Fairfax County has ordered 70 school buses with seat belts for use next year in a pilot project that will be the first of its kind in Virginia, school officials said yesterday.

The 64-passenger Ford buses with lap belts will cost $37,000 each, about $1,300 more than buses without belts. The Board of Supervisors appropriated $100,000 for the belts in February, but questions later about whether the buses could be ordered arose because Virginia does not have any installation standards for school bus belts.

County officials said yesterday they had obtained state approval to use a federal standard for the belts. The vehicles, scheduled to arrive in December, will be the first with seat belts used on regular bus routes. Buses for handicapped children in Fairfax already have seat belts.

The county will concentrate the buses in one area, a section that has yet to be selected, said William J. Shadle Jr., an assistant county superintendent. The project will be evaluated after a year.

Betsy M. Boyle of Annandale, director of the Virginia Coalition for Seat Belts in School Buses, which has been pressing the issue, said "I'm thrilled that I'm in this county." She predicted officials will hear demands to install more belts: "Once the parents find out there are 70 buses with seat belts, they'll get a lot of calls."

Under orders from the General Assembly, the state Department of Education is studying whether all school buses should have belts and will report early next year. About 25 school districts in the country require seat belts.

The school bus industry and some federal officials oppose mandated seat belts, contending they are costly and do not improve safety. A parent coalition argues they provide an extra measure of safety and they encourage children to use seat belts in automobiles.