However, assessors point out that a stumbling real estate market may not translate to lower property taxes.

Appeals are already up sharply in Maryland, officials said. Assessments were sent Dec. 31 to Maryland homeowners whose properties were up for reevaluation. They have until Friday to appeal for this year. Most Virginia cities and counties and the District will mail their notices by March 1, and they generally give homeowners 30 to 45 days to appeal.

Some of the most headline-grabbing real estate trends, such as the soaring foreclosure rate, only indirectly affect assessments. Assessors usually review home sales records neighborhood by neighborhood and examine pricing patterns to update individual home values. They disregard homes that were foreclosed on, sold at fire sale or otherwise traded hands under what is considered to be duress.

But such transactions tend to pull down values of sales around them, and that shows up. Assessors say they are well aware that real estate prices have been falling and have built that into their latest valuations. For instance, in Fairfax County, officials estimate that assessments for the 340,000 homes on the tax rolls will decline by 10 to 14 percent this year. In the Sterling district of once-booming Loudoun County, the value of existing homes dropped an average of 31.1 percent. There, the trend is so disturbing to homeowners that some who are trying to sell have been calling the county assessor's office, complaining their valuations are too low.

However, it's much more common for homeowners to argue that the values are inflated.

Appeals of current assessments are rising, and they tend to flow in greater numbers as the deadline approaches, said John Brennan, supervisor of the Montgomery County office of the Maryland Department of Assessments and Taxation. The parts of Montgomery County that just received assessments saw valuations go down 16 percent, the steepest drop in the state.

In previous years, about 5 percent of homeowners who appealed saw some reduction in their assessment. Now, "a pretty fair number of those will get market adjustments because the market has come down," Brennan said. "But what a lot of people won't understand is that even with the reduction in their values, it might not have any effect on their tax bills."

That's because assessments are only part of the tax equation. Another part is the tax rate used to calculate the total due. Budget-strapped governments are still grappling with where to set rates for tax bills when they send them out this summer.

Assessment caps are another reason tax bills might not drop as much as property values have. The District and many Maryland jurisdictions cap assessments to varying degrees; Virginia does not. The caps serve to spread out over several years the higher assessments that occur during periods of rapid real estate price inflation. That prevents dramatic upswings in tax bills in any one year but also dampens the effect of lower valuations.

Cindy Smith-Page, director of real estate assessments for Alexandria, will mail new assessment notices to about 45,000 homeowners in mid-February and is expecting a higher volume of appeals.

"People will be anticipating a greater decline in the value of their homes than we've seen already," she said. "Just with the financial constraints on so many people these days, I think everybody's paying closer attention to all their financial issues. And certainly how much they are paying in property taxes and their ability to do that is at the top of their list."

Assessors say there are several ingredients for a successful appeal:

· Arm yourself with information on fair-market comparisons by looking at sales only within the calendar year of the assessment. Sales that have taken place since then generally don't count.

· If relevant, provide evidence that the assessment office has incorrect information about your property, such as too many square feet or too many rooms.

· Show extenuating circumstances that might detract from your property's value, such as a cracked foundation, a leaky roof, fire damage or other flaws that could result in a reassessment.

"Things that won't work," said Richie McKeithen, director of real property tax administration for the District, "would be like 'My wife and I are splitting up, and I can't afford it.' Or 'I only paid $30,000 for this house in 1960. It can't be worth $300,000.' I'm very sorry, and I sympathize with you, but that's not a valid reason for a reassessment."

In the District and much of Virginia, assessments are annual and so are appeal deadlines. In Maryland, properties are assessed every three years. There, homeowners can appeal the new assessment within 45 days. If they got their reassessment in a previous year and think they have new information that could change the value of the property, they can appeal by filing a "petition for review." So-called off-cycle petitioners have until Jan. 1 to ask for a review of a current assessment.

Watching the sales prices of homes in his Silver Spring neighborhood decline last year, Kenneth Cohen decided to do just that. Last year, the Montgomery County tax assessor valued Cohen's 44-year-old home at $361,347, a 10 percent increase from his previous assessment, which set it at $328,498. He said he didn't think that reflected what has been happening in the real estate market.

"Our assessments are very high compared to real property values," said Cohen, a retired Federal Aviation Administration engineer. "The home prices are really upsetting. The last sale, which is two doors down from us, sold for $347,000 about a month ago. Others are sitting empty. It's deader than a doornail. Nothing's moving."

He hoped to persuade the state to roll back his assessment based on more recent sales prices. He is not alone. Montgomery County's off-cycle petitions for review have hit record numbers. They rose to 3,500 for 2009 assessments from about 1,200 for last year's. There were only 85 petitions for review of 2007 assessments, according to Brennan, of the Maryland assessment department. The three-person appeals board is working its way through petitions and appeals, more than a dozen a day, according to its chairman, Arnold Gordon.

Gordon recommends that homeowners review all the rules for appealing on the state and county Web sites and request what is known in Maryland as a "computer-assisted mass appraisal worksheet" on sales of comparable properties to argue their property value has declined. Those sheets can be provided for a small copying fee by the assessor's office and will list details about the condition and upgrade of comparable properties, such as swimming pools, tennis court, sheds and other structures that might help you make the case your home is worth less.

He also notes that assessors look only at sales of properties within the year the assessment is done, so that even if newer sales show much lower prices, they would not necessarily be considered.

Key among all the recommendations is that homeowners pay close attention to the deadlines for filing appeals or reviews of their assessments. There is very little room under the statute to consider late appeals, Gordon said, and being busy or out of the country won't work.

Cohen found this out the hard way.

Last week, he received an e-mail from the state assessment office acknowledging his petition for a review of his earlier-year assessment. He had missed the deadline, the e-mail said. He thought he would appeal the 2009 value placed on his home when it was reassessed last year. But that deadline, which was the beginning of January, has passed. He still has one more opportunity. He has until Dec. 31 to ask the state to review the 2010 value noted on that assessment from last year. Cohen said he plans to do that.

"With our economy in such a state of shambles, it is necessary for us to avoid the overpayment of taxes," he wrote back to the state assessor's office.