In Buffalo, where officials said the problem had reached “epidemic” proportions in recent months, the city sued 37 banks last year, claiming they were responsible for the deterioration of at least 57 abandoned homes; the city chose a sampling of houses to include in the lawsuit, even though the banks had walked away from many more foreclosures. So far, five banks have settled.

In Kansas City, Rachel Foley, a lawyer who handles housing cases, said bank walkaways were “a rare occurrence two to three years ago.”

“We’re seeing them dumped more and more at the moment,” she said.

Experts suggest the bank walkaways are most visible in states where foreclosures are processed through the courts and therefore tend to be more transparent. Other states, like Indiana and New York, have court-mandated foreclosures, but roughly half of the states allow foreclosures to proceed without court intervention, making it difficult to accurately count the number of bank walkaways in recent months.

Image After Ms. James had her tenants move out, vandals hit the home. It is set for demolition, but the title is still in her name. Credit... Sally Ryan for The New York Times

The soft housing market and the vandalism that often occurs when a house sits empty are the two main factors influencing the mortgage holders’ decisions to walk away, said Larry Rothenberg, a lawyer for Weltman, Weinberg & Reis, one of the larger creditors’ rights firms in the country.

“Oftentimes when the foreclosure starts out, it’s a viable property,” Mr. Rothenberg said, “but by the time it gets to a sheriff’s sale, it might not have enough value to justify further expense. We’ve always had cases where property was vandalized or lost value, but they were rare compared to these times.”

The problem seems most acute at the bottom of the market  houses that were inexpensive to begin with  and with investment properties, where investors and banks want speedy closure by writing off bad loans as losses. Banks and investors typically lose 40 percent to 50 percent of their investment on every foreclosure.