If your neighbors have lost their homes, you could pay the price when you try to sell or refinance — even if your credit is good.

Neighbors matter when it comes to putting a price tag on homes. Appraisers use comparable sales data to calculate the value of a home, a number lenders require for selling and refinancing. And comparable sales in neighborhoods plagued by foreclosures knock down the value of homes.

The problem, which makes it much more difficult for borrowers to pull cash out of their homes, is another sign of how a sick housing market infects the entire economy, one neighborhood at a time. If borrowers are unable to refinance at lower rates, that could cause even more foreclosures, mortgage brokers and appraisers say.

"The abundance of foreclosures has turned into a snowball effect," said Karen Mann, a San Francisco Bay area appraiser.

The number of U.S. homes facing foreclosure jumped 57 percent in January from a year earlier, and more than 230,000 homes nationwide received notices from lenders, according to RealtyTrac Inc., based in Irvine, Calif. Nearly 60 percent more U.S. homes faced foreclosure in February than in the same month last year. The highest foreclosure rates have been found in California, Florida and Nevada.

Far-flung suburbs popular with first-time buyers have been hit the hardest by the foreclosure drag. In Northern California, home buyers often stretched to buy homes they couldn't afford by borrowing as much as 100 percent of their home's value, Mann said.

Now, some of those homeowners are walking away from mortgages and turning properties over to their lenders.

Appraisers commonly base their calculations on property sales over the last six months within a half-mile radius of the property. But declining markets make that calculation difficult — especially if there are no recently completed sales and a large number of nearby foreclosed properties on the market.

"It's difficult to get a good assessment of what the valuations would be in this type of market," said Global Insight economist Brian Bethune. "Everybody knows that there's some downward pressure, but how much? This whole appraisal process has become a lot more complicated."

Foreclosure listings don't represent the true value of neighboring properties, because they're often damaged goods, says Loreen Stuhr, a Las Vegas appraiser. "We see cases where, the homeowner, in frustration, has trashed the property before they left," she said.

A better approach, she said is to look at older sales of non-foreclosed properties, and make adjustments to take into account the market's decline — a drop in home values of up to 2 percent every month in Las Vegas.

Rita Bradley, a Southern California appraiser, makes no apologies. Appraisers, she said, are obligated to look at all the properties in the area, including bank-owned properties on the market. "Just because you can pull a sale from five months ago doesn't mean it's really indicative of what's happening in the neighborhood today," she said.

Consumer groups have predicted that the wave of foreclosures would pull down property values and lower property-tax revenue for state and local governments.