Clayton County's rate of seriously delinquent mortgages has reached epidemic proportions, with nearly one in 10 mortgage accounts at least 60 days past due, according to data from one of the nation's largest credit reporting companies.

Clayton had the highest delinquency rate for mortgages in an 11-county area of metro Atlanta, according to Chicago-based Trans-Union.

But late payments were up significantly in every metro Atlanta county, even in relatively high-income suburbs such as Forsyth, Fayette and Douglas counties. The share of seriously delinquent mortgages in each of those three counties increased by more than 70 percent between the beginning of 2005 and the end of 2007, according to the data.

The data is based on a survey of 27 million consumer records during the fourth quarter of 2007.

Across metro Atlanta, 4.2 percent of mortgages were at least 60 days past due at the end of last year. That's 40 percent higher than the national average.

"A lot of those folks are going into foreclosure," said Dan Immergluck, a professor at Georgia Tech who is an expert on mortgage lending. "What that means is a lot of those folks are shut off from credit markets for a while. People think of it as a short-term problem, but it's a long-term problem."

Most lenders seek foreclosure if a homeowner falls three payments behind. Once the proceedings begin in Georgia, a house can be sold on the courthouse steps in as few as 37 days.

Foreclosures have reached record levels across metro Atlanta. And every new wave of foreclosed properties hurts values in a real estate market already flooded with houses for sale.

Metro Atlanta posted high rates of delinquent mortgages even though it had not experienced the dramatic run-up in real estate prices that states such as California and Florida experienced. Metro Atlanta also differs from Ohio and Michigan, where the economy has taken a nosedive.

"Atlanta doesn't have any of those characterizations of a super-hot bubble or a super-weak economy, but it's still tracking the national numbers," Immergluck said. "I think that has something to do with the Wild West lending around here."

Georgia ranked sixth nationally for its rate of delinquent mortgages.

Mortgage failures are now extending beyond relatively risky subprime loans to the traditional prime loans, experts said. Because prime loans make up the majority of loans, an uptick in delinquencies in those mortgages has a significant impact on the total number of foreclosures.

Keith Carson, a senior consultant in TransUnion's financial services group, said he expects the national delinquency rate to rise from 3 percent to 4 percent by the end of 2008.

"There is a misconception that this is solely restricted to some subprime loans and hybrid ARMs [adjustable rate mortgages]," Carson said. "It goes beyond that."

Immergluck said the rising rate of foreclosures in an upscale county such as Forsyth suggests the spread of foreclosures into the prime market. In lower-income counties such as Clayton, foreclosures have become so widespread that they are likely to have a devastating impact on housing values in some neighborhoods.

"I'm extremely concerned about it," said Eldrin Bell, chairman of the Clayton County Commission. "I will do everything possible that I can within the county's authority to assist with these issues."

Bell said he is personally concerned about the trendlines because many of the families facing foreclosure in Clayton County are single mothers with children. Bell said thousands of these families moved to Clayton in recent years with their eyes on the prize of homeownership.

"I am just beside myself," he said. "To me it's a moral issue and a moral obligation to protect families, to keep them together. If they get kicked out of housing, what are they going to do?"

Delinquency rates are high in Clayton, even though the county's residents have the lowest mortgage balances in the region. The average Clayton mortgage was $137,000, compared with the region's highest in Fulton County at $271,000.

The average amount owed on mortgages has taken a hit with the foreclosure crisis, the TransUnion data indicated. Across metro Atlanta, the average amount owed on a home loan declined between the third and fourth quarters of last year, from $208,000 to $193,000.

TransUnion's Carson said he believed the decline was a result of lower home prices driven by the oversupply in the market. But Georgia Tech's Immergluck said he thought the number was driven by the earlier failure of many higher-priced mortgages.

"I think it's the big loans being pulled out because they have gone into foreclosure," he said.