By making a big deal out of the fact that his supernatural chiller "The Mothman Prophecies" is based -- however loosely -- on true events, director Mark Pellington seem to be hoping the picture's vagueness and creative liberties might come under less scrutiny.

Furnishing the story about an epidemic of haunting phenomena in a West Virginia hamlet with an acutely icy and unsettling atmosphere, Pellington certainly makes it easy to go along for the ride. But whenever there's a break in the action, the film's fictionalized elements can't help but come into focus, requiring the viewer to beat back the same sense of curiosity required to get sucked into this creepy legend in the first place.

The "true events" on which the movie is based took place in Point Pleasant, W.Va, in the mid 1960s, where dozens of residents reported eerie encounters with a giant, shadowy, winged humanoid with glowing red eyes. Many more said they began hearing unearthly voices that vaguely prophesized impending disasters and other phenomenon.

These accounts (already the basis for at least one episode of "The X-Files") are mostly just alluded to in the film, which moves the action to present day and zeroes in on a star Washington Post reporter (Richard Gere) whose beautiful young wife (Debra Messing) dies after a car crash encounter with a (the?) mothman. Gere isn't sure what to believe when she cries on her deathbed, "You didn't see it, did you?" But two years later when his car breaks down inexplicably, he finds himself in Point Pleasant just in time for a rash of mothman sightings -- and investigating them soon becomes his obsession.

Gere's character is a Hollywood-retrofitted version of John Keel, an investigative reporter whose non-fiction book inspired the film. Of course, Keel doesn't have a dead wife and didn't experience sexual tension with the town's sheriff (Laura Linney) when he went there specifically because of the reports of supernatural encounters.

Even though I knew little about the story until reading up in advance of this review, it was a little too obvious where such fabricated accoutrements have been applied to this hero, and to the story in general.

"That's not coming from human vocal chords," declares a Generic Lab Coat Guy in a wholly supplementary scene, when Gere brings him a telephone recording of the mothman's voice, made during repeated, enigmatic and garbled calls to his hotel room. And let's not forget Gere's purely expository trip to visit a mythology expert (Alan Bates) whose own encounters with the Mothman turned him into a stressed-out paranoid.

The movie's seams may show, and it may be too deliberate and demonstrative in its cinematic suspense techniques -- enough already with the ambiguous point-of-view cam peeking at Gere through bushes, branches and fence posts! But Pellington gives "Mothman" an irresistibly uncanny ambience that goes a long way toward keeping the picture compelling, just as he did in the 1998 psychological terrorist thriller "Arlington Road."

By never clearly showing the mothman on screen, he avoids a slippery slope toward horror genre sensationalism. He remains centered on the characters, allowing Gere and Linney to flesh out the fear, stress and turmoil that threatens to engulf them as it did one of the locals (Will Patton, in an exhaustively agitated performance) when he couldn't stand the paranormal disquietude any longer. The director also has an eye for subtly jarring imagery. Even the town itself has a weather-beaten foreboding about it, with its faded storefronts and pavement as cracked as spring ice on thawing river.

Yet "Mothman" is so effectively atmospheric that even its minor contrivances become quite conspicuous as the film builds toward a catastrophic climax.

Like all movie characters who have frightful premonitions, the otherwise composed and reasonable Gere acts like such a nutcase when trying to warm people of impending doom that he is roundly ignored. Although it's treated as being pivotal to the plot, his intensifying closeness to the sheriff never feels entirely credible. Even incongruous background business seems to leap distractingly into the foreground at times. Couldn't Pellington come up with a better excuse for a minor character to be in the finale than to place her in a bridal shop, trying on wedding dresses at 6pm on Christmas eve?

Said finale is awash in such logistical fallacies, but like the movie as a whole, it's stimulating, startling and very well executed nonetheless.