From the moment you walk in the front doors of Seneca Valley High School, Big Brother has his eyes on you. Take a few steps in, and Ellen Beckwith, dressed in a security uniform and sitting behind a neat desk, will size you up: If you're wearing a hat, you'll immediately be branded an outsider, someone unaware of the school's no-hat policy for its 1,500 students. Refuse to sign in, and Beckwith will send you on your way.

"Their body language really tells you that they're not supposed to be here," she said.

A stroll to other entrances will find them locked.

Once properly signed in, an identifying badge stuck on your chest, your movement will be silently watched by a phalanx of color video cameras, hidden in black plastic globes that hang from the ceiling. If you attempt to break in after-hours, your every step, every jiggle of a doorknob or locker, will set off motion detectors and trip alarms.

This is a Montgomery County school in a new era.

Although a report to be released today finds that most students, teachers and parents think the schools are relatively safe, and although the number of violent incidents has decreased over the last decade, Montgomery County schools are confronting a different kind of violence in a changing world, one where easy access to weapons has made fights more dangerous. Senior pranks have gotten vicious, and students have become killers.

The challenge for Montgomery County, says the author of the report, isn't safeguarding the school from violent intruders, but being prepared for the threat from within.

"It's a different world now," said school board Vice President Patricia O'Neill (Bethesda-Chevy Chase). "Columbine showed us that."

The news in April that two students went on a shooting rampage in Columbine High School in Littleton, Colo., a suburban Denver community that looks a lot like Montgomery County, shook Superintendent Paul L. Vance to the core.

"I never thought at any point in my career I would recommend electronic cameras in schools," Vance said of his $685,000 proposal, quickly approved by the school board, to place sophisticated video cameras in all 23 high schools. "But we've never had anything like this before in America.

"School violence heretofore was associated with disadvantaged youth," he said. "And now, all of a sudden, we're seeing ghastly behavior in what had been the promised land, among the people who fled urban violence, in upper-middle-class families. The best and the brightest. That is new and very frightening."

Indeed, about 200 knives were taken from Montgomery students in the past year. Two youths were arrested last year after one of them made a bomb and the other brought it to Rocky Hill Middle School. And just a few weeks ago, six Churchill High students were arrested after they allegedly destroyed the gym floor and scrawled graphic graffiti on walls and stairwells.

Students at Montgomery Blair High School now are issued identification cards, and a uniformed police officer has been assigned to Gaithersburg High. Some principals in older schools wish their offices had back doors, as all new schools do, for a quick escape if someone comes to threaten them. Others want to install keyless locks with coded cards. "If Holiday Inn can do it, why can't we?" asked Gaithersburg High School Principal Fred Evans.

But, principals say, their efforts to heighten security are met with community fears that the measures mean the schools are going downhill. There is also the realization that such efforts alone aren't enough. Even though his school is going to get the cameras, Gaithersburg's Evans isn't sure he wants them. "I am of the firm belief that safety and security of the school is enhanced when people are communicating with each other," he said, "when students can come to an adult and say, `This is going on. You need to fix it.' And effective instruction, and giving students activities, resolves a lot of discipline problems."

Evans has formed a committee of parents and community members concerned that having a uniformed police officer makes the school look bad. They are deciding whether to have the officer back next year. Beckwith has been stationed at Seneca Valley's front door since May 10, when a bomb scare, albeit a hoax, kept thousands of students out of school.

Wayne Whigham, principal at Seneca Valley, said he was careful to sell the community on the idea of video cameras before using profits from the school store to install them.

"A lot of PR went into this effort. You want your community behind you. You don't want people saying, `Oh, no, what's wrong with Seneca Valley?' " Whigham said. "Cameras aren't going to stop something like Columbine. But they're a technology that's available to make schools safer."

At Seneca Valley and at Damascus High School, video cameras have helped catch students making bomb threats, vandalizing school property, stealing and fighting. At Seneca Valley, they defused a potentially explosive situation by helping to find and stop a troubled student writing racist graffiti on a bathroom wall.

"There's been a calming effect since the cameras were introduced," said Michael Gough, director of student security, who said it would cost millions of dollars to hire security people to monitor the areas that cameras can. "We're spending $35,000 a year just in supplies to clean up graffiti in schools. It would be worth it to catch just one or two students."

Harder than monitoring vandalism is recognizing and defusing the sorts of internal problems that led to the tragedies of Columbine, Paducah, Ky., Jonesboro, Ark., Springfield, Ore., and other suburbs where lonely outcasts have massacred fellow classmates.

Who knows what twists a student's soul to make him wish death on others? But teachers, counselors and principals can at least listen to students to know what's going on. Internal intelligence is what Pete Blauvelt, head of the National Alliance for Safe Schools and author of the security report, calls such networking with students. And, he said, Montgomery County schools are not doing nearly enough of it.

"We didn't find internal networks in place. We didn't find small group discussions going on at all," he said. "Columbine created a sea change for us in how we look at schools. I'm not here to create paranoia, but if you want to know what's going on in your schools, you've got to talk to kids. They'll tell you. You can't afford not to know."

Blauvelt's report, a survey of 32 Montgomery County schools and five special centers, found other security problems as well. In his first assessment, in 1992, Blauvelt recommended that every school have its own safety and security staff, which the board later hired. But now, he says, that staff -- which includes veteran Montgomery County police officers -- isn't really allowed to do its job.

"They're monitoring cafeterias, making sure students don't park in teachers' designated spaces; they're monitoring the timeout room. All of which is a waste of time and energy as far as I'm concerned," Blauvelt said. "They should be conducting investigations into assaults and thefts."

Instead, in most cases, those investigations fall to assistant principals who are not trained investigators, he said. And the way they report incidents is a "mishmash."

"We were unable to really figure out how the system worked," Blauvelt said. "It was awfully discretionary on the part of the administrator as to what got reported, who got involved and who got notified. I find that a little disquieting. There needs to be a written standard procedure."

And when it comes to emergency management plans, again Montgomery County schools are lacking, he said.

"Their plans are very, very fragmented," Blauvelt said. "Most of them dealt with bomb threats and fire drills, and that's just totally inadequate."

Instead, schools now need to have plans to deal with hostage situations, shooters stalking the hallways, toxic waste spills, and irate parents or employees who get out of control. And schools need to practice those plans.

"Montgomery County is still very blessed with the perception that schools are the safest place for kids. I think that's good," Blauvelt said. "But things change. We have to begin to deal with the unthinkable."