The task of determining the taxable value of homes and land in Loudoun rests largely on the shoulders of nine county government appraisers who are responsible for a total of 42,000 properties, staff members told the Board of Supervisors this week.

Properties considered relatively routine, such as tract houses, are evaluated by appraisers who each must monitor as many as 8,000 separate parcels and determine their values each year.

The heavy workload was described to the supervisors Monday in a briefing about the assessment process. The supervisors are regularly under pressure from constituents unhappy about their assessments, the tax rate or their tax bills.

The county government's goal for actual inspections of properties by county appraisers is that each parcel be visited at least once every four years, appraiser Tammi Loving said. For properties in transitional areas, or those having large lots or other special conditions, officials attempt to visit the sites more frequently, appraisers said.

But regardless of how often the appraisers hit the streets, their guiding principle in determining assessments is how much someone would pay for the property. For some parcels, the "highest and best" potential use must be factored in along with recent sales information, appraisers said.

"Everything we do comes back to the market," said appraiser Nancy Dolinger, who evaluates large parcels and those that are difficult to set a value for. "The appraiser doesn't set the value," she said, "the market sets the value -- the buyers and the sellers."

County Assessor William Gardner noted that his office is bound by state laws, court decisions and the standards of a professional association as to how it determines the worth of houses and land. He acknowledged that the real estate market has declined rapidly in Loudoun this year, but he said he could not predict how assessments will change from this year to next.

"I don't know that any of us knows for sure," said Gardner. "We are very actively seeking information from people out there in the marketplace."

Assistant Assessor Bob Willingham said the downturn in the real estate market "may last another two years."

For purposes of developing a budget proposal for the fiscal year that begins next July, the county administration is estimating that the total tax base (the combined assessed value of all properties in Loudoun) will stay level or decline as much as 5 percent next year.

After several years of rapid increases in the tax base, that would mean a decline in real estate taxes if the tax rate remains at 85 cents per $100 of assessed value, officials say. Because of the sour market, they note, some property owners will have trouble finding buyers at anywhere near the assessed values of their parcels.

Nevertheless, staff officials told the supervisors Monday, assessments must take into account the prices of the sales that do happen, even if transactions are few and far between.

"I can assure you we won't go back a year or two" in an attempt to use earlier sales to help determine today's property values, Gardner said, recognizing that in the late 1980s, speculation drove some prices far beyond what the parcels should be valued at today.

Assessment officials said they normally do not consider the prices paid for auctioned properties when computing new assessments of comparable or nearby parcels because auction sales are viewed more as forced transactions than as "arm's length" sales that reflect open market values.

Residents who do not agree with the assessments of their properties can ask for explanations and reconsideration by the appraiser, can appeal to the county Board of Equalization, and can file suit in Circuit Court.

The assessments office has "an open-door policy," Loving said. "We'll meet with the taxpayers throughout the year."