The Fairfax County School Board voted last night to inform military personnel at Fort Belvoir whose children attend county schools they will be charged thousands of dollars in tuition unless Congress continues to appropriate money to subsidize their education.

The Defense Department has indicated it will take the School Board to court to halt any attempt at collecting tuition from military families. The Fairfax board's action is believed to be among the first such move in the nation.

The board said letters will be mailed today to the parents of the 1,520 students from the Army base warning that they could receive tuition bills in late October unless Congress provides enough money to cover at least half the cost of educating the children.

The bills would range from $2,600 for an elementary school pupil to $16,330 for a severely retarded youngster in a special education facility.

School Board members said they do not expect the military families will have to pay and that they believe the threat of charging tuition will spur the government to continue its program of impact aid to school districts that serve substantial numbers of students whose parents do not pay local income or real estate taxes because they live and work on federal property.

"We hope this builds a fire under somebody -- quick," said Mason District board member James W. Kitchin.

"Somebody has got to come forward and rescue them," said Board Chairman Ann P. Kahn. "But it is not incumbent on the taxpayers of Fairfax County to pay the $4.4 million cost of educating these children."

In asserting that swift legal action will follow an attempt to collect tuition, Ann Brooks of the Defense Department's office of governmental affairs said following last night's vote, "We guarantee that the parents won't have to pay this tuition."

Every president since Eisenhower has tried -- and failed -- to kill the impact aid program. Congress, under President Reagan's urging, slashed the program almost 37 percent for the next fiscal year. This fall Congress must decide how to divide the remaining $475 million in impact aid among 4,300 school districts nationwide, according to James Maza, lobbyist for an association of impact aid school districts.