“You don’t mind making a $2,000 payment when the house is going up” in value, said Steve Walsh, a mortgage broker in Scottsdale, Arizona, who has seen several clients walk away from their homes because they couldn’t refinance or sell. “When it’s going down, it becomes a weight around your neck, it becomes an anchor.”

Home prices in the North Las Vegas neighborhood of Brenda Harris, a technology analyst at a casino company, have fallen 20 percent to 30 percent. The builder who sold her a new three-bedroom home on Pink Flamingos Place for about $392,000 in 2006 is now listing similar properties for $314,000. A larger house a block down from Ms. Harris was recently listed online for $310,000.

But Ms. Harris does not want to leave her home. She estimates that she has spent close to $40,000 on her property, about half for a down payment and much of the rest on a deck and landscaping.

“I’m not behind in my payments, but I’m trying to prevent getting behind,” Ms. Harris said. “I don’t want to ruin my credit.”

In addition to the declining value of her home, Ms. Harris, 53, will soon be hit with a sharply higher house payment. She has an option adjustable-rate mortgage, a loan that allows borrowers to pay less than the interest and principal due every month. The unpaid interest gets added to the principal balance. She is making the minimum monthly payments due on her loan, about $2,400.

But she knows she will not be able to pay the $3,400 needed to cover her interest and principal, which she will be required to pay once her loan balance reaches 115 percent of her starting balance. And under the terms of her loan, which was made by Countrywide Financial, she would have to pay a prepayment penalty of about $40,000 if she chose to refinance or sell her home before May 2009.

She said that she now wishes she had taken a traditional fixed-rate loan when she bought the home. At the time, she asked for a loan that could be refinanced after one year without penalty. She said her broker had told her a week before the closing that the penalty would extend until May 2009 and that she reluctantly agreed because she had already started moving.