Signs is three-fourths of a terrific movie. For most of its footage, the new thriller proves that director M. Night Shyamalan can weave an eerie spell and that Mel Gibson can gasp, shudder and even tremble without losing his machismo. And then comes the final quarter. The director`s latest two films, The Sixth Sense and the less successful Unbreakable, made his name synonymous with twistendings. But the warm-hearted Signs leads to a simplistic finale, constantly foreshadowed throughout the movie. Moviegoers will discuss the conclusion, as they did with The Sixth Sense, but Signs will polarize its audience into fervent pro or con camps.

Yet there is much that should make audiences cheer. Mr. Shyamalan knows what scares us. As a result, Signs is simultaneously the year`s scariest and most restrained movie. Without reveling in the slime and goo that symbolize most cinematic aliens of the last 20 years, Mr. Shyamalan brings the mysteries of aliens and crop circles to startlingly intimate terms. Most of the action occurs in and around a Pennsylvania farmhouse, and never before have cornstalks looked so ominous. The farmhouse interiors are even scarier. When the family hides in the basement, you wonder what deviltry awaits upstairs. When in the family room, you shiver at what might lie beneath. As in Poltergeist, the television set is far from a reassuring staple.

As the family patriarch, Mr. Gibson gets his customary 139 close-ups. But this time he earns them. Rarely has he looked worse or acted better. The lines in his face are completely credible for his role of grieving widower Graham Hess, a former clergyman who gave up the cloth six months ago when his wife died in a car accident. Mr. Gibson has never been more forceful than when venting his wrath at God and when finally allowing his stoicism to shatter. The former Father Hess now lives in Pennsylvania`s Bucks County, tending the farm with his two appealing young children and his well-meaning brother. Even before crop circles encroach the farmland and aliens threaten to invade, each family member must combat private demons.

The children try to maintain high spirits, but 10-year-old Morgan (Rory Culkin) and 5-year-old Bo (Abigail Breslin) naturally mourn the loss of their mother and sense their father`s emotional distance. Graham`s brother, Merrill (Joaquin Phoenix), is tormented by his brother`s tragedy as well as his own failure to achieve stardom as a baseball player.

All the performances are superb. Mr. Phoenix, a fast replacement for an ailing Mark Ruffalo (You Can Count on Me), is altogether winning as he combines a definite jock attitude with a warm heart. Ms. Breslin is adorable and gives only mild hints that she knows it. Mr. Culkin, of the well-known acting tribe, is strong and vital. His asthma is a key plot element, although memories of Jodie Foster`s diabetic daughter in The Panic Room dilute its impact. Lauded stage actress Cherry Jones gives another warm and empathetic performance as the town sheriff. Mr. Shyamalan himself appears briefly as a veterinarian. Like his film, he is both frightening and restrained.

Signs probably will be more heavily appreciated in retrospect when its ending is accepted on its own terms. For now, Mr. Shyamalan is a victim of expectations created by The Sixth Sense. But as that 1999 film proved, his movies can be seen more than once.