A 13-year-old boy was critically wounded outside a Prince George's County school yesterday in a shooting that authorities linked to a spate of sniper attacks that have now killed six people and wounded two others in the Washington area since Wednesday.

The youth, an eighth-grader at Benjamin Tasker Middle School in Bowie, was struck in the chest by a high-powered rifle bullet as he was being dropped off in front of the school by an aunt about 8 a.m., authorities said. An investigator said police found a spent shell casing in woods about 140 yards from the school, in a spot with a clear sightline to where the boy crumpled to the ground, bleeding.

"We have a level of fear that we're not used to," Montgomery County Police Chief Charles A. Moose said yesterday when it became apparent that Prince George's had joined the list of Washington area jurisdictions where sniper attacks have occurred. The others are Montgomery, the District and Spotsylvania County.

Speaking to reporters in Rockville, his eyes moist and his voice quivering with anger, Moose said: "Today it went down to the children. . . . Someone is so mean-spirited that they shot a child. . . . Now we're stepping over the line. Shooting a kid. I guess it's getting to be really, really personal now."

The boy, hospitalized last night in critical but stable condition after about 2 1/2 hours of surgery, is the youngest of eight sniper victims. The first, a 55-year-old man, was slain Wednesday night in Montgomery. Four people, ages 25 to 54, were killed Thursday morning in Montgomery, a 72-year-old man was fatally shot Thursday night in the District and a 43-year-old woman was wounded in Spotsylvania on Friday afternoon.

All the victims were in public places going about ordinary activities -- mowing a lawn, filling a gas tank, walking into a supermarket. But the shooting of a teenager in front of his school jolted parents and school systems across the region and raised an already intensive police investigation to a new level of urgency.

Maryland Gov. Parris N. Glendening announced that the state would contribute $100,000 to an existing $50,000 reward fund for information leading to an arrest and conviction in the case. In Prince George's and Montgomery, officials said schools would open today with greatly increased security and no outdoor activities for students. And in an extraordinary joint appearance last night, the Montgomery, Prince George's and District police chiefs and other law enforcement officials vowed to work cooperatively in one of the biggest criminal manhunts in the region's history.

Calling the attacks "cowardly and senseless," President Bush said federal law enforcement agencies would continue assisting local investigators. "Laura and I send our thoughts and prayers to the victims and their families," the president said.

Homeland Security Director Tom Ridge said federal authorities have no evidence that the shootings are the work of an organized terrorist group. "It's a horrible tragedy," Ridge said. "You get nauseous thinking about how cowardly, how inhumane this is."

At the Bowie school, police and anxious parents poured into the area following reports of the shooting, and scores of officers and police cadets began searching for evidence, focusing on woods nearby. Meanwhile, surgeons at Children's Hospital worked to save the critically injured youngster. The bullet had penetrated his upper abdomen before fragmenting and causing damage to his spleen, stomach, pancreas, lungs and diaphragm, hospital officials said.

After conducting ballistics tests yesterday, authorities declined to say whether the bullet in the Bowie attack had come from the same high-powered .223-caliber rifle used in previous attacks. Michael Bouchard, head of the Baltimore office of the federal Bureau of Alcohol, Tobacco and Firearms, would say only that the slug was from "the same family of bullets" as the ammunition in earlier shootings.

Yet officials made it clear that they had evidence tying the Bowie shooting to the sniper attacks in Montgomery, the District and Virginia.

"The shooting this morning in Prince George's County is linked," Chief Moose said. "The ballistics, the evidence, the science tells us that."

Authorities, citing ballistics tests, have said that the same rifle was used in three of the Montgomery killings, the D.C. slaying and the shooting in Spotsylvania. The bullet fragments from the other two Montgomery slayings could not be accurately tested.

In Bowie, Mark Jones, who lives across the street from the Tasker school, said he heard a loud noise from nearby woods as he walked from his house about the time of the shooting.

"I heard . . . 'pow,' " Jones, 38, said later, pointing to the woods. "And then I heard a woman screaming" near the front entrance of the school. But when he looked toward the woods after hearing the noise, he said, he saw no movement. So he shrugged and went about his daily business.

