Freshmen in Arlington high schools will be forbidden to leave school grounds at lunchtime starting this fall with the unanimous decision of the County School Board late Thursday night to phase out its "open-campus" policy.

In the fall of 1984, sophomores also will be covered by the lunchtime restrictions, with one grade level added per year subsequently.

Thus, in four years there will be no "open campuses."

Currently, high school students who have written parental permission are allowed to leave their schools at lunchtime.

The practice has been criticized by law enforcement officials and some parents who contend it has contributed to delinquency and drug and alcohol abuse.

However, many parents and most students have argued that the law-abiding majority should not be penalized for the misdeeds of a small minority.

Students who have valid reasons for leaving, such as those involved in work-study or career-center programs, will not be affected by the new policy.

However, unlike the old policy, which covered only the three regular high schools, the new policy will also apply to H-B Woodlawn Secondary School, an "alternative" school with grades 7 to 12 that has a college-style format.

While the "open campuses" are being eliminated, parents who want to allow their children to leave school grounds at lunchtime will have to sign a written permission slip at the school.

Students given permission will be issued photo identification cards to be paid for by themselves or their parents.

The board deferred action on tightening attendance policies until the administrative staff can study the issue further, including the possibility of after-school detention periods to make up unexcused absences.

On another matter, the board voted to hold an executive closed-door session next week to complete an evaluation begun last March of controversial Superintendent Charles E. Nunley.

Board chairman Evelyn Reid Syphax declined to comment yesterday on whether the board may act as a result of the evaluation, saying, "I can't say that his job is at stake. We're just completing an evaluation we did not complete earlier."