Arlington school officials have devised a way to get some of those much sought-after mini-computers for free.

School Superintendent Charles E. Nunley got permission from the School Board last night to allow a Northern Virginia firm to stage a summer "computer camp" at a county school for free in exchange for use of computers during the school year.

"It's a scheme that has mutual benefits," said Karen Rosenbaum, a spokesman for Technology Import Corp. of Arlington. Under a plan Nunley presented to the school board the firm would allow the schools to use 30 microcomputers, valued at more than $25,000, if officials allow it to use three classrooms and other facilities at Washington-Lee High School for the summer camp.

The plan is considered a boon by budget-conscious Arlington officials who have resisted public demands to put more computers into the schools because of the costs involved. With a $47,000 budget for computers, Arlington is trailing other area schools in its computer purchases.

School Board Chairman Evelyn Reid Syphax said she wants to insure that students from all of the county's high schools have a chance to use the equipment. The firm said it is planning four two-week sessions at the school that should draw about 400 youngsters for three hours a day in computer instruction plus athletic programs. The camp would cost $150 a week.

Parent and community groups throughout the Washington area recently have begun pressing school officials to buy more computers and offer more students courses in their everyday uses.

John Tuccillo, head of an Arlington group that has purchased computers for an elementary school and paid for teacher computer training, said that he supports the camp plan. "This is the kind of movement we need," Tuccillo said.

In other action last night, the school board revised its policy for determining what teachers shall be subject to layoffs, deciding to allow certain schools to exempt at least one teacher from RIFs for reasons other than seniority.

After heated protests from teacher representatives, the board rejected two other proposals that would give more weight to teacher performance than seniority in deciding what teachers may be laid off this year because of declining enrollments.

Board Chairman Syphax said she supports the current seniority system but is concerned about losing good teachers who are new to the county schools.

The board also refused a plea by teachers to reconsider last month's decision to oppose legislation that would authorize collective bargaining between teachers and the school system.