Representatives of Fairfax County's largest teacher group, saying members are frustrated by an "unacceptable" 4 percent pay increase offered for next year, said yesterday the group would begin a work slowdown tomorrow.

The 6,300-member Fairfax Education Association, which represents 85 percent of the county's teachers, principals, aides and secretaries, voted 4,242 to 508 to "work to the rule," or refuse to perform duties outside school hours.

The expected result of the action is to cut down on the amount of extra time teachers put in grading papers, planning for courses and helping with volunteer extracurricular activities such as language clubs or field trips, said FEA President Donna Caudill.

"If the school system believes we can do our job in the 7 1/2 hours they give us, then that's what we're going to do," she said.

Fairfax County School Superintendent Robert R. Spillane was out of town yesterday and unavailable for comment.

His office issued a prepared statement saying that principals would be instructed to continue existing programs, and to make certain that school requirements are met during the official 7 1/2-hour day.

In a related action, the 850-member Fairfax Federation of Teachers -- the county's only other teacher association -- will meet tomorrow to consider a motion to approve work-to-the-rule and other actions, including possible informational picketing, according to Rick Nelson, the group's president.

For Guy Wilson, a guidance counselor at Falls Church High School, the FEA action means he will be less available to students, if he is to find quiet time during the school day to write college recommendations.

Instead of lingering in his office until 4:30 or 5 p.m., he'll leave school at 3 p.m., he said.

For Judy Grumbacher, a physics teacher at the same high school, work-to-the-rule will mean forsaking the usual two hours she said she spends at home each night planning lessons, grading homework and reading professional journals.

"I'm real torn by this because you can't do the kind of job that I think the kids deserve, or that I want to do, on contract hours," she said, echoing Wilson's complaints. "And, yet, I think that it's important that people in the county understand what the situation is."

At issue is Spillane's latest teacher pay package for the next school year, which would raise the average salary from $29,275 to $31,412. It also would boost starting teacher salaries from $18,385 to $20,000, and provide a 4 percent cost-of-living increase.

The FEA, which initially asked for 20 percent raises, lowered its request to 8.8 percent by the time talks broke down two weeks ago. Although Caudill said she applauds increases for starting and veteran teachers, she maintained that two-thirds of the county's teachers would not receive substantial pay raises.

She also has said that entry-level salaries should be at least $25,000 a year to attract top talent.

"Dedication isn't enough to pay the bills," she said.

It is the first time since 1979 that the group has voted a work slowdown, said Caudill.

The FEA last year approved such an action, but called it off at the last minute when the county offered extra money.

Last night, the executive board of the Fairfax County Council of PTAs approved a resolution urging top priority for greater teacher pay, but not supporting a work-to-the-rule action, council President Kevin Bell said.

The resolution is to be presented to the full council Dec. 11, he said.