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The smaller, 10-city index, fell 17.7 percent, the biggest decline in 21 years.

“The downturn in residential real estate prices continued with very few bright spots in the data,” said survey lead researcher David M. Blitzer in a statement.

Some analysts said plunging home values may produce new activity in the depressed residential real estate market. The Commerce Department and the National Association of Realtors both have reported that home-sale activity picked up in September.

The White House Tuesday confirmed it was considering new government help for the beleaguered auto industry, which has hurt by the declining general economy and by a credit crunch that has slammed both dealers and potential customers alike. Congress earlier this month approved a $25 billion taxpayer-funded loan program to U.S. automakers for plant modernization alongside the $700 billion Wall Street rescue package.

White House spokeswoman Dana Perino said the administration is working “as quickly as possible” to implement the car industry loan. She said the giant finance arms of General Motors, Ford and Chrysler may also be eligible for aid under the $700 billion Treasury Department program.

“So the automakers have been in contact with us,” Mrs. Perino said, “and we’re trying to work with the tools that Congress has provided us.”

But the government’s wide-ranging efforts to prop up the nation’s banks and credit markets is not cost-free, Anthony Ryan, acting Treasury undersecretary for domestic finance, acknowledged Tuesday.

The current forecast of a record $482 billion for the fiscal year that began October 1 will have to be revised upward in the face of the massive rescue packages and loan programs now in the works, he said.

“This year’s financing needs will be unprecedented,” Mr. Ryan said in remarks to the annual meeting of the Securities Industry and Financial Markets Association in New York.

He added, “The potential for deterioration in economic conditions given the contraction in credit may also affect budget conditions this year.”