Leaders of a work-to-the-rule protest by Fairfax County teachers said yesterday the impact of their job action is escalating as extracurricular student activities are curtailed in several county schools.

School Superintendent S. John Davis, confirming that some after-school events have been discountinued, nevertheless said the teachers' action is having "no adverse effect on the students. I think it's going fairly well."

Paul E. Jenkins, the basketball coach at Woodson High School, said basketball coaches at 24 county schools voted Wednesday night to close school gymnasiums immediately after school. The gyms customarily are kept open for two to three hours after regular class hours.

'We [the coaches] donate our time to keep the gym open," said Jenkins, who said he has been conducting the after-school activity for 17 years.

Jenkins said he closed the gym at 3 p.m. yesterday, which is when the school day ends for Woodson teachers.

Members of the Fairfax Education Association, the organization representing most of Fairfax's 7,000 teachers, voted early Tuesday to stop volunteering for unpaid school-related activities. The move was prompted by teacher dissaticfaction over a 5.15 pay raise for school employes approved Monday by the Fairfax board of supervisors.

Jon White, executive director of the association, said yesterday that teachers at Lee High School have voted not to attend a tea planned for seniors on Sunday.

William E. Jackson, principal at Lee High School, said that as a result of the teachers' vote, the tea for the 450 graduating seniors will be canceled.

A similar Sunday reception for the 400 seniors at J.E.B. Stuart High School has been canceled because the teachers said they would not attend.

Davis, who said he was unaware of the votes by the coaches and the Lee teachers, said school officials are concerned about the cancellation of field trips and dances and plan to take "a stiffer position" to head off such actions.

"Some of those activities are part of the educational process," Davis said.

At a School Board meeting last night, Assistant Superintendent Jacqueline Benson said teachers are being informed that no cancellations would be permitted unless approved by school officials and that no class time or school activity is to be used as a forum to promote or discuss the FEA action.

Many parents interviewed yesterday complained about the teachers' job action. 'If they want to be dealt with professionally, then they must act as professionals," said Frederick Renninger, whose son is a senior at Lee High School.

Several students at Bryant Intermediate School said yesterday they plan to hold a sit-in at the school today in support of the teachers' protest.

The FEA has argued unsuccessfully that its members need a 9.4 percent pay raise to keep up with the cost of living in affluent Fairfax County.

The County School Board gave a unanimous vote of confidence last night to Superintendent Davis, who got a no-confidence vote from the teachers' union on Wednesday.

The teachers vote, resulting from the salary dispute was called "entirely inappropriate" by Board member Ann P. Kahn of Providence District.

Kahn also said only 25 percent of the teachers-those at top scale-will get the 5.15 percent raises, and "the majority are getting 8 and 9 percent."

After each board member in turn voiced support for Davis, the superintendent said he had been shocked by the teachers' action on Wednesday.

"I did not expect it at all," he said. "It shows a level of frustration I and the principals were not aware of. It suggests a frustration out there I underrated and underestimated. I have a commitment to working with employe groups and I appreciate the support of this school board."

Commenting on Davis' statement and the board's action, FEA President Bob Hicks said he felt the teachers message is getting across to the board. "We wanted to dramatize our situation. Our problems are not just financial; there is a growing awareness of our frustration . . ."