WASHINGTON - Congressional leaders and the Bush administration have reached a tentative deal on a bailout of imperiled financial markets that could cost taxpayers hundreds of billions of dollars.

The House could vote on it Sunday and the Senate on Monday. House Speaker Nancy Pelosi announced the accord just after midnight Saturday and said it still has to be put on paper. Treasury Secretary Henry Paulson talked of finalizing the deal but added: “I think we’re there.”

The plan would spend up to $700 billion, most of it on buying deeply devalued mortgages from the housing market’s collapse and other bad loans held by tottering banks and other investors.

The aim is to prevent credit from drying up and causing a meltdown of the U.S. economy.

The House was scheduled to convene at noon CDT Sunday and members there were hoping they could vote on a bill by that evening and go home to campaign for re-election.

The Senate isn’t scheduled to go back into session until Monday.