Fairfax County School Superintendent Robert R. Spillane rejected yesterday a PTA proposal to reopen teacher salary negotiations, and students at three county high schools held demonstrations in support of higher pay for teachers.

The demonstrators supported teachers' protests against Spillane's salary recommendation to the School Board, which combines a 4 percent cost-of-living increase with pay raises for new teachers and the most experienced teachers. The teachers contend that those in the middle of the pay scale would see little gain.

Two associations representing 85 percent of the county's teachers began a "work-to-the-rule" slowdown last week, refusing to perform duties outside of school hours.

Spillane has said that the protest is having little effect, but the Fairfax Education Association, the larger of the two teacher unions with 6,300 members, said that numerous student activities had been rescheduled for school hours or canceled.

Wednesday, the county Council of PTAs voted to urge higher salaries than Spillane recommended, and to propose that representatives of the superintendent, the teachers and the Board of Supervisors, which has final approval of the school budget, meet to reopen salary talks.

Spillane, through spokeswoman Dolores Bohen, rejected the proposal.

"He feels his part of the process is finished," Bohen said. "If the School Board wants to adopt something other than what he recommended, that's fine."

At West Springfield High School, about 600 of the school's 2,400 students sat down in the hallway for 40 minutes during a class period, some chanting and shouting, said D.A. Sims, president of the school's senior class. The protest ended when administrators asked the students to return to class, he said.

More than 100 students stood in front of Herndon High School for 25 minutes, some holding a banner, to show their support for higher pay for teachers, said Dennis F. Houlihan, a school administrator. He said the protest was "very orderly" and the students did not miss any class time.

Some students at Mount Vernon High School south of Alexandria staged a brief demonstration, said Assistant Principal Jack Robertson, but "they decided the best thing to do was go to class after we explained that was not the best thing to do to support teachers."

At Oakton High School, teachers persuaded students to call off a planned protest, Assistant Principal George B. Griswold Jr. said. The same thing happened at Falls Church High School, said PTA President Marsha Reiser.

Patrice Gancie, a spokeswoman for the Fairfax Education Federation, said the organization has urged students not to hold demonstrations that disrupt classes.

Yesterday's protests followed earlier sit-ins at three other county high schools: Fairfax High, Lee High and Hayfield Secondary.