IF YOU WANT to understand incest, wait for a re-run of Lolita. While Stanley Kubrick's masterpiece doesn't deal with technical incest, a sexual liason involving blood relatives, Lolita does capture that strange and tormented allure which a child can hold over an adult. The first, wonderful, utterly perverse shot of Lolita's toes contains more suppressed eroticism than all of Bernardo Bertolucci's Luna.

Judging from the grotesquely baroque poster and the huge press hype, however, Luna should shock and titillate its jaded audiences with graphic sex and perverted emotions. A film about incest should fascinate, challenge or perhaps disgust its viewers.

But bore them? Bertolucci commits the ultimate cinematic crime: his film is stultifying dull. Luna excites little besides yawns and the desire to leave the theater. By the time Jill Clayburgh has mouthed her last aria, most of the audience at the Sack Cheri were long gone. Approximately two hours, Luna seems an eternity spent in limbo. Hell, in the form of a truly low-grade bad movie would have been more exciting.

Bertolucci makes incest deadly by simply skirting the whole issue for most of the film. Caterina (Jill Clayburgh) is an American diva with an obnoxious, teen-aged son (Matthew Barry) and a pathetic, ancient husband who's efficiently knocked off in the opening sequence. Dad dead, it's off to sunny Italy for Caterina and Joey. The obligatory opening night sequence is filled with lots of American extras running about trying to look Italian by wildly gesticulating and screaming 'Brava, Brava.' Bertolucci also drags out an antiquated collection of cliches about opera and its fans. His women parade about a la Gertrude Stein and partake of lesbian love with decadent Italian countesses. His men lisp on about 'darlin' Caterina and swish about backstage. It would be funny if it weren't so offensive.

Joey of course, deserted by his famous mother, has taken to heroin and discovered the joys of sex with a pudgy little Italian girl. Mom finds out and for the next two hours Luna repeats a tiresome pattern of hit, scream, claw and shoot-up until the end mercifully arrives. The operatic finale in which all problems find their resolution through song makes the Sound of Music appear profound.

THE 'BIG' SCENE between Clayburgh and Barry is ludicrous; Mom pats junior's corduroys around the crotch area twice and bam, the earth moves. With a sensitivity level like that, how the hell does the kid ride the subway at rush hour? The other "big" scene has mom writhing about fully clothed, displaying to full advantage a mere pair of skinny legs. No sexual tension or even desire ever builds up between the two. The two moments of sexual activity occur for no apparent reason; Bertolucci never integrates this incest into the broader context of film. The only truly startling moment in the film occurs when Joey plunges a for into his arm. That's shocking. The single men who came with hats over their laps were sorely disappointed; Luna is not soft-core porn for the artsy set.

The acting fully matches the wooden level of the screenplay. Why did Jill Clayburgh ever attempt this part? As Erica Benton she was delightful. As a high-powered diva, she's positively grotesque. Those station-wagonned suburban looks don't help and that fabulously skinny body certainly doesn't look appropriate. Who has ever seen or heard an anorexic Joan Sutherland or Beverly Sills? Clayburgh careens about the screen, wildly overacting. Trying so damn hard, Clayburgh becomes positively painful to watch. Matthew Barry reveals some vestiges of talent but when delivering lines like "I must go; she awaits me", it's virtually impossible to appear anything but absurd.

AND ABOVE IT ALL, floats the moon. In Bertolucci's cosmos, there is neither night nor day, nor lunar cycles. Rather, there swims above us at all times, a huge flaccid orb, symbolizing-what? Bertolucci obviously doesn't know since this moon appears at any given moment, even in the early afternoon. This absurd use of the moon to symbolize essentially everything and nothing gives a hint of Luna's incoherency.