Fairfax County's controversial system of appealing real estate has been upheld by the Virginia Supreme Court in a ruling that county officials said may reduce the flow of assessment protests there.

Although the court decision applied to one disputed assessment on commercial land near Tysons Corner, the court appeared to have gone much further in its unanimous ruling.

"The evidence is undisputed that the county's apprasial-assessment technique was lawful," said Justice A. Christian Compton, referring to a procedure that has provoked many property tax disputes in the county.

Under the Fairfax system, recent land sales are used to help gauge the value of nearby property. But because the county uses a number of other factors -- topography, zoning and access -- the assessments on parcels in the same area can vary.

The court rejected arguments that the assessments for all land similarly situated must be equal. "Uniform operation of the law does not mandate uniformity or results," Compton said.

A top Fairfax official, who declined to be identified, called the ruling "real significant" yesterday and predicted that it would deter a number of people from contesting assessments in the county. "The decision give the seal of approval to the county's system of assessment. "That's real nice to have," he said.

In the past, the Virginia Supreme Court has endorsed assessment techniques similar to those used by Fairfax, but it had never specifically approved the county's system.

The immediate issue in the case was assessments by Fairfax in the mid-1970s that valued an 84-acre parcel at almost $90,000 an acre. Leasco Realty Inc., the owner, contended the assessment was too high, and in 1978, Fairfax Circuit Court Judge Burch Millsap agreed, putting the value at slightly more than $50,000 an acre. The county appealed.

Leasco Realty, whose parent computer company hoped to build a large coroporate headquarters on the site, later sold the land after encoutering financial difficulties. Most of the land was sold in the late 1970s at prices that topped $175,000 to $200,000 an acre.

The Leasco tract, whcih originally included 98 acres, is the site of one of the biggest commercial office projects in the Washington area.