Some Republican lawmakers have already objected, saying the effort would amount to throwing good money after bad. But the White House on Wednesday left the door open to a legislative compromise with Congress.

“I know the automakers are important to the United States,” Mr. Paulson said. “We care about the automobile industry.” But he cautioned that “my focus is on the financial sector  getting credit going, getting lending going.”

White House and Treasury officials have been devising policy on the fly for months now, as what began as a panic over losses on subprime mortgages broadened into a crisis that wreaked havoc on Wall Street, at major commercial banks and in the broader economy itself.

In September, Mr. Paulson went to Congress and urgently pressed for authority to spend as much as $700 billion to unclog the nation’s financial pipelines by buying up unsellable securities from banks and other financial institutions.

But by the time Congress approved the bailout law in early October, Mr. Paulson and the chairman of the Federal Reserve, Ben S. Bernanke, were already shifting to a strategy he had actually opposed: buying equity stakes directly in American banks, a move that was reminiscent of European-style nationalization.

As recently as a few days ago, Treasury officials insisted that they still intended to buy up the troubled assets. But by late October, it had become clear that Plan A had become little more than a sideshow.

“Illiquid assets looked like the way to go,” Mr. Paulson told reporters at a news conference on Wednesday. But as economic and financial conditions declined so rapidly, he said, that he had to change gears. “I will never apologize for changing the approach and the strategy when the facts change,” he said.