IN FILM talk, F/X stands for special effects. And with the movie biz dominated by F/X wizards like Spielberg and Lucas, it was only a matter of time before the special effects got a movie of their own.

And so we get the gimmicky thriller "F/X," directed by Robert Mandel, with deceptions devised by Oscar winner John Stearns (Thunderball," "Star Wars"). As they should be in a movie that presumes to call itself "F/X," the illusions are all A-OK. It's the acting that's PU.

The intriguingly paranoid plot is similar to Brian De Palma's "Blow Out," which was about a soundman who finds himself witness to an assassination. In "F/X," Bryan Brown, coming on stern and silent like an Aussie Eastwood, plays Rollie Tyler, a leathery illusions expert who has done the awful honors for such movies as "I Dismember Mama" and "Vermin From Venus."

So realistic are Tyler's gory getups and movie massacres that he's called on by the Justice Department when it wants to stage a fake assassination in public. It seems a Manhattan mob chieftain is about to testify for the Feds, and they need to make it look like he's dead, for his own protection.

Tyler sets up a realistic restaurant shootout, but there's corruption afoot, and our double-crossed hero finds himself accused and on the run, working with real blood and brains.

"F/X" benefits from some (but not enough) behind-the-scenes glimpses of how life masks, blood blanks, explosions and other movie gimmicks are rigged. There is also a memorable careening car chase through a meatpacking district, and a very funny scene in which Tyler singlehandedly bags a mansionful of thugs with his bag of cinematic tricks.

Brown, looking stoic and resourceful, is good as Tyler, but the hammy performances by Brian Dennehy and Cliff De Young, and an unbelievable "dumb blonde" bit by Martha Gehman as Tyler's assistant, give the human part of "F/X" a first-take feel.

F/X (R) -- At area theaters.