The Fairfax County Board of Supervisiors said yesterday county school authorities "blew it" when they voted last month to save 103,000 gallons of gasoline by reducing bus service to some students next year.

Reacting to angry complaints from parents, the election-minded supervisors voted unanimously to ask the school board to reconsider its decision.

Acting school superintendent William J. Burkholder said yesterday the school board was forced to take action because of cuts that the supervisors made in the school budget and because the county has told the schools to cut back on gasoline consumption.

"We did not have any place to cut without affecting people," Burkholder said.

Before the school board acted on May 24, students living more than 1 1/2 miles from their school could take a bus. Starting next fall, however, intermediate school students must live two miles or more from their school to ride a bus. High school students must live 2 1/2 miles from their school.

Burkholder said the school board increased the walking radius because that was the only way it could deal with the $1.4 million cut the supervisors made in the school board's proposed "lean" budget for fiscal year 1980.

But yesterday the supervisors, six of whom are running for reelection this fall, expressed no interest in the school board's budget problems.

Supervisor Marie B. Travesky (R-Springfield), the only member of the board who faces a challenge in today's primary election, introduced a resolution saying that the increased walking distance will "impose a hardship" on students and their parents.

"More parents and students will be driving cars to the schools using vastly more gasoline than that which the school system will save," Travesky said. "In short, the school board blew it."

The school board estimates that cuts in bus service, besides saving 103,000 gallons of gasoline, will save $390,000 and cut 3 bus drivers' positions.

Burkholder said that while some parents have expressed anger at the decision, others have called the school board to say that they think their children should do more walking.

In addition, Burkholder said that the county staff has recently informed the schools that they are to come up with some method of saving 10 percent of their projected gasoline consumption. Burkholder said the reduced bus service will do just that.

Students who cannot walk "safely" to school - those who must cross a major highway or other dangerous obstacle - will continue to be bused even if they live inside the new boundaries for walking.

Burkholder said yesterday the county school board will follow the supervisors' directions and take another look at its new policy.But, he added, "that doesn't mean the board is going to change its decision."

The Board of Supervisors determines the amount of money the school board receives from county taxpayers, but the supervisors do not have authority to order the school board to spend its money in any particular manner.