ladykiller named Cooley (Harold Hopkins) shows up with a wanton playmate named Susan (Clare Binney), who whispers "I'm gonna s---- you later on" when introduced to her host. Mack (Graham Kennedy), the stag, is an amiable, beefy-faced, self-confessed degenerate who announces that he and the missis, Ruth, have separated; however, she's present in a sense, because Mack has brought a large glossy of Ruth posing provocatively in the nude. "I'm a bit off about sex," he explains later when reflecting on the overdeveloped nature of his voyeuristic streak.

While Susan puts the make on Don, Cooley lures Kerry into the back bedroom and Mack begins to ingratiate himself with Jody. Mal gets shot down immediately when approaching all three targets. On the sidelines Kath and Jenny cultivate their slow burns and eventually express their unhappiness in speeches which suggest that their marriages are unlikely to last out the '70s.

The mild-mannered, apologetic Simon, portrayed by Blundell as a miniaturized, wimpier image of Hugh Hefner, right down to the pipe, is forced to go home alone when it becomes clear that his wife is in the mood for a fling. Summoning up as much dignity as possible while missing a button on his safari jacket, Simon exits with this ringing denunciation: "I didn't realize that university-educated people could be so bloody uncouth!"

The shortcomings in Williamson's bawdy, witty and fitfully penetrating text are as obvious as its enjoyable theatricality. The material remains superficial and inconclusive. "Don's Party" leaves it unclear whether the writer and director prefer to take the characters lightly or profoundly. The scenes impose themselves in gratuitously funny fits and starts, and the actors are consistently vivid company, but the play doesn't seem to deepen or accumulate a coherent dramatic outlook as the party wallows along.

I suppose the filmmakers might be faulted for shooting fish in a barrel, but I never got the impression that they felt vastly superior to the group of characters they exploit for satirical play. "That's like any Australian party I've ever been to," Beresford remarked matter-of-factly when confronted by foreign reviews that jumped to scandalous conclusions.

"Don's Party" owes a good measure of its comic gusto and accuracy to the impression that the filmmakers not only know these supposedly enlightened brutes but get a considerable kick out of their uncouth impulses.