In Las Vegas, Ken Lowman, a longtime agent for luxury properties, said four of the 11 sales he brokered in June were distressed properties.

Image A home in foreclosure in Los Altos, Calif., a city where the median home price is $1.5 million. Credit... Peter DaSilva for The New York Times

“I’ve never seen the wealthy hit like this before,” Mr. Lowman said. “They made their plans based on the best of all possible scenarios  that their incomes would continue to grow, that real estate would never drop. Not many had a plan B.”

The defaulting owners, he said, often remain as long as they can. “They’re in denial,” he said.

Here in Los Altos, where the median home price of $1.5 million makes it one of the most exclusive towns in the country, several houses scheduled for auction were still occupied this week. The people who answered the door were reluctant to explain their circumstances in any detail.

At one house, where the lender was owed $1.3 million, there was a couch out front wrapped in plastic. A woman said she and her husband had lost their jobs and were moving in with relatives. At another house, the family said they were renters. A third family, whose mortgage is $1.6 million, said they would be moving this weekend.

At a vacant house with a pool, where the lender was seeking $1.27 million, a raft and a water gun lay abandoned on the entryway floor.

Lenders are fearful that many of the 11 million or so homeowners who owe more than their house is worth will walk away from them, especially if the real estate market begins to weaken again. The so-called strategic defaults have become a matter of intense debate in recent months.