Fairfax County prosecutor Robert F. Horan Jr. said yesterday he will sue the county's nine supervisors, charging that they violated Virginia's open-meeting law by gathering secretly last December to redraw their election districts.

Horan said the lawsuit, which will be filed in Fairfax Circuit Court Friday, will seek an order prohibiting the board from repeating the episode. "I'm satisfied that the evidence will show that there has been a violation of the law," he said in an interview. "We intend to prove what we allege."

Under Virginia's Freedom of Information Act, county boards and city councils are forbidden to meet in private except in specified cases. Violations of the law are regarded as civil offenses and officials who are found in violation may be punished with personal fines of between $25 and $500, if a judge finds that the violations were willful.

"If the court were to find on the evidence that it was willful, then it could impose a fine," Horan said. "With some supervisors it might be willful, with some it might not."

Several Fairfax citizens groups, including Common Cause and the influential Federation of Citizens' Associations, had requested that Horan file the suit. They argued that board members violated the law when they met without public announcement in Supervisor Audrey Moore's office Dec. 11 to devise a compromise redistricting plan that preserved the seats of all board incumbents. That compromise, which the supervisors toasted with champagne, was ratified unanimously with only minor changes at the board's next public session.

Board Chairman John F. Herrity declined to comment on Horan's decision to file the suit, as did Supervisor Nancy K. Falck, who had earlier defended the board's actions. "If somebody was talking about bringing a lawsuit against you, you wouldn't want to talk about it either," Falck said.

"There's no question that we weren't wise in having that meeting," Moore said. "I think I'll just wait and see what happens."

Prosecutors rarely file suits under the Virginia law and Horan said that his suit will be the first of its type to be filed in the county. The action will place Horan, a Democrat, in the awkward position of suing many of his close political allies who are members of the Fairfax Board.

"It's not something I particularly care to be doing," Horan said in Richmond where he was lobbying the state legislature for stricter laws on criminal sentencing. "The personal end of it bothers me--most of these supervisors are friends of mine."

Horan, who has been mentioned as a potential U.S. Senate candidate this year, said his political plans did not affect his decision to sue the board members. "I think your role as a public official is to carry out the law," he said.

Barbara Pratt, state vice chairman of Common Cause and a Fairfax resident, applauded Horan's decision to sue, saying that county supervisors had failed to provide advance notice of their meeting and had not recorded minutes of the session. "You can't ignore FOI the Freedom of Information law because you don't want to embarrass people," she said. "You cannot use the law when it suits your purpose and ignore it when it doesn't."

The Fairfax board frequently cites provisions in the law when it goes behind closed doors to discuss litigation, personnel, or real estate transactions. Under the act, those are subjects that can be used as justification for a private session.

Under terms of the Virginia law, the Horan lawsuit is supposed to be heard within seven days of being filed. Any fines assessed public officials under the act are to be paid into the State Literary Fund, which supports schools and public libraries.

At least one Fairfax supervisor, however, has said he believed the board was justified in keeping its redistricting meeting a secret. "We just felt that we had to talk it over," Supervisor Joseph Alexander said at the time. "It's been done before, and it'll be done again.''