GIBSON'S STRETCH INTO PARANOIA.

Byline: Amy Dawes Daily News Film Critic

Mel Gibson seems to have a thing for playing noble but disadvantaged outsiders; witness his directing debut, ``The Man Without a Face,'' in which he played a scarred and mistrusted teacher who became the savior of a boy.

In that movie, it was a stretch to imagine the hunky Gibson, with his chiseled features and sparkling blue eyes, as a guy whose looks could scare people away; in his new movie, ``Conspiracy Theory,'' it's equally a stretch to imagine him as a disheveled New York cab driver suffering from rampant paranoia - one of those nutty, nattering guys on the street whose ramblings prompt other people to rush off in the opposite direction.

Perhaps that's what drew Gibson to the role: the acting challenge, along with his reputed real-life fondness for conspiracy theories. He does a creditable job navigating the tricky distance between seeming really disturbed and seeming reachable. Even so, he's too much the movie star to really disappear into the part; if anything, it's his patented charisma that gives this creepy potboiler some commercial appeal, and that makes its unlikely love story - between him and Julia Roberts - remotely convincing.

``Conspiracy Theory'' reunites the ``Lethal Weapon'' team of Gibson, director Richard Donner and producer Joel Silver in a suspense story that's buoyed somewhat by a playful sense of humor but bogged down by a plot that develops too long and too late.

Gibson is kind of a crackpot in the ``Lethal Weapon'' series, but here he's got a lot more fractures as Jerry Fletcher, a down-and-outer who manages to make a living as a cabdriver even though his overworked mind is crackling with paranoid theories about the oddball events he witnesses on the streets and in the media.

Every so often, he barges into the offices of a pretty, red-tressed federal prosecutor, Alice (Julia Roberts). In a desperate bid for attention, and because Jerry once saved her from muggers, she indulges him - to a degree.

Alice is particularly susceptible to his theories because she herself lives an isolated life, obsessed as she is with the truth behind the recent murder of her father, a federal judge.

But one day Jerry turns up at the courthouse blubbering and wounded, and it's clear that he's not just crazy when he says that bad people are after him.

The conceit of the movie, penned by Brian Helgeland, is that Jerry - one of those nuts who imagines black helicopters trailing him and nefarious government plots - really IS the victim of an outlandish conspiracy involving just such elements.

Movie-reviewing protocol, thankfully, prohibits a retelling of the far-fetched plot details. Suffice it to say that there's a lot more linking Jerry and Alice than meets the eye. Their relationship - which survives even her discovery that he lives in a bunker, padlocks his refrigerator and publishes a newsletter with a subscriber base of five - is intriguing enough to distract most people from the plot flaws. But even that doesn't make the movie particularly worthwhile or excuse its tacked-on, unnecessarily upbeat ending.

THE FACTS

The film: ``Conspiracy Theory'' (R; violence).

The stars: Mel Gibson, Julia Roberts, Patrick Stewart.

Behind the scenes: Directed by Richard Donner. Screenplay by Brian Helgeland. Produced by Joel Silver. Released by Warner Bros.

Running time: Two hours, 15 minutes.

Playing: Citywide.

Our rating: Two and One Half Stars.

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Photo

Photo: Mel Gibson is a paranoid taxi driver who gets involved with Julia Roberts' isolated federal prosecutor in ``Conspiracy Theory.''