The president of the Fairfax Education Association, which claims a membership of 6,500, or 85 percent of Fairfax County public school teachers, said last night a work slowdown may be undertaken unless there is progress in contract negotiations by Friday.

The tactic, called work-to-the-rule, would mean that teachers would refuse to work more than the 7 1/2 hours mandated in their present contract and forgo extracurricular activities, grading homework at home and other tasks frequently performed after the close of the school day.

FEA President Donna Caudill said the organization agreed to consider such a move at a meeting at Woodson High School last night attended by about 1,000 teachers.

The slowdown would be undertaken following a vote of the members. A strike would be illegal under Virginia law.

The FEA members agreed to wear green to classes this Friday as a show of support for the organization, Caudill said.

The FEA is seeking increased salaries for new teachers, who now are paid $18,335 a year, second-highest in the Washington area, and 20 percent pay raises for other teachers.

The average teacher pay in the county is now about $29,000 a year.