Between 150 and 200 students at Fairfax High School walked out of their school briefly yesterday, protesting the refusal of county supervisors to grant more than a 5.15 per cent cost-of-living pay increase to their teachers.

The protest at the Fairfax City school was the fourth in recent days at a school run by the county school administration over the pay increases. Officials of the 6,500-member Fairfax Education Association have called for a work-to-the-rule protest by teachers, but have disapproved the student walkouts.

Instead of going to an 11:40 a.m. class the Fairfax High protesters walked out of their modernistic school and gathered in small groups on the grassy campus for 20 minutes.

"Come on! Come on! Come on!" shouted junior Pam Simmons, one of the protest organizers, to her fellow students. But most of the 1,600 students at the school decided to stay in the building and go to their next class.

The protest came a day after a similar one at Oakton High School and followed earlier protests at Herndon High School and Bryant Intermediate School in the county.

At Fairfax High yesterday, as word of the planned walkout circulated among students, principal Clarence P. Drayer warned over an intercom system that any such action could lead to disciplinary action, including suspension.

In an impromptu meeting with Simmons and another protest leader, 12-grader Chuck Swett, Drayer had said:

"I'm not arguing with your doing something. I wish you would. But it's what you do. We're trying to teach you to do things in the right way, in a way that will be accepted and get the right results. But I don't think this is going to get the right results."

Earlier, another protest organizer, 11th-grader Mary Donahue, said "we've been planning it for a couple of weeks . . . We're doing it against the Board of Supervisors." The 5.15 percent pay increase was proposed by the school board and, in effect, approved by the supervisors when they adopted a budget cutting 10 cents off the real estate tax rate.

Fairfax High principal Drayer said the protesting students and many others were not fully informed about the pay increases. He said that counting pay increases that are based on years of service and educational training many teachers will get large salary increases.

According to Superintendent Davis, 29 percent of the county teachers will receive 9 percent or more increases next year, 41 percent will get 8 percent or more, 4 percent will get 7 percent or more, and 26 percent will get only the 5.15 percent.

In a separate development, the teacher's association filed a suit yesterday in U.S. court in Alexandria, alleging that Groveton High School math teacher Charles Rayburn's right of free speech was violated by county school officials. Rayburn, former head football teacher at Groveton, was relieved of his coaching duties last November after he criticized the school's athletic program in a published interview.