The Fairfax County School Board voted last night to open its future high school for science and technology to students from seven other Northern Virginia jurisdictions.

The vote means the school originally conceived only for Fairfax County will be a state-designated "magnet" institution also serving students from Arlington, Loudoun and Prince William counties and the cities of Alexandria, Falls Church, Manassas and Manassas Park.

But the School Board did not extend the arrangement, which now goes to the other jurisdictions for their approval, beyond the school's first academic year, which will start in the fall of 1985. For it to continue, the contract with the other school districts would have to be renewed before the fall of 1986.

The school, to be called the Thomas Jefferson High School for Science and Technology, will be at today's Jefferson High School in Annandale. In its first year it will have 400 ninth graders and a special one-year program for 200 seniors.

The board's agreement to designate Jefferson as one of four regional magnet schools called for by Gov. Charles S. Robb means that the school will receive $242,000 in state funding in its first two years.

School board members had expressed concern that as a regional school it would not be under Fairfax control. Under the agreement approved last night, the other school districts would play only an advisory role in administering the school.

Fairfax School Superintendent William J. Burkholder made clear that the agreement to be presented to the other jurisdictions was not negotiable and that the superintendents from those school districts would have to sign it if they wish to send students to the school in Fairfax County. He said it was possible that one or two jurisdictions would not go along with the pact.

One worry of the School Board was that some eligible Fairfax students could be denied access to the school. But the regional pact requires that the total number of students accepted from any district not exceed the percentage that the district's school population represents in Northern Virginia.

By today's enrollment figures that would mean Fairfax students would make up at least 64 percent of the science and technology high school students. Burkholder said Prince William students would make up 16 percent; Arlington, 7 percent; Loudoun, 6 percent; Alexandria, 5 percent; Manassas, 1 percent; Manassas Park, .5 percent and Falls Church, .5 percent.

The proposed agreement with the school districts requires that they reimburse the Fairfax school system for the cost of educating their students. David Sawyer, who is coordinating preparations for the school, estimates tuition will cost $4,098 per student.

Each district also would be responsible for its student transportation costs.

School Board Chairman Mary Collier said she would favor including the capital costs of the new school in the per pupil tuition that all jurisdictions would be required to pay. But board member Tony Lane said that if the other seven jurisdictions contributed to the school's capital costs, they might be encouraged to ask for more control in its administration.