A Fairfax County Circuit Court judge overturned the county's law restricting office development on thousands of acres of land yesterday, saying the law was improperly drafted and too vague to pass legal muster.

The ruling was a major victory for landowners, who viewed the 10-month-old law as an attack on their property rights, and a bruising defeat for the county, whose slow-growth leaders said it was needed to crack down on development and improve the county's congested road system.

Board of Supervisors Chairman Audrey Moore championed the law, which was unanimously passed in a chaotic board meeting in December. It was one of the region's most ambitious attempts to put the brakes on development. It was challenged by hundreds of lawsuits, and was partly reversed last winter by Virginia's General Assembly.

Ruling immediately after closing arguments in a six-day civil trial, Circuit Judge William G. Plummer ruled that the Board of Supervisors violated landowners' rights of due process because it did not follow procedures mandated by Virginia law when it enacted the ordinance restricting development on more than 14,000 acres.

Under old zoning laws, huge office buildings could be built without board approval or public hearings on many parcels that were zoned for industrial uses, stretching from Tysons Corner to Merrifield to the Route 28 and Dulles corridors.

The new ordinance reduced by as much as half the amount of development allowed on most commercial and industrial land and prohibited office construction, except by special permit, on many commercial and industrial parcels.

Attorneys for landowners argued during the trial that the law passed Dec. 11 was vague, riddled with mistakes and adopted amid a whirl of confusion.

The actual text of the zoning law was not drafted until a week after the board passed the law, according to testimony. When the written text was presented to the board, it contained several clerical errors and had to be revised.

Landowners called the decision a major victory yesterday, but tempered their comments, noting that the county could pass another ordinance or appeal the ruling.

"I'm very pleased to see the results and I'm really relieved this turmoil we suffered through in the last year now has an opportunity to end," said C. Thomas Hicks III, the president of the Northern Virginia Chapter of the National Association of Industrial and Office Parks.

"What we would like to see is some consensus of leadership on the Board of Supervisors starting next Monday to say, 'Let's stop the hemorrhaging, stop throwing money in this ill-conceived battle and let's see whether we can work with the business community and the citizens to solve our problems."

L. Burwell Gunn, chairman of the Fairfax County Chamber of Commerce, said the ruling was "an opportunity for the board to stop being so divisive and to erase any perception that Fairfax County is anti-business."

Most members of the Board of Supervisors said they were surprised and disappointed by the ruling. Moore was out of town and not available for comment, but a spokesman for her said she "supports strongly and unequivocally the unanimous action the board took in December . . . . If the county attorney and outside counsel recommend appeal, Audrey will support that strongly."

Vice Chairman Martha V. Pennino (D-Centreville) said, "At this juncture, I'm willing to support an appeal because . . . the board had a right to do what it did. I have no regrets."

In his ruling from the bench, Plummer said he found that the board adopted the ordinance in concept and left to its staff to figure out what the board wanted done. The judge said the supervisors should have had a full text in front of them when they adopted the ordinance, making it clear what they were doing.

"The staff during the recess tried to put together a package . . . it believed was what the board had put together in concept," Plummer said. "I don't understand why the board couldn't have waited a week for staff to bring it back."

In addition, Plummer found that the board failed to state a valid public purpose for its actions, as required by state law when government acts to change zoning laws. The judge said the county's statement that the zoning ordinance was necessary to "effectively plan" was not enough.

"Unfortunately, 'to effectively plan,' I don't think that tells the public anything," Plummer said. "The real purpose was to gain control of where office buildings will exist."

"We ask the board to go back and do this thing right if they can do it at all," said Paul Skelly, a lawyer on a committee of attorneys representing landowners. "The law is not satisfied when the board adopts something in concept . . . and leaves it to staff to fill in the gaps. The law is not satisfied when the public is left to guess what exactly it is the board did."

The county, which spent hundreds of thousands of dollars hiring a Richmond-based law firm to represent it, argued that the board may have made mistakes in adopting the ordinance, but that was not reason enough to overturn the law. The intentions of the board, they argued, were clear.

"There can be no doubt cast that thousands knew what was going on," said Everette G. Allen Jr., an attorney for the county. "They may not have known exactly what paragraphs, but they knew what was going on."

The order, which affects about 200 cases, will go into effect Monday when the judge enters a final written order. The county has 30 days to decide whether it will appeal to the state Supreme Court.

Developers said that, because of the region's economic slowdown and the county's slumping real estate market, they did not expect Plummer's ruling to have an immediate effect on the pace of office development.

"The market and the economy are correcting the problems that are perceived with the county's growth, and that's not going to change for the foreseeable future," Hicks said.

He added that the zoning ordinance had exacerbated problems for local developers by reducing the value of their land and making it harder for them to get building loans.

Supervisor Thomas M. Davis III (R-Mason), who is considering running against Moore for the chairmanship next year, said he was not surprised by the decision.

Even though the final board vote was unanimous, Davis said, the reduction in zoning density "was done precipitously" and "had ramifications some of us were not happy about . . . . I think the board in retrospect would have done it a little differently with more of a dialogue with the business community rather than popping it at the last hour."

At the urging of Moore, the board adopted the ordinance before the start of the General Assembly session because of concern that developers would win legislation prohibiting development restrictions.