A dormant nine-year-old plan to establish a state-sponsored, tuition-free boarding school for Virginia's best high school students has been formally endorsed by the state Board of Education.

The 5 to 3 vote last month represented the first official action favoring the plan, which came from parents and educators and appeared to have some legislative backing when it was introduced. Although no money was authorized and no timetable was set, the move represents a major breakthrough for the proposal.

"Somebody has to step forward and say, 'We're willing and interested in pursuing it,' " board President Suzanne F. Thomas, of Alexandria, said before the vote. "And we're the ones to do that."

While avidly supported by some parents and business leaders, the proposal has been opposed vigorously by local school superintendents and consigned to the limbo of repeated feasibility studies.

"Before we start talking about sleepovers for gifted children, I think we ought to talk about doing some of these special things for regular kids," said Sandra Adair Vaughan, a state school board member who was absent from the recent meeting in Richmond. "People want to do something for the very top children, but we're not doing the basic things for the bottom quartile."

If eventually financed, the school would closely resemble one outlined in an ill-fated 1988 proposal offered by Maryland Gov. William Donald Schaefer. And in many ways, it would be a live-in version of the widely acclaimed, five-year-old Thomas Jefferson High School for Science and Technology in Annandale.

A state Department of Education report to the board outlined tentative plans to admit 600 to 900 gifted students in 10th through 12th grades. Students would be offered accelerated courses in various subjects, particularly math and science, and would be required to perform community service to graduate.

A site has not been selected. The National Trust for Historic Preservation has expressed interest in putting the school at Montpelier, James Madison's 2,677-acre estate in Orange County, 75 miles southwest of Washington.

Because it would be a public school, students would pay no tuition. However, the price for the state represents a formidable obstacle at a time of pessimistic economic forecasts and across-the-board state budget cuts.

According to rough estimates, building a school could cost $20 million to $30 million and annual operating expenses for 900 students could reach $12 million -- money that Gov. L. Douglas Wilder said recently could be hard to find in the current fiscal climate. Officials suggested the start-up costs could be reduced by renovating an existing state building and stressed that private funds must also be tapped.

Despite their cost, such schools have become increasingly popular in the United States in the past decade.

North Carolina, Louisiana, Illinois, Texas, Mississippi and South Carolina have established their own schools since 1980. Oklahoma and Indiana plan to open residential schools this year.

In 1988, Schaefer pushed for a residential math-and-science school in Maryland, but state legislators, wary of creating an elite school that would take money away from cash-strapped schools in Baltimore, balked at the $13.3 million price and rejected the plan.

Similar concerns have sidetracked the Virginia plan since the General Assembly first asked for a study in 1981.

Critics complain that the school would serve only a few of the state's qualified students, that it could divert critical education money from needy areas and that it would rob school districts of their best students.

The disparity in funding between school districts has become an intense issue in Virginia, as a state commission studies ways to equalize opportunities. The poorest school district, Nottoway County in rural Southside, spent $2,610 per student in 1988-89 compared with $6,953 per student in the richest school district, Alexandria, according to a recent study.

By comparison, the Department of Education estimated that the boarding school for the gifted would cost about $13,500 per student per year, including room and board.

Sensitive to the concerns, proponents of the boarding school also cast their arguments in terms of disparity.

Such a school, they contend, would open the door for gifted students in small or poor districts to opportunities they have not had. Jefferson and four half-day magnet schools elsewhere in the state serve students in only 24 of Virginia's 133 school districts, and none is a boarding school.

Advocates believe that living and studying with other bright, highly motivated teenagers would foster an exceptional academic atmosphere unavailable in regular schools.

Jane S. Craig, the education department's associate director for gifted programs, cited the experience of the residential summer Governor's Schools for the Gifted, which have been offered since 1974.

"Students who come from small, rural districts tell us that they realize for the first time that there are others like them," she said.