Taking a page from Hitchcock, "F/X" is a nicely knitted thriller, effective if conventional -- it's like watching an intricate arrangement of dominoes tumble. Which is a surprise, because it grabs you just as you're about to turn in your popcorn.

For the first 40 minutes, "F/X" jogs sluggishly in place, as we meet Rollie (Bryan Brown), a master of special effects (known in the trade, phonetically, as "f/x"). The government calls on him to stage the murder of a racketeer-turned-stool pigeon -- if the mob thinks he's dead, they won't try to kill him.

So we follow Rollie as he agonizes over his decision, makes love to his girlfriend (Diana Venora), says no, says yes, says let me think about it. The agonizing, the girlfriend and the crawling pace are supposed to make you care about the characters before the action starts. Which doesn't work, mostly because Brown, with his clipped Australian cadences and glittery blue eyes, is so tight-lipped and withdrawn an actor. It's here, too, that Bill Conti's gummy, phlegmatic score does the most damage. Conti's a genius of imprecision; faced with the discord between sound and image, you don't feel you're listening to a different movie -- you feel as though you're listening to five.

There's not much suspense here, either; when Mason Adams, as Col. Mason, growls, "You're 100 percent protected," you know it's time to duck. And soon enough, Rollie does the job, the government tries to do a job on him, and the movie takes off, not coincidentally because of the appearance of Brian Dennehy as a tough New York cop with a badge (and a heart) of gold. As in the rest of "F/X," there's no particular surprise here (the best cop on the force, doesn't play by the rules, blah blah blah), but Dennehy brings magic to the role -- he's large, and he enlarges it. With his sly eyes and little can opener of a nose, his shoulders a yard wide, his hair massing in gray curls behind his ears, he dances through the movie like a mastodon in toe shoes.

Dennehy's confidence is contagious. Director Robert Mandel flogs the pace, Conti's music gets . . . well, conventional, at least; and there's a spectacular chase choreographed by Gary ("Against All Odds") Davis. Throughout, the special effects (by John Stears, who did "Star Wars") are, appropriately, fine and often witty: Who hasn't wanted to see a restaurant flooded with lobsters when its fish tanks are riddled with bullets?

Screen writers Robert T. Megginson and Gregory Fleeman like their jokes (they've titled one of Rollie's legendary films "I Dismember Mama"); their use of props is fun, and they've filigreed the movie with enough twists and turns to keep you surprised. Some of those twists you might have seen before -- the basic setup, placing an innocent in the underworld, is standard Hitchcock, and the movie cribs from everything from "The Third Man" to "The Big Sleep." Then again, if you're going to rip things off, you might as well have good taste.

F/X, opening today at area theaters, is rated R and contains considerable violence, profanity and sexual situations.