The plan for the largest-ever bank rescue would give sweeping powers to the U.S. Treasury to buy up toxic mortgage-related debt from financial firms, including U.S. subsidiaries of foreign banks.

Follow the Money: What's in the Bailout Plan

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Democratic leaders in Congress promised swift action, but also want to throw a lifeline to homeowners, not just Wall Street.

With the economy issue No. 1 in an election less than six weeks away, lawmakers are striving to get a plan in place by week's end, fearful that delay could send markets reeling.

"This is a new phenomenon for every major player in this place and there are no dress rehearsals. That is why the market is so jittery. This has to work the first time," said Peter Kenny, managing director at Knight Equity Markets in Jersey City, New Jersey.

Altogether, the plan could end up costing $1.8 trillion. Click here for details

The bailout plan follows a wrenching week that transformed Wall Street with Lehman Brothers' failure, the agreed sale of Merrill Lynchand a government takeover of ailing insurer AIG .

It was also possible that within days one of the two remaining U.S. investment banks -- Morgan Stanley—would accept a partner.

Two key questions remained unanswered even after Treasury Secretary Henry Paulson appeared on four television talk shows to press his case for emergency action.

For Investors

What price will the United States pay for these toxic debts, which have spawned the worst financial storm since the Great Depression? When will it start buying them?

"I'm confident that the credit market will improve but it will improve slowly. It just seems a lot of details have not been answered yet," said Jack Ablin, chief investment officer with Harris Private Bank in Chicago.

Paulson painted the proposed market intervention as a necessary evil, arguing the consequences of inaction would be so dire that the large burden on taxpayers would be worth it.

"This is not something that we wanted to do. This was something that was very necessary," Paulson said on the NBC Sunday program "Meet the Press." "We did this to protect the taxpayer."