WASHINGTON  The Senate strongly endorsed the $700 billion economic bailout plan on Wednesday, leaving backers optimistic that the easy approval, coupled with an array of popular additions, would lead to House acceptance by Friday and end the legislative uncertainty that has rocked the markets.

In stark contrast to the House rejection of the plan on Monday, a bipartisan coalition of senators  including both presidential candidates  showed no hesitation in backing a proposal that had drawn public scorn, though the outpouring eased somewhat after a market plunge followed the House defeat. The Senate margin was 74 to 25 in favor of the White House initiative to buy troubled securities in an effort to avoid an economic catastrophe.

Only Senator Edward M. Kennedy, who is being treated for brain cancer, did not vote.

The two Senate leaders, Senators Harry Reid, Democrat of Nevada and the majority leader, and Mitch McConnell of Kentucky, the Republican leader, strongly urged their colleagues to approve the plan despite the political risk given public resentment.

“Supporting this legislation is the only way to make the best of a crisis and return our country to a path of economic stability, prosperity and growth,” said Mr. Reid, who asked that senators vote formally from their desks. The presence in the Senate of both presidential candidates in the final weeks of the campaign also gave weight to the moment. The political tension was clear as Senator Barack Obama walked to the Republican side of the aisle to greet Senator John McCain, who offered a chilly look and a brief return handshake.