"You all know at least one child going tick, tick, tick," the speaker said. "You can feel it. Just looking at that child, you can feel it."

Joseph Harpold, FBI supervisory special agent, paused as his audience of Manassas school and police officials nodded in agreement.

"I have this great fear," Harpold continued. "If we have another Littleton [Colo.] event, I think the wheels will come off our cars; entire school systems will close. So what are we doing to prevent this?"

Harpold's presence yesterday at Metz Junior High School was part of the answer. The FBI-sponsored school violence seminar advised Manassas officials on how to prevent school violence and how to respond if it occurs.

Manassas police and school officials have spent much of the summer revising their emergency response plans, which provide step-by-step instructions on how to deal with situations ranging from bus accidents and power outages to bomb threats and school shootings. In part, the seminar was intended to give schools and police advice on how to coordinate their response plans.

"Schools tend to look at safety issues--how to protect their students, liability concerns--while law enforcement comes at a crisis from a tactical standpoint--how to enter schools and get kids out," said Terri Royster, an FBI behavioral scientist and expert on violent teenagers. "This seminar puts their plans together, gets everyone on the same page."

The seminar, developed in the spring by FBI behavioral scientists in Quantico, distilled the experiences of six police jurisdictions involved in school shootings. FBI agents have presented dozens of similar seminars across the country. Manassas is only the second Washington-area jurisdiction, after Prince William County, to participate in the seminar.

Because of a limited staff, Harpold said, the FBI must reject most of the three seminar requests it receives per day.

City officials argued that the profile was among the most important elements of the seminar.

"We all have ideas of who are the potential shooters and, right or wrong, we have to act on those ideas," Manassas School Superintendent James E. Upperman said. "But we also have to ask: If we're wrong, what are the consequences?"

Harpold, whose granddaughter is in the Manassas school system, said one of the most important preventive mechanisms is an anonymous student tip line, because every school shooter to date has shared his plans with peers. Manassas schools have two tips lines, Upperman said.

Upperman said the district's seven schools will practice emergency evacuations to test their new response plan. In a safety committee of Virginia's Department of Education, he has proposed that similar emergency testing be made mandatory in all Virginia public schools.

One person said of school violence, "This could never happen here."

Harpold responded to that sentiment with an anecdote. In preparation for a getaway, the Jonesboro, Ark., shooters filled a van with camping gear, additional weapons and food to last 30 days.

"Next to thousands of rounds of ammunition, investigators found a bag of Doritos," Harpold said. "Really brings home the idea that these are juveniles, doesn't it?"