Prince George's Police Chief Gerald M. Wilson confirmed that police received calls from several people who said they saw a white vehicle leave the area after the shooting. Some people described a truck, others a van, police said. Since Thursday, investigators have been searching for a white box truck that a witness in Montgomery reported seeing speed away from one of the shooting scenes there.

Later in the day, as schools in the Washington area were locked down and outdoor activities were canceled, the fear became apparent, as did the pressure authorities face in trying to come up with a break in the case.

Montgomery County Executive Douglas M. Duncan said at one of numerous news conferences he held yesterday: "The community is in a state of fear, a state of anxiety. . . . It's a very fearful time.

"People are very nervous and very anxious, but they are going to work," he added. "As people are very fearful, they're going about their routines as best they can. Working together, we are going to crack this as soon as we can."

At the hospital, doctors said the boy, who was breathing with the help of a ventilator, had a good chance of survival, although his condition could change significantly throughout the evening. The boy's identity is being withheld by authorities because he is a witness.

"We did take out his spleen, a portion of his stomach, a portion of his pancreas, so he has lost several organs at this time," said pediatric surgeon Martin Eichelberger. "But those are organs all of us can live without."

At a news conference, Moose said he sent a letter to the Justice Department asking for federal assistance under what is known as the serial killings law.

According to a Justice Department spokesman, the statute makes clear that the federal government can provide the assistance that it has already been furnishing in the case. He said Justice and the FBI "are committed to whatever possible and appropriate assistance we can provide."

Normally, crimes such as murder are offenses under state law and are investigated without federal involvement.

Chief Wilson said: "The young man was dropped off at the school, there was a gunshot, his aunt turned around and he was lying on the ground. He apparently told her that he had been shot."

He added that the only witnesses were a couple of students and the boy's aunt. He said that because of the boy's condition, investigators have been unable to interview him. He said that they have no information on how far away the shooter might have been when he fired. He said police were interviewing the student witnesses.

Audrey E. Scott, a County Council member representing Bowie, who lives two blocks from the school, was at Bowie Health Center with the family immediately after the shooting. "This is right in my back yard," she said. "It's staggering."

Scott said that the boy lives with his mother and that his aunt drove him to the school. She said the aunt had just dropped him by the front door. The boy had gotten out of the car, wearing his backpack, and the aunt had driven a few feet when she heard a loud noise.

Scott said the aunt turned around and saw the boy fall down. She stopped, got out and rushed to him. The boy stood up again and tried to get in the car, the council member said.

"She had gone 10 or 20 feet, and she heard the gunshot, and she turned around and she saw the boy on the ground," Scott said. "She jumped out of the car and he was trying to get up, trying to walk.

"There was a wound on the left hand side of the chest, next to the boy's heart," Scott said.

Meanwhile, in the District, where one of the slayings took place, Police Chief Charles H. Ramsey said that police dogs trained to sniff out gunpowder or explosive residue were "alerted" to a wall about 80 yards from the site where Pascal Charlot, 72, was shot to death Thursday night in Northwest.

The wall bears the sign for Northminster Presbyterian Church, at the nearby corner of Alaska Avenue and Kalmia Road NW.

Pastor Leonard Lassiter said that police told him Sunday that they would be "exhaustively" checking the five-foot wall, and possibly removing bricks to test them. The wall sits under a tree, in a fairly dark area with a clear line of sight to the well-lit corner where Charlot was killed with a single shot about 9:20 p.m.

The shootings triggered increased activity and patrols among federal law enforcement agencies and D.C. police, including an e-mail advisory circulated to congressional staffers from House Sergeant-at-Arms Bill Livingood "to reduce outside activities to the extent possible."

"There is no indication that a threat is directed toward the Capitol or Members of Congress," the e-mail stated. "However, we are asking everyone to exercise an abundance of caution at work and at home until the situation is resolved."

U.S. Capitol Police, D.C. police and others stepped up precautionary measures.

D.C. police increased patrols around schools, instituted routine checks with school administrators about suspicious incidents and intensified helicopter and harbor patrols, Officer Quintin Peterson said.

Day shifts for officers were lengthened to accommodate the hours when children are let out of school, and police publicized a $10,000 reward for any information leading to the arrest and conviction of the killer or killers.

Staff writers Eugene L. Meyer, Tracey Reeves, Annie Gowen and Monte Reel contributed to this report.