CRUSING -- AMC Academy, Andrews Manor, Beacon Mall, Embassy Circle, Fairfax Circle, K-B Cerberus, Landover, Wheaton Plaza, White Flint.

"Cruising" is billed as a murder mystery -- the story of an undercover policeman who infiltrates New York's gay world to catch a psychotic murderer, or as a Daily News headline screams early in the movie, a HOMO KILLER ON THE PROWL.

As it turns out that headline sets the tone perfectly. "Crusing" is about undercover police work the way Playboy is about interviews. Directed by William Friedkin of "Exorcist" fame, the film is made up almost exclusively of lurid, brutal scenes designed to titilate and shock.

The movie has understandably come under fire from gay groups, and it bears two disclaimers. A written prologue tells us that it is "not intended as an indictment of the homosexual world." And midway through the movie, a weary, seen-it-all police captain tells the young undercover cop that the murder victims "were not in the mainstream of gay life. They were into heavy leather. S&M -- it's a world unto itself," he continues earnestly. That should take care of that little problem, you can imagine the filmmakers saying amidst pats on the back.

Unfortunately those two statements aren't enough to counter the effect of nearly two hours of assorted grotesqueries. Al Pacino, looking like a dazed Frankie Valli, does his best to add some humanity to the movie in his role as the young policeman, but between the script and direction it's a hopeless task. tThe film opens with a graphic knifing scene and goes downhill from there -- mutilated torsos, cruising in Central Park, peep shows, seedy hotel rooms, you name it. The camera lingers longest in the leather bars of New York's West Village.

The filmmakers tell us that the way of life they depict is typical of only a tiny segment of gay society. But there is an odly moralistic scene at the end of the movie, involving a "nice" gay man, which indicates that gay doesn't pay, period.

Technically the movie is flawless. One scene in Central Park, when Pacino confronts the murder suspect on a deserted rain-slicked path, is haunting and beautfully photographed. But that's hardly a reason to sit through the rest of this wretched film.