M. Night Shyamalan's "Signs" is a science-fiction movie with a minimum of special effects and a maximum of quiet, slow-building tension. It's not a "space opera" so much as a piece of space chamber music. Exceptionally well-crafted and often stunning visually, it's an unusual vehicle for star Mel Gibson. This is an angst-ridden drama that keeps the invading aliens way in the background, set in landscapes that remind you of Andrew Wyeth paintings: impeccable, vast, shivery views of the Pennsylvania farmland.

It's also a movie that didn't make much sense to me, not because it dealt with invaders from outer space and the mysterious signs they leave, but because the main humans in the story acted with such self-destructive strangeness. That doesn't really ruin the movie. Science-fiction thrillers don't depend on psychological veracity or depth, and "Signs" mostly succeeds in compelling attention and periodically making the audience jump. It's a film of gathering darkness and dread, pitched in ominous minor keys. But from the moment the "signs" begin appearing - huge symbolic crop circles and arcane symbols hewn out of a Pennsylvania cornfield in the dead of night - the adult humans begin acting moonstruck and daft.

Shyamalan, best known for "The Sixth Sense," is a writer-director who deals with supernatural or science-fictional subjects by treating them as if they were real. But the characters here - led by Gibson as Graham Hess, a tormented ex-preacher - don't always act like real people faced with actual peril. Instead, Graham and his family - younger brother and former minor league baseball player Merrill (Joaquin Phoenix) and tots Morgan (Rory Culkin) and Bo (Abigail Breslin) - keep putting themselves in awful predicaments with little discernible reason. At times, it's as if we were watching the heroine in some old cliff-hanger serial running from one sawmill to the next, waiting for the villain to show up. (Luckily, he does.)

Graham, who keeps correcting everyone who calls him "Father," lost his faith after his wife died in a grisly road accident caused by neighbor Ray Reddy (Shyamalan himself). Now he has to confront extraterrestrial horrors on his lonely Pennsylvania farm. The adults are trapped in grief and disillusionment, but the kids, like the ones in Shyamalan's previous thrillers, are better adjusted to life's chaos. They see where the adults don't. In a way, the movie almost seems to equate religious faith with a belief in extraterrestrials. But the aliens here are no gentle E.T.s; they're more like the fiends in "Independence Day."

"Signs" takes some of its visual cues from Alfred Hitchcock's "The Birds" and George Romero's 1968 zombie-attack B-movie classic "Night of the Living Dead." Unlike those movies, there's a big flaw in this script: no sensible explanation of why - unlike the rest of the world, where cable news is churning out shots of crop circles and invading forces everywhere - hardly anybody in Bucks County or beyond checks out Graham's farm except for one local policewoman, Caroline Paski (Cherry Jones). CNN, the newspapers the police and government all neglect or ignore the place, leaving the family in a limbo - as if the humans had become zombies even before the living dead got to them.

For a movie that's about a crisis of faith, "Signs" often suffers breakdowns in logic. I couldn't figure out why Graham didn't stock up on weapons, or call the police or Army - or why, when it seemed obviously time to flee, he held a family vote and let himself be bound by a tally including two young children. We're probably meant to suspect that a religious temperament keeps him in this pacifist state - except that this is a man supposedly fleeing from God. Toward the end, when Shyamalan gives us a dramatic two-shot tableau of Graham reciting a monologue to his child while someone or something tries to break down the door, I decided they all must be in somebody's nightmare. But though I guessed the ending of "The Sixth Sense" halfway through, I was wrong here.

On a technical/performance level, "Signs" is exemplary. The film boasts dry humor and jarring shocks, plus moments of breathtaking mystery. But Shyamalan may be mistaken in letting himself be typecast as the New Hitchcock, master of the New Suspense. He's good at suspense scenes, but his first two films, "Praying With Anger" and "Wide Awake," weren't thrillers at all, but a drama and a comedy about quests for self-knowledge - and they had qualities he's left mostly untapped since.

Just as "Unbreakable" seemed feebler in conception than "Sixth Sense," "Signs" - though his most visually beautiful work - seems thinner than either, barely more than a sketch for a movie, with characters trapped in formulas. Beautifully trapped perhaps - but paralyzed nonetheless.

3 stars (out of 4)
"Signs"

Directed and written by M. Night Shyamalan; photographed by Tak Fujimoto; edited by Barabra Tulliver; production designed by Larry Fulton; music by James Newton Howard; special effects by Industrial Light & Magic; produced by Kathleen Kennedy, Frank Marshall, Sam Mercer, Shyamalan. A Touchstone Pictures release; opens Friday, Aug. 2. Running time: 2:00. MPAA rating: PG-13 (some frightening moments).
Father Graham Hess - Mel Gibson
Merrill Hess - Joaquin Phoenix
Morgan Hess - Rory Culkin
Bo Hess - Abigail Breslin
Officer Caroline Paski - Cherry Jones Ray Reddy - M. Night Shyamalan

Michael Wilmington is the Chicago Tribune Movie Critic.