Arlington teachers last night protested changes proposed in the county school board's policy for determining which teachers would be laid off when more schools are closed in 1984.

A new policy, proposed by the school system staff and accepted by the board for further review, would give greater weight to teacher performance and less to seniority in determining layoffs.

Marjorie McCreery, executive director of the Arlington Education Association, a teachers group, said the proposed revisions could lead to large-scale firings and possibly violate contractual agreements.

The revisions would:

* Exempt from layoffs all teachers with "outstanding" performance ratings from the previous year.

* Put RIFed teachers with "successful" ratings in a common pool to be recalled, without regard to seniority and based on appropriateness, before those who received a rating of "needs improvement" or less.

* Exempt at least one teacher in certain schools from being laid off for reasons other than seniority. Exemptions could be made based on the teacher's field of study.

Under the current policy, seniority is a major consideration in determining teacher layoffs. The board adopted new guidelines rating teacher performance last spring.

School Board Vice Chairman Simone (Sim) Pace supported the idea of giving preference to teachers with high performance ratings. When reductions in staff are necessary, Pace said, "I want the best of what I have on staff to remain."

School Superintendent Charles E. Nunley said he supports only the recommendation about exempting some teachers for reasons other than seniority. Nunley said the new performance guidelines will achieve the goal of retaining outstanding teachers.