The Fairfax County School Board, squeezed by tight finances in the midst of a recession, adopted a budget for the 1991-92 academic year last night with the smallest percentage increase in more than a quarter-century.

The board barely tinkered with Superintendent Robert R. Spillane's $903.7 million spending plan, which represents a 3.2 percent increase over this year. However, the board did manage to restore several modest cuts Spillane had suggested and stashed $3.1 million in reserve to cushion the area's largest school district against future bad economic news.

With so little money available for initiatives, the board approved the budget in less than an hour -- apparently a record time, according to longtime officials -- and with none of the serious donnybrooks of previous years.

"This is not a brouhaha year," said member Letty A. Fleetwood (Providence).

Indeed, last night's unanimous vote was an anticlimactic finale to a budget season that started with fireworks.

When he first unveiled his proposal in January, Spillane resurrected a previously defeated plan to extend Mondays to a full school day for elementary students. The move sparked an uproar among some School Board members, who called it an act of insubordination, and among parents and teachers, who considered the issue decided.

Eventually, Spillane withdrew the plan, allowing the board to avoid revisiting the deeply divisive issue and freeing the $3.6 million he had earmarked for the plan.

The budget includes no cost-of-living raises for teachers or other employees; cuts spending on capital projects, printing and school system cars and trucks; freezes nearly all other spending to current levels with no allowances for inflation; and eliminates 60 central office positions.

The board largely restored funding for two items cut by Spillane: eight of 12 special projects teachers used in schools with large enrollments with special needs, such as non-English-speaking students; and four intermediate school assistant principals. Using money from the aborted Monday plan and by cutting $552,000 from the budget for substitute teachers, the board put $3.1 million in reserve because the state legislature has not decided how much to cut aid to local schools.

In eliminating cost-of-living increases, the school system broke with a history of awarding teachers 30 percent raises over three years in the late 1980s as part of the merit pay plan.

Eligible employees will still receive regularly scheduled seniority step increases, averaging about 3.8 percent for teachers. However, about a third of the county's 8,500 teachers are at the top of the scale and will not receive any increase.

The board essentially ignored union pleas for additional compensation, even as an $8,000 radio advertisement campaign by the Fairfax Education Association ended yesterday. Union leaders had expected a proposal to add longevity steps for experienced teachers, but no member made such a motion.

"This is our worst-case scenario," said Maureen Daniels, association president.

In related actions, the board rejected on a 6 to 3 vote a move by Vice Chairman Laura I. McDowall (Annandale) to freeze the salaries of Spillane and his top aides. Instead, as has been the custom, the board will decide at its summer retreat whether to award raises to high-ranking officials.

The budget now will go to the Board of Supervisors, where it usually is approved with no changes. However, some supervisors have suggested they may try to reduce education funding.

In a letter last month, the chairman of the board's Citizens Budget Overview Committee said the school budget should be cut "because of deteriorating economic conditions." And at a board meeting earlier this month, Supervisor Joseph Alexander (D-Lee) said the schools should suffer as much as other departments in local government.