"We are now in a lock-down," crackled the principal's voice over the PA system.

Teachers quickly flicked off lights, locked their classroom doors and herded students out of view. The students huddled in silence while police and school officials roamed the deserted hallways, peering into darkened classrooms, listening for noises, looking for any movement.

This emergency drill, which had students and teachers practicing what they would do if an armed intruder were on school property, went on for 10 minutes at George Mason High School in Falls Church last spring. Principal Robert Snee says it will be repeated at least four times this school year.

"It's important for kids and staff to guard themselves from what's in the hallway or outside the building," Snee said. "Any school that isn't preparing its students and staff for this possibility is being very foolish."

Raymond Pasi, principal of Yorktown High School in Arlington, disagrees. He has no intention of putting his students and staff through such an exercise. "We can go the route of metal detectors, security cameras, full-time guards and crisis drills, but I think we'll do better with a more moderate approach," Pasi said.

Crisis drilling is becoming part of the new landscape of school safety following April's shootings at Columbine High School in Littleton, Colo. But a sharp debate has erupted among educators and security officials over the value and impact of such drills.

Advocates say that the drills teach students and staff how to respond quickly to the threat of an attack, and that the lessons learned in practices might save lives in reality should an assault ever occur. Critics say the drills are an overreaction and increase student worries about school violence.

The drills are still relatively novel in the Washington area. Falls Church, Manassas and Prince William County are among the few area school districts that have held them or plan to do so.

But that could change soon. Officials in both Virginia and Maryland are considering making some form of crisis drilling mandatory.

Virginia's superintendent of public instruction, Paul D. Stapleton, plans to recommend to a state panel on school safety that schools be required to practice lock-downs periodically, said Cindy Cave, a spokeswoman for the Virginia Department of Education. Stapleton also has asked school superintendents to include crisis drills in their safety plans this school year.

Maryland Lt. Gov. Kathleen Kennedy Townsend (D) last month asked the state's school board to require emergency drills at schools, although she did not specify whether students should be involved. The board likely will adopt the recommendation in some form, said Ron Peiffer, assistant state superintendent.

Crisis drills involving students usually come in two forms: the lock-down, which prepares students for a situation in which it would be dangerous to try to leave the building; and the evacuation, a scenario in which they would have an escape route. Students typically are told in advance exactly when the drill will occur, and teachers or administrators thoroughly explain its purpose.

Another kind of crisis drill that is spreading to more schools focuses on staff and police preparedness, and it is scheduled for when students are not in school. In these exercises, the crisis staged is often very specific. In a drill at Prince William's Beville Middle School, for example, staff members were told that one of their colleagues had been shot by her husband and that he was inside the building.

"The value of an emergency plan comes in being prepared to use it, and one way to prepare is through drills," said James E. Upperman, superintendent of Manassas schools and a supporter of mandatory drilling. "Drills are a common-sense approach to preparing for worst-case scenarios."

But critics say the drills make the likelihood of a violent episode seem greater than it is, adding to children's fears. Many students will conclude that their school would not be holding such practices unless there were a real possibility of an attack, several educators said.

They also expressed concern that some students might become afraid during the exercise itself, despite the advance notice that it is make-believe.

"These drills make kids feel less safe right at a time when we're trying to make schools warm and fuzzy," said Peter Sheras, associate director of the Youth Violence Project at the University of Virginia and a professor of clinical psychology.

Margaret Dunne, director of the Texas School Safety Center, worries that crisis drills could leave students feeling threatened at school, undermining efforts to open channels of communication with their teachers--the most important ingredient to preventing violence, she said.

Pasi, principal at Yorktown, has another worry: that some students might become nonchalant during a real catastrophe, imagining that it is just another practice.

From a security standpoint, some detractors even suggest that the drills might provide information useful to a would-be attacker.

"Do you think it's reasonable and prudent to show students who might be inclined to commit this kind of dramatic violence how you are going to assault the building?" asked Russell Tedesco, director of security services for Prince George's County schools.

Even some drills held when school was not in session have stirred debate.

Two weeks ago, after months of planning, police in Anne Arundel County orchestrated an elaborate drill at Chesapeake High School, replete with scripts, student and faculty volunteers and an arsenal of wooden guns. In the simulated attack, two armed students entered the school, shot one classmate and took another hostage; a SWAT team killed both gunmen and rescued the hostage.

The drill--and the images on TV news of armored personnel storming the school--disturbed some school officials. "It was chilling to see a young lady lying injured in front of the school, even though she was just role-playing," said Huntley Cross, special assistant for student discipline in Anne Arundel schools.

Sheras argues that if schools stage such drills, they should involve only adults. "Mock events are appropriate for training professionals and coordinating faculty and administrators with police, but kids are kids--they aren't good at being coordinated," he said.

But Russell T. Jones, a professor of psychology at Virginia Tech, said his research shows that emergency drills, if conducted properly, can be effective for children, too. The training has to be tailored to different ages so that all students fully understand the rationale behind the drill, he said.

"The skills learned in simulated situations can be really helpful in real-world settings, but the drills have to be developmentally appropriate," Jones said. "The more children understand and appreciate what they're doing, the more they learn with relatively little apprehension."

The Virginia and Maryland proposals for more drills are part of a broader legislative effort in both states to require schools to improve their emergency plans.

For educators on both sides of the issue, the current debate brings back memories of the air-raid drills of the 1950s, which had students cowering under their desks. Officials considering the new breed of emergency drills say they are mindful of that history and do not want to repeat it.

"A lot of us remember the Cold War-era nuclear drills," said Maryland's Peiffer. "It's a chilling memory. You would duck under a desk and you didn't know if you were going to make it home to see your parents. We want to avoid that kind of memory. We don't want to turn schools into fortresses."

Principal John Porter said his school, Alexandria's T.C. Williams High, is debating whether to stage lock-downs this year. "I don't disagree you need to practice, but it's a fine line," he said. "You don't want to overly dramatize a concern and scare people."

It's an issue confronting every principal in the aftermath of the Colorado killings, Porter said. "Since Columbine, we have moved from heightened concern to pure fear. These crisis drills reflect where society's thinking is right now."