At its core, the bill gives the Treasury Department $700 billion to purchase bad mortage-related securities that are weighing down the balance sheets of institutions that hold them. The flow of credit in the U.S. economy has slowed, in some cases drying up, threatening the ability of businesses to conduct routine operations or expand, and adversely affecting consumers seeking financing for mortgages, cars and student loans. Some state governments have also experienced difficulty borrowing money.

The House vote marked a sharp change from Monday, when an earlier measure was sent down to defeat, largely at the hands of angry conservative Republicans. A total of 33 Democrats and 25 Republicans switched from opposition to support. Several of the Democrats were members of the Congressional Black Caucus who said presidential candidate Barack Obama had pledged to support legislation easing the burden on consumers if he wins the White House.

Republican presidential candidate John McCain also lobbied for the measure, according to aides who declined to release a list of lawmakers he called.

Following Monday's vote, Senate leaders quickly took custody of the measure, adding on $110 billion in tax and spending provisions designed to attract additional support, then grafting on legislation mandating broader mental health coverage in the insurance industry. The revised measure won Senate approval Wednesday night, 74-25, setting up a furious round of lobbying in the House as the administration, congressional leaders, the major party presidential candidates and outside groups joined forces behind the measure.

In addition, the measure was changed to broaden the federal government's deposit insurance program, and the Securities and Exchange Commission loosened a regulation to ease the impact of the distressed assets on the balance sheet of financial institutions.

Despite occasionally strong criticism of the added spending and tax measures, the maneuvers worked — augmented by a sudden switch in public opinion that occurred after the stock market took its largest-ever one-day dive on Monday.

"No matter what we do or what we pass, there are still tough times out there. People are mad — I'm mad," said Republican Rep. J. Gresham Barrett of South Carolina, who opposed the measure the first time it came to a vote. Now, he said, "We have to act. We have to act now."

Rep. John Lewis, D-Ga., another convert, said, "I have decided that the cost of doing nothing is greater than the cost of doing something."

Critics were unrelenting.

"How can we have capitalism on the way up and socialism on the way down," said Rep. Jeb Hensarling of Texas, a leader among conservative Republicans who oppose the central thrust of the legislation — an unprecedented federal intervention into the private capital markets.

It was little more than two weeks ago that Paulson and Bernanke concluded that the economy was in such danger that a massive government intervention in the private markets was essential.