A 12-year-old boy plotting to frighten or even kill students who had teased him and then hold hostages to extort money was arrested yesterday morning at a Prince William County middle school after an administrator found him with a loaded rifle and two other guns, police said.

The seventh-grader was arrested in full camouflage gear on the last day of school after officials at Bull Run Middle School locked down the building and police stormed it under a plan developed after the shootings at Colorado's Columbine High School in 1999.

Police also arrested the boy's mother, Naomi Lewis, 38, a cafeteria worker at the school in the county's Gainesville section, and charged her with possession of a weapon on school property, law enforcement sources said. The boy had gotten a ride to school with his mother and left the guns in her car. Lewis noticed the guns and locked the car but never reported that they were there, police said in a statement. The boy later went back with a car key and retrieved the guns, police said.

Lewis did not know her son had a key and did not know of the plot, sources said. The guns belonged to the family, and neighbors said police removed about 20 additional weapons from the home on Brave Court in Haymarket.

Police Chief Charlie T. Deane said detectives believe that the boy wanted to scare or hurt other students and that he also was planning to take hostages.

"Some information leads us to believe there could have been a hostage situation with demands for money," Deane said. "It's still early, and we just don't know the extent of it yet."

Detectives were questioning about 10 students who learned of the student's plan in recent days but either did not take him seriously or did not believe he would go through with it. Deane said police are also investigating whether some students had agreed to take part in the plan and whether others "were going to do it and then changed their mind."

No shots were fired, and the student never pointed a gun at anyone during his apprehension, police said. It is unclear whether the student pointed the gun before police arrived. When he was arrested, he was talking to a school administrator and carrying a loaded .30-06 rifle. Police also found a .410-gauge shotgun and a .22-caliber rifle in a bathroom, where the boy was initially spotted.

As police charged the school, the 1,100 students inside the two-year-old building were locked in their darkened classrooms. After police went room to room searching for weapons, the students were taken to nearby Tyler Elementary School, where shaken parents arrived throughout the late morning and early afternoon to pick them up.

"You hear all this stuff, and you never think it'll be you," said Jane Buchanan, mother of a seventh-grader.

Her son Taylor Buchanan, 13, said: "I thought that we would sign yearbooks and say goodbye and that's it. I didn't get to do either."

Deane and law enforcement sources said the incident began about 8:30 a.m., when the student sneaked out of the building and to his mother's car to retrieve the guns. He went first to a bathroom, and as he popped a cartridge into the .30-06 rifle, an assistant principal on routine rounds heard the unmistakable sound of a gun being loaded. The administrator called police, and the school system and police department immediately implemented the county's school violence response plan, put into place after the Columbine shootings.

Officer Bryan Nevitt arrived first with a team of others. He said he looked through a window and spotted the student holding a rifle and speaking to the assistant principal. Nevitt and his team entered the building and caught the administrator's attention. The administrator moved away, and the officers challenged the boy. He complied with their orders and was immediately arrested.

Under the response plan, officers quickly formed a search team, entered the school and began separating possible shooters from possible victims by isolating the armed student and locking down the rest of the school. Police in Colorado were criticized for cordoning off the school and waiting for reinforcements as children inside were being shot.

After cornering the seventh-grader, the teams then went room to room and did not let any students leave until police were certain there were no other weapons. Prince William police trained for months in 2000 for just such an event. Also, every year, each county school goes through a lockdown drill.

Principal William Bixby said all teachers and staff members locked their doors, turned off their lights and got everyone on the floor. Some students were caught between classes. Sarah Ruppert said she was walking to the library with a classmate on an errand for her teacher. She knocked on the locked door and was grabbed by the school's librarian, who told them to run to a back room.

"They were saying, 'Run to the back, run to the back,' " Sarah said. "That's when I saw [the student] outside the library, wearing Army fatigues and a red bandanna." He was also carrying "a big huge rifle," she said.

Most students were escorted from the school before they could gather their belongings to take home for the summer. School officials said students would be allowed in today and Monday and also would be provided counseling. The suspect is a member of a Boy Scout troop, a neighbor said, as is his older brother, who is an Eagle Scout. His father, who works for Mitre Corp., is a scout leader.

The student, a shy, slightly overweight boy who got good grades and liked to play video games, was "the last person you would ever imagine doing something like this," said Rebecca Bare, a neighbor. She is on the board of a homeowners association with the suspect's father.

"He's the one kid you would never have a problem with; the nicest kid in the neighborhood. He would say, 'No, sir' and 'Yes, ma'am,' " she said.

But the student had been hatching a plan, said a woman whose son is close friends with him.

"He said he wanted to take over the school, and he was trying to get other kids to help him," said the mother, who spoke on condition of anonymity because her son was one of several boys he approached. "He'd been talking about it all year."

She said the student told the other boys he was preparing a list of demands that "included a helicopter. He was so imaginative that no one took him seriously, because it sounded like a movie," the mother said. "They thought it was some kid spouting off." The woman's son added, "Most people just kind of ignored it."

Several police cars and a crime scene unit van were parked outside the family's two-level, cream-colored townhouse in Haymarket yesterday afternoon. Detectives were inside and at one point were seen carting out computers and other materials, including bags of guns, neighbors said. No one answered the door at the townhouse.

The boy has been charged with possession of a firearm on school property, possession of a firearm by a minor, use of a firearm in commission of a felony, conspiracy to commit abduction for money and conspiracy to commit murder. He is being held without bond at the Juvenile Detention Home. His mother was being held on $5,000 bond.

Some students said the boy was picked on because of his glasses and clothes and for other reasons.

Staff writers Jerry Markon, Maria Glod and Eric M. Weiss and staff researcher Bobbye Pratt contributed to this report.

Joni Rossman picks up her daughter, K.C. Rossman, 12, a sixth-grader who was evacuated from Bull Run Middle School in Prince William County.Students were evacuated on school buses and taken to nearby Tyler Elementary, where their parents picked them up.