The possible presence of undercover policemen impersonating students in Fairfax County high schools has created "an atmosphere of tension and potential violence," according to a student-circulated petition, led to a sit-down demonstration at Chantilly High School and made things difficult for new students suspected by others of being "narcs."

"There is a lot of suspicion and doubt in the schools. New kids all feel ostracized and harassed," said A. Lewis Lowery, a Langley High School senior and the student representative on the Fairfax County School Board.

Lowery said he plans to make a formal complaint against the undercover policemen at a school board meeting tonight and ask the board to rescind its policy allowing them in the schools.

Fairfax Police Chief Richard A.King said yesterday there are currently no undercover police in any county High school and that there have been none since they policy allowing them in the schools was announced in March. King said in March that "one or two" undercover agents were placed in county schools this year.

Nine student leaders in county schools and about 20 other students interview recently said part of the reason tht students are upset about 'narcs' in schools is because so many students smoke majijuana. Although legal penalties are harsh, most students consider the drug"no big deal." Many students said they believed they can function is school, on tests and in discussions, just as well when they are "high" as when they are 'straight'.

Across the country last year, one of every 11 high school students smoked pot every day, according to the national Institute on Drug Abuse. Fairfax school principals say they have noticed an increase in the number of students who are high in class.

"You know I don't have any great talent," said one Chantilly High Junior recently. "I'm not smart in school. I'm not a good athlete. I like to get high because it makes me relax in school. I like the things that I think when I'm high."

Dr. Robert S. Peterson, of the research division of the National Institute on Drug Abuse, said yesterday students who habitually smoke marijuana in school are likely to miss out on intellectual and social skills that would help them adjust to being an adult.

To control widespread drug use, the Fairfax county school system and the county Police annnounced March 21 that undercover policemen may be enrolled in county high schools 'as a last report' to stop drug traffic and use. School officials an police also announced a new, tougher suspension policy that calls for an automatic five day suspension of any student caught using, possessing or exchanging an illegal drug or alcohol.

School Superintendant S.John Davis said then that the undercover program was announced publicly "because we are coming out front. We don't want to trap students."

It was learned yesterday, however, that Davis decided to announce the program, which was originally intended to be kept secret until this summer, because county high school students had found out about it.

Several members of the Student Advisory Council, an organization of elected representatives from the county's 22 high schools, said yesterday that Davis' announcement in March has caused distrust in their schools.

Judy Chiang, a student representatives from Herndon High, said, "The first week after the announcement people kept coming up to me and saying they saw people who looked 'funny' to them." At Groveton High, student representative Elizabeth Vandenburg said there is a widespread fear in the school that there are undercover police there.

A new student at Chantilly High School, where 15 students have been suspended on drug-related charges in the past three weeks, said yesterday he had had difficulty making friends. He siad students have been "very cold" toward him.

The student, who didn't want to be identified, enrolled at Chantilly High shortly before the undercover program was announced. "I've heard kids say in the halls about me," That kid is new, I bet he is a narc."

At Chantilly High the paranoia has taken on comic dimensions. Shortly after the announcement about undercover agents in schools, students there began suspecting a new janitor. One student overheard the suspect janitor ask another janitor, "Where's my gun?" Students said that janitor was universally avoided until word got around that the reference was not to a firearm, but to a staple gun.

The sit-down demonstration held April 17 at Chantilly High School involved about 70 students protesting the drug - related suspensions at the school. Fifteen students were suspended after uniformed marijuana in a special smoking section of the school.

The student protesters said the police did not follow school guidelines when they reported the students to school authorities and they disapproved of the possible presence of undercover police in the school.

The demonstration ended after five student spokesmen were selected to bring their complaints to the principal, Robert Davis.