Even when his direction was shockingly effective -- in the smash hits "The French Connection" and "The Exorcist" -- William Friedkin always seemed a sensation-seeker rather than an artist.

So there may have been a dreadful inevitability about his attraction to the subject matter of "Cruising," a crime melodrama starring Al Pacino, looking profoundly depressed and miscast, as an undercover cop assigned to infiltrate New York's underworld of male homosexual bars and private sex clubs as part of the manhunt for a psychopath who stabs and mutilates homosexual victims. However, it appears as if this experiment in provocation may have blown up in the filmmaker's face.

The blowup began when the film was shooting on location in Greenwich Village last summer. Arthur Bell, a gay activist who writes for The Village Voice, spearheaded protests against the production, even urging harassment and sabotage to shut the company down.

Bell was quoted as saying, "I feel like the Godfather of the gay movement.

I put out a contract on Friedkin's movie, and I feel confident that it can be stopped. It it gets released, we'll hit the distributors."

His politics aside, one of the accusations in Bell's column has been verified with remarkable accuracy by the movie itself: "The script has no social value; everyone comes out looking bad -- cops, gays, even the city."

"Cruising" is a lurid, shambles, at once drawn to obscene stimulation in the form of hideous crimes and sadomasoschistic sexual appetites and yet dramatically evasive and incomprehensible. Even the most ardent sensation-seekers are likely to trudge out of this fiasco with their brows knit into a collective "Huh?"

Serving as his own screenwriter Fridkin seems to have gotten confused trying to stitch together remnants from sources that refused to interweave effectively: the nastily booby-trapped plot of Gerald Walker's original novel, published in 1970; the recollections of a former cop, Randy Jurgensen (cast in the film as a homicide detective, along with Sonny Grosso, the old veteran of the French Connection case), who once posed as a homosexual in the early '60s; several unsolved murders in the New York police files.

From Walker's novel Friedkin borrows a grotesque climactic twist implying that after the killer is apprehended, the undercover cop may assume this homophobic slasher's m.o. The book's internal evidence obliged you to believe the switch, although it appeared to happen inadvertently and made you want to chuck the book in disgust. While pretending to follow hunter and hunted along parallel tracks in alternate chapters, Walker had treated the cop with misleading sketchiness while devoting detailed study and analysis to the demented personality of the killer.

The internal evidence in the movie, which obscures everyone systematically, makes the idea of Pacino metamorphosing into a killer somewhere off-camera seem farfetched. Friedkin plants this abusrd suggestion anyway.The likelier possibility is that the cop and his girlfriend (the lovely Karen Allen in an unrewarding, perfunctory role) may grow fond of kinky sex as a result of his dangerous assignment. When last seen, Allen has tried on his heavy leather costume and Pacino waits expectantly as she jingle-jangle-jingles in his direction.

The most revealing title for the movie would be "Slumming," but are the homosexual dives Pacino investigates a picturesque attraction to many people, straight or gay? And to what dramatic or social purpose has Friedkin embarked on this unwelcome expedition? Given the special nature of the hero's imposture and the ultrasordidness of the milieu he's expected to infiltrate, "Cruising" would seem to demand extraordinarily lucid and discreet depiction. But Friedkin spreads chronic irrelevancy and hateful confusion from the outset.

For example, when Karen Allen informs Pacino, "Your father called today," and the music murmurs nervously over his could-mean-anything-or-nothing expression, how much should we make of it? Or when he says grimly, "There's a lot about me you don't know." If these were intended to foreshadow affinities with the psycho he's hunting or alert us to a sexual identity crisis destined to be illuminated in detail later, the follow-up material must have been mislaid.

Friedkin's line of reasoning is often brutally gratituitous or absurd. Did he imagine he had something significant in mind when he followed a scene of one stabbing with a scene of Pacino and Allen copulating? Master of irony, indeed! The message of this mad juxtaposition seems to be, "The girl can take it."

Is Joe Spinell's gay-baiting but evidently homosexual cop supposed to be a real character or some kind of rhetorical device? Why do the homicide boys go through an elaborate rigamorole entrapping and brutalizing a suspect whose guilt or innocence could be established immediately by finger-print evidence? Why does Paul Sorvino, cast as Pacino's superior, walk like Walter Brennan? Why should we accept the fictions that Pacino is in his late 20s and prepared to pass as a homosexual hustler?

Pascino doesn't look young enough or fit enough to succeed at this particular disguise. Moreover, he appears to regret accepting the job from the very beginning. Upon entering the teeming bars and catching the regulars in their customary erotic tableaux, Pacino looks as if he'd prefer to be anywhere but there. And who can blame him? That instant, sad-eyed alienation is the most convincing aspect of his performance.

"Cruising" accelerates the process of narrative disintegration apparent in Friedkin's recent flops: the pretentiously murky "Sorceror," a bundled remake of the great French thriller, "The Wages of Fear"; and the ponderously facetious "The Brink's Job," a mangling of one of the great real-life crime stories of recent times.

At "Cruising's" sole press screening in New York two weeks ago, even spectators inclined to give Friedkin the benefit of the doubt found the picture indefensibly vague. As for Friedkin himself, he was quoted as saying, "My responsibility is to tell the story the way I see it."

There's the rub: Judging from the finished film, he never had a coherent vision of the story, the characters or his own motives.