Fairfax County School Superintendent Robert R. Spillane yesterday proposed a $589.2 million operating budget for county schools next year, a 7.1 percent spending increase that would provide 4 percent raises for all school employes, an amount that has been denounced by the county's teacher associations.

In his first budget, Spillane, who has been on the job since July 1, would increase funds for schools by $39 million in 1986-87, and raise the county's contribution by 7.95 percent.

Spillane said he believes the spending plan will be acceptable to the Board of Supervisors. "I will be disappointed" if they prune it, he said.

Most of the budget growth, $26.4 million, would pay for increases in employe salaries and benefits. The two teacher associations are staging a "work-to-the-rule" slowdown to protest the 4 percent cost-of-living increase.

Spillane's salary proposal also increases the teacher starting salary, now $18,385, to $20,000, and provides more money for the system's most senior teachers; overall, teacher salaries average $29,000. The teacher associations contend that two-thirds of the system's teachers will get nothing beyond the cost-of-living raise and their normal grade increases.

Spillane said he will not reopen salary discussions with teachers, who are prohibited from striking under Virginia law. If the School Board decides to grant them more money, Spillane said he would oppose taking the funds from other programs.

"I'm certainly not against any increases that teachers might get, but I have to balance the needs of instructional programs in the budget," he said.

Rick Nelson, president of the Fairfax County Federation of Teachers, the smaller of the two teacher associations, told the county Board of Supervisors yesterday that the county schools are "bloated with bureaucracy," and that administrators are getting salary hikes of 6.5 percent to 20 percent this year on top of their cost-of-living hikes, while teachers get only 4 percent.

Spillane, whose office is preparing a detailed reply to Nelson's charges, declined immediate comment.

The budget projects that new housing and a baby boomlet will add nearly 2,700 students to the area's largest school system next year. The budget proposes adding 109.4 new jobs and spending $2.2 million on 50 new buses, drivers and attendants to accommodate that growth.

Spillane attached to the budget a $6.6 million wish list of "unfunded requirements" he would ask the supervisors to approve should additional money be available. Included are a more sophisticated central computer, $1.1 million in capital improvements and $3.4 million to replace aging trucks and buses.

Spillane released his proposed school budget to the 10-member School Board last night. The board holds hearings Feb. 3 and 4, and is scheduled to vote on the proposal Feb. 19. It then goes to the supervisors for final approval.

The budget also would require a 10-cent increase in the price of school breakfasts and lunches, the first increase since 1981-82. Lunches currently cost 75 cents for elementary school students and 85 cents for high school students.

The other major spending item in the budget is computers and the people to run them. The budget asks for $2.9 million for improved computer instruction.

"In general, what this represents is moving away from teaching about the computer . . . to teaching the uses of the computer across the curriculum," said Mary Anne Lecos, assistant superintendent for instruction.

The money would pay for the first year of a three-year project to use computers to help teach writing, problem-solving and science. Use of computers would be expanded for business and special education students as well.

In elementary schools, for example, the aim is to have one microcomputer for every 75 students. The current ratio is one to 120. Lecos said school systems on the "cutting edge" of computer technology have one for every 25 students. The new effort, she said, would put Fairfax "just about in the mainstream."

Other major items in the budget include $328,240 to reduce kindergarten class size by hiring new teachers so there will be no more than 28 students in a classroom for each aide and teacher. The current maximum is 30. The board has lowered elementary school class sizes over the past several years, and parents have complained about large kindergarten classes.

Spillane said the combination of parental pressure to reduce class size and the rapid growth of county housing may prompt him to take a second look at speeding up school construction. The superintendent recently proposed construction of seven new elementary schools and an intermediate school over the next five years, but he said the county must consider even more than that.

"Class size is an extremely important issue to the parents," he said. "Had the classroom space been available, I would have looked at reducing class size at the intermediate and elementary levels."

The budget also would add more art instruction in elementary schools, with the aim of providing 16 hours per classroom per year in 1986-87 and an hour a week per classroom within four years. Spillane also asked for more elementary and intermediate school guidance counselors, expansion of the Head Start program to include 125 more preschool students and $292,345 to create a staff training office.

The budget includes no dollar increase in funds allotted to improving achievement of minority students, an official priority of the School Board. But the budget does propose $750,000 for intermediate and high schools with "special needs" -- schools with high turnover and low minority test scores. CAPTION: Picture, Robert R. Spillane . . . proposes $589.2 million budgett. ; Picture /two: chart