Prince William County Circuit Judge Percy Thornton has rebuffed an attempt by the county school system to keep secret the terms of its employment contract with Superintendent Richard Johnson.

At a hearing Friday, Thornton rejected a School Board request that a lawsuit over the contract filed by the Prince William County Education Association, a teachers group, be thrown out of court. Thornton ruled that Johnson's contract may be an official document and subject to disclosure under the Virginia Freedom of Information Act.

He said that question will be resolved at a Feb. 12 trial.

When the county School Board renewed Johnson's employment contract for four years in January 1985, it gave him a $9,000-a-year raise and a "buy-out" clause that Johnson had requested in case he is removed before his term expires.

Since then, the board has been under pressure from parent groups and local newspapers to reveal the details of the contract, which became effective July 1. The board has denied all requests, including one by the 1,500-member teachers association in June, arguing that the contract is a personnel matter and may be kept private.

Cameron Yow, director of the teachers group, noted that Thornton's decision followed an opinion issued by Gov.-elect Gerald L. Baliles while serving as state attorney general. In his opinion, which is advisory and does not carry the weight of a court ruling, Baliles said that the board was not required to reveal the contract details but that there was nothing in state law that "prevents the School Board from disclosing the contract if it chooses to do so."

In a 5-to-2 vote the School Board approved a resolution accepting Baliles' opinion.

Several school officials said privately that they would support a move to ask the board to reconsider its decision at its meeting Wednesday. "We may be asked to reveal the contract anyway -- we may as well save the money attorney fees and court costs ," one official said.

"This whole thing has gotten out of hand," said Brentsville School Board member George Mullen. "The people are paying the superintendent's salary; they should know what's in that contract."

The contract, which pays Johnson $68,000 annually, allows the board to terminate Johnson's employment without cause at any time during the next four years.

Yow said the teachers have vowed to take the issue to the state Supreme Court if necessary.

The School Board lawyer, Patrick Lacy, a former assistant state attorney general, said, "We have every confidence our case is meritorious, and it will prevail."