A 12-year-old Prince William County boy was arrested late yesterday after he allegedly shot and wounded his mother and three other members of his family with a 22-caliber rifle at their rural Nokesville home about 35 miles from Washington, county police said.

The boy's mother, Frances Mandley, 42, was in critical condition last night at Washington Hospital Center. Officials said she had been shot in the chest and stomach. Jo Ann Swain, 25, a sister of the boy, was listed in fair condition at the hospital with a gun-shot wound to her neck. Both had been brought to the hospital by helicopter.

Another sister, Bonnie Hemmingway, 23, and her 14-month-old daughter, Kelly, were listed in stable condition at Prince William Hospital in Manassas. Hemmingway had been shot in the neck and chest. The baby underwent surgery for a gunshot wound to her stomach.

County police said late last night that they had not establised a motive in the shootings, which occurred about 5 p.m.

Police responding to a call about the shootings said they found the 12-year-old standing in the front yard of one of two adjacent homes occupied by the family. The four victims had been shot while in a bedroom of one of the homes, police said.

Prince William police Sgt. Charles Deane said the boy was not injured. He was taken to the Northern Virginia Detention Center in Alexandria and was charged with four counts of felonious assault.

The boy's father, James E. Mandley, 43, an employe of Randy's Frozen Food Inc., of Manassas, said his son had never been in trouble with police.

"They called me at work and told me to come home fast," Mandley said. "There was a whole bunch of cars in front of the house and they grabbed and brought me to the hospital."

Mandley said his son is a seventhgrader at Nokesville Junior High School. The family lives at 12705 Hazelwood Dr. in a sparsely populated area of the county southwest of Manassas.