The Fairfax County Board of Supervisors voted 5 to 4 yesterday to raise supervisors' salaries by more than $13,000, to $35,000 a year starting in 1988.

Under the plan, which is by far the largest raise the county board has ever given future board members, the salary for a supervisor would then be increased annually until it reached $45,000 by 1991.

The 59 percent increase, the board's first in seven years, was intended to bring salaries for the county's nine supervisors in line with those of lawmakers in other large localities in the Washington area. The new salaries, based on the recommendations of the Fairfax County Chamber of Commerce, will not affect board members in the current term, but will apply after the November 1987 elections when the new board takes office.

Opponents of the pay raise were far more vocal than supporters. "There's been no movement of people breaking down my door" in support of a pay raise, said county board Chairman John F. Herrity, a Republican. Herrity said the increase would lead the public to expect a full-time commitment from local legislators, and discourage small businessmen who want to be part-time legislators.

"God deliver us from full-time politicians," said Herrity, who said in an interview that he spends "at least 40 to 50 hours a week" on county business. He also owns an insurance business.

Board Vice Chairman Martha V. Pennino (D-Centreville), who supported the salary increase, took issue with Herrity. She called the raise "not at all unreasonable." Referring to the $35,000 sum, she added, "And in today's world in Fairfax County it's not a full-time salary."

Supervisor Audrey Moore (D-Annandale), who voted for the increase, asked board members who opposed it if they would nevertheless accept the raise if they are reelected.

"I guess we'll have to wait and see, Mrs. Moore," said Herrity, who added a few minutes later, "I think that's our business, not yours."

Other supervisors have said that their current salaries are inadequate considering the demands made on lawmakers in a jurisdiction the size of Fairfax, and have maintained that the low pay discouraged would-be office seekers. The county's population is about 680,000.

Fairfax supervisors make $21,589. That is about $10,000 less than Prince George's County Council members, $16,000 less than Montgomery County Council members and $26,000 less than District City Council members.

All four board Democrats voted for the pay raise, and all but one Republican, T. Farrell Egge of the Mount Vernon district, voted against it. Three of the supervisors who voted for the raise have no other employment.

Voting for the salary increase were Joseph Alexander (D-Lee), Egge, Moore, Pennino and James M. Scott (D-Providence).

Voting against were Thomas M. Davis III (R-Mason), Nancy K. Falck (R-Dranesville), Herrity and Elaine McConnell (R-Springfield).