"At this point, Congress is being asked to support an uncertain entity, costing an uncertain amount of dollars, for an uncertain duration - a decision that will have implications for generations to come and requires absolute certainty," said Rep. Jeb Hensarling, a Texas Republican and leader of House conservatives.
"My fear is that taxpayers will be left with the mother of all debts."
Meanwhile, Democrats charged that the White House plan would offer too much help to financial companies that bet big on risky mortgage investments, and not enough to people losing their homes to foreclosure.
They expressed irritation with what they described as Paulson's insistence that Congress approve the administration proposal "clean," without any aid for troubled homeowners or regulations aimed at preventing a repeat of the current disaster.
Even policy analysts who generally are not averse to government intervention in the economy seemed taken aback by the apparent scale and aggressiveness of what the administration and the Fed have in mind. Robert E. Litan, a Treasury official with the Clinton administration who is a senior analyst with the Brookings Institution, said the new plan seemed to invite banks and securities companies to dump their very worst assets on the government with no clear way to get rid of them.
"What they're going to get is the financial equivalent of radioactive waste," he warned.
In Florida, Sen. Barack Obama of Illinois, the Democratic presidential nominee, said he would press for a broader economic stimulus initiative to be part of the bailout plan for financial firms.
Aides said Obama was still reviewing the administration's proposal. But in Daytona Beach, Fla., he told voters, "We have to make sure that whatever plan our government comes up with works not just for Wall Street, but for Main Street."
He added: "We have to make sure it helps folks cope with rising prices, and sparks job creation, and helps homeowners stay in their homes. That's the kind of help folks need right now."
Mindful of such sentiments, not just by Obama but by his rival, Sen. John McCain of Arizona and other Republicans, Paulson and Bernanke held a series of conference calls with members of Congress on Friday to begin selling them on the proposal, and to assure them that action was needed not just to help Wall Street but everyday Americans as well.
They emphasized that the risk of steep declines in worldwide markets posed a grave risk to all Americans, especially their retirement plans and college savings for children but also their access to consumer credit, including auto loans.
Bernanke, for instance, pointed out that many Americans have savings invested in money market funds, which were at risk of unexpected losses.
Even as congressional staff members began to scour the proposal, a host of questions remained.
One of the few limitations set forth in the plan would limit the Treasury's ability to buy mortgage-related assets only "from any financial institution having its headquarters in the United States."
That would seem to preclude the administration from buying assets from firms like UBS, the giant Swiss bank, which has a huge stake in American mortgage-backed securities.
The New York Times contributed to this article.
