The Fairfax County Board of Supervisors voted 6 to 0 Monday to downzone from high-density commercial to residential use a 3.7-acre lot in Great Falls that is surrounded by houses.

The action at least temporarily blocks construction of a proposed office building on a wooded site that contains the remnants of a sawmill.

Traditionally, the downzoning of a single property has been difficult to uphold in Virginia courts.

Broader downzonings, such as the contested but successful board action to restrict development in the Occoquan Basin, a 100-square-mile watershed in western Fairfax, are generally viewed as more justifiable.

In the Great Falls case, county attorneys, in private discussions with the supervisors, had expressed some doubts about whether the courts would uphold the downzoning, according to several county officials.

An attorney for the owners of the property, George and Judy Chang, said his clients will file suit against the board seeking to overturn its action.

At issue is a parcel at Weant Drive and Riverbend Road in Great Falls about two miles north of Georgetown Pike. Since 1978, the property has been zoned C-8, which designates highway commercial zoning, the most intense commercial zoning in the county.

In February, the Changs proposed constructing a three-story office building with about 36,000 square feet of space. It drew opposition from hundreds of Great Falls residents who said that an office building was inappropriate in the middle of their residential community.

In March the county board voted 6 to 1, with Supervisor Thomas M. Davis III (R-Mason) the dissenter, to send the downzoning to public hearings. On June 10, the Fairfax County Planning Commission approved the downzoning.

John F. Cahill, an attorney with the firm of Hazel, Thomas, Fiske, Beckhorn & Hanes who represents the Changs, said at Monday's meeting that the proposed office building is compatible with the community. "There's been no change of circumstances to single out this particular piece of property for downzoning," Cahill said. "They've basically destroyed the value of his property." He added that the Changs will probably seek damages from the board in their suit.

Great Falls residents, who had formed Neighbors for Great Falls, had lobbied hard for the downzoning, retaining the District law firm of Arent, Fox, Kintner, Plotkin & Kahn.

They argued that the earlier commercial zoning was a mistake and that circumstances had changed around the property, including a dramatic increase in traffic.

But one county official, who asked not to be identified, said the Changs are probably "vested," meaning they have the right to develop the property because they filed a final site plan before the county board's action. The downzoning would then apply to any future owners.