WASHINGTON — Sales of existing homes sank unexpectedly last month to the lowest level in nearly 12 years as potential buyers worried about their jobs and awaited details of President Obama's plans to stabilize the housing market.

But the banking industry's teetering fortunes and mounting job losses could stall any recovery. Falling prices and low mortgage rates don't make much of a difference for people who are out of work — or fearful of losing their jobs.

The most optimistic outlook is for a spring revival as home prices plummet. Government officials, hoping to spur demand, yesterday rolled out the details of a new $8,000 tax credit for first-time buyers. About 40 percent of all home sales last year were from first-time buyers.

Treasury Secretary Timothy Geithner said the tax credit should help provide an "immediate response to the current crisis."

The government response may help, but many consumers are still in wait-and-see mode.

"Buyers are sitting back," said real estate agent Sandra Lipmann of Prudential Centennial Realty in Westchester County, N.Y., home to the upscale properties of many Wall Street workers. "They don't have the full story of what's going to happen in this economy."

Sales of existing homes fell 5.3 percent to an annual rate of 4.49 million last month, from 4.74 million in December, the National Association of Realtors said yesterday. It was the weakest showing since July 1997. And some analysts don't see sales bottoming out until later this year as prices sink further. Economists had expected sales to rise to an annual pace of 4.79 million homes.

Without adjusting for seasonal factors, sales nationwide fell 7.6 percent from a year earlier. The West was the only region to show increased sales.

The median price in January fell to $170,300, from $199,800 a year earlier and $175,700 in December. It was the lowest price since March 2003 and the second-largest drop on record.

And the Mortgage Bankers Association said yesterday that applications for new loans and refinances both fell last week as rates inched up.

Sinking home prices and soaring foreclosures have forced major banks like Citigroup Inc. and Bank of America Corp. to record huge losses on the value of their mortgage-related assets.

On Capitol Hill for a second day, Federal Reserve Chairman Ben Bernanke warned lawmakers that the big glut of unsold homes could "put us in real danger" of even sharper declines in home prices.

The Fed chief again spurned speculation that the government may seize control of Citigroup or other large financial institutions.

Asked about Citigroup Inc., Bernanke said nationalization "is when the government seizes the bank and zeros out its shareholders ... we don't plan anything like that."