The Prince William County School Board, to the consternation of some county officials, has voted to appeal a court ruling directing it to make public its contract with county School Superintendent Richard W. Johnson.

One Prince William supervisor warned yesterday that if the school board persists, it had best be prepared to pay the price.

"This is ridiculous," said Supervisor John D. Jenkins of the Neabsco district. "I think the board is exercising very poor judgment, and I expect to reduce [the board's] budget appropriation by the cost of the appeal."

Board members should be ready to put not only their money where their votes are, but their heads as well, Jenkins said. "I'm going to look very hard at any board members coming up for reappointment. I can't support any member that would willfully vote to waste the taxpayers' money."

After discussing the matter in executive session late Wednesday, a sharply divided school board voted 4 to 3 in open session to contest Circuit Court Judge Percy Thorton's ruling Tuesday that Virginia's Freedom of Information Act applies to Johnson's contract. The Prince William Education Association, a teacher group, had sued the board over its refusal to divulge details of Johnson's contract, which pays him $68,500 a year through 1989.

The group and others have alleged that the board secretly promised Johnson a large severance payment if he is fired before his contract ends. They have demanded that all contract details be made public.

Ilona Salmon, one of those voting for the appeal, said yesterday that she favors a uniform statewide policy about whether school systems must release superintendents' contracts, and that it is unfair to force Prince William to divulge its contract if other systems do not have to.

"We feel that our superintendent should have the same right to privacy as any other superintendent," she said.

Frank E. Barham, executive secretary to the Virginia School Boards Association, said yesterday, however, that only about 25 of Virginia's 135 school superintendents have written contracts with their boards. Most of these have been released to the public, he said.

The school board's attorney, Richmond lawyer Patrick Lacy, said yesterday that Thorton's decision would apply only in Prince William, but that an appeal to a higher court would establish a policy for all of Virginia school systems.

Many Prince William citizens yesterday shared Jenkins' resentment toward the board.

"I think general community feeling is that in a democracy a matter of this kind should be made public," said Kathryn Perrin, a Prince William parent. "I think the community feels that money should be spent on the children, not on lawyers' fees."