About 3,000 Fairfax County students, many of them cutting classes, jammed lobbies and hallways at two high schools yesterday morning to stage demonstrations in support of higher pay for their teachers.

Many of the county's 8,000 teachers are in the midst of a work slowdown because of the county's refusal to agree to their demands for higher salaries.

At Lee High School in Springfield, all but 200 of the school's approximately 1,700 students occupied the entire second floor during second period, between 8:45 a.m. and 9:35 a.m., according to Principal Frank Elliot.

Elliot said he ended the demonstration with an announcement at the end of second period. "I just laid the consequences on them and told them that each student absent from class would be counted as having a class cut. I think that got the point across."

At Hayfield High School, south of Alexandria, about 1,500 students congregated in the gym lobby during a 10-minute break between second and third periods, said Associate Principal Bill Caudill. No classes were disrupted.

School spokeswoman Dolores Bohen said no demonstrations were reported at other Fairfax schools.

Donna Caudill, president of the Fairfax Education Association, said that the group, which called for the job protest, does not approve of any student actions that disrupt classes. Even so, she said, "Teachers do appreciate the sentiment."

The sit-ins came on the third day of a "work-to-the-rule" action taken by the association, which represents about 85 percent of Fairfax teachers, and the smaller Fairfax Federation of Teachers. Contending that the school system's offer of a 4 percent pay increase for next year is inadequate, the teachers have refused to work more than the 7 1/2 hours a day mandated by their contracts. They say their members are declining to spend extra time grading papers, volunteering to lead extracurricular groups, and other activities often performed after class hours.

A beginning teacher in Fairfax earns $18,385 a year.

Bohen said yesterday that no serious disruptions of school routine have taken place because of the job action. She noted that teachers are required by Virginia law to perform all duties requested by principals regardless of the time of day.

Kevin Bell, president of the Fairfax Council of Parent Teacher Associations, said Superintendent Robert R. Spillane had told him principals will insist that teachers write college recommendations and perform other essential, nonclassroom tasks.