Senators have reached a tentative deal on a version of President Obama's economic spending plan, including about $811 billion in spending and tax cuts, that will win enough Republican votes to move forward.

Sens. Arlen Specter of Pennsylvania and Susan Collins of Maine appeared to be the critical Republicans to sign onto the bill, giving Democrats the 60 votes needed to advance to a final vote. Democrats also voiced confidence that Republican Sen. Olympia Snow of Maine also would vote for the plan.

It isn't certain when a vote would come, but Democratic leaders said it could possibly come Tuesday.

The agreement capped a tense day of backroom negotiations in which Senate Majority Leader Harry Reid, joined by White House chief of staff Rahm Emanuel, sought to attract the support of enough Republicans to give the measure the needed majority.

Uncertain of the outcome of the talks, Democrats called Sen. Edward M. Kennedy back to Washington in case his vote was needed. The Massachusetts senator, battling brain cancer, has been in Florida in recent days and has not been in the Capitol since suffering a seizure on Inauguration Day more than two weeks ago.

Reid, who had sought Friday to cut just $63 billion in spending from the bill, throwing a monkey wrench into the talks, called it an imperfect compromise. He warmly praised it nonetheless.

"But at the end of the day, we are passing a bold and responsible plan that will help our economy get back on its feet, put people to work and put more money in their pockets," Reid said.

As part of the deal, spending in the bill was reduced while tax cuts were increased, for a mix of 58 percent spending and 42 percent tax cuts. A senior Democratic leadership aide said the White House was on board.

But Republican leaders still worry the bill contains too much spending on programs that won't stimulate the economy, with Minority Leader Mitch McConnell saying Friday night on the floor of the Senate arguing that "the big spending programs of the New Deal did not work."

Obama is pushing for the massive spending plan to jump-start the economy, which otherwise, he says, could be headed for "catastrophe."

Specter said Friday night that action was "very necessary," and this bill, though not perfect, is better than inaction.

"I think no one could argue with the fact that the situation would be much worse without this bill," Specter said at a news conference.

The president has taken an increasingly public approach to advocating the bill's passage, sitting for TV interviews early this week and planning trips to Indian and Florida next week to promote the measure. Polls suggest taxpayers are skeptical about the effectiveness of the plan. 

The two cities Obama will visit next week have struggled amid the crumbling economy. Elkhart, Ind., has seen its unemployment jump to 15.3 percent from 4.7 percent in the past year and unemployment in Fort Myers, Fla., has climbed to 10 percent.

The House passed a economic stimulus package of a little more than $800 billion last month with Republicans unified against the measure. In Senate deliberations, the price tag had risen higher than $900 billion, prompting Senate Republicans to complain that it contained too much spending and not enough tax relief.

Even Democratic Sen. Dianne Feinstein of California voiced opposition to the bill on Friday, saying it wouldn't do enough to stimulate the economy. But after news broke Friday night that a deal had been reached, Feinstein said, "This is as good a compromise as we are going to get."

The White House voiced optimism that progress was being made.

"On the day when we learned 3.6 million people have lost their jobs since this recession began, we are pleased the process is moving forward and we are closer to getting Americans a plan to create millions of jobs and get people back to work," White House Press Secretary Robert Gibbs said in a written statement.

FOX News' Trish Turner contributed to this report.