Coruscation

The lenders' thinking, said the economist Thomas Lawler, went like this: "I lend someone $200,000 to buy a house. Then he says, 'Look, I have someone willing to pay $150,000 for it; otherwise I think I'm going to default.' Do I really believe the borrower can't pay it back? And is $150,000 a reasonable offer for the property?"

Short sales are "tailor-made for fraud," said Mr. Lawler, a former executive at the mortgage finance company Fannie Mae.

Last year, short sales started to increase, although they remain relatively uncommon. Fannie Mae said preforeclosure deals on loans in its portfolio more than tripled in 2009, to 36,968. But real estate agents say many lenders still seem to disapprove of short sales.

Under the new federal program, a lender will use real estate agents to determine the value of a home and thus the minimum to accept. This figure will not be shared with the owner, but if an offer comes in that is equal to or higher than this amount, the lender must take it.

Mr. Paul, the Phoenix agent, was skeptical. "In a perfect world, this would work," he said. "But because estimates of value are inherently subjective, it won't. The banks don't want to sell at a discount."

There are myriad other potential conflicts over short sales that may not be solved by the program, which was announced on Nov. 30 but whose details are still being fine-tuned. Many would-be short sellers have second and even third mortgages on their houses. Banks that own these loans are in a position to block any sale unless they get a piece of the deal.

"You have one loan, it's no sweat to get a short sale," said Howard Chase, a Miami Beach real estate agent who says he does around 20 short sales a month. "But the second mortgage often is the obstacle."

Major lenders seem to be taking a cautious approach to the new initiative. In many cases, big banks do not actually own the mortgages; they simply administer them and collect payments. J. K. Huey, a Wells Fargo vice president, said a short sale, like a loan modification, would have to meet the requirements of the investor who owns the loan.

"This is not an opportunity for the customer to just walk away," Ms. Huey said. "If someone doesn't come to us saying, 'I've done everything I can, I used all my savings, I borrowed money and, by the way, I'm losing my job and moving to another city, and have all the documentation,' we're not going to do a short sale."