Democratic presidential candidate Senator Barack Obama boards a plane in St. Petersburg, Fla., on Thursday. (Alex Brandon/Associated Press)

Republican candidate John McCain still will not participate in a presidential debate set for Friday unless a consensus is reached between Congress and the U.S. administration on a $700-billion US bailout of the financial industry, a spokesman said.

"There's no deal until there's a deal. We're optimistic but we want to get this thing done," McCain spokesman Brian Rogers said.

McCain officially suspended his campaign Thursday morning.

By Thursday afternoon, key legislators in the United States reported they had reached an agreement in principle on the bailout package being proposed by U.S. President George W. Bush.

Details on the agreement in principle, which is meant to bail out the financial industry and avert a deeper economic crisis, had not been released as McCain and Democratic presidential candidate Barack Obama prepared to meet with Bush at the White House to discuss the rescue plan Thursday at 4 p.m. ET.

"With so much on the line, for America and the world, the debate that matters most right now is taking place in the United States Capitol — and I intend to join it," McCain said after addressing former president Bill Clinton's Global Initiative in New York Thursday before heading to Washington.

McCain said he was confident a bipartisan compromise could be reached before markets open Monday.

But Obama said Thursday morning the presidential debate set for Friday should proceed because Americans have a right to know how the next administration will lead the country out of its grave financial problems.

Leadership is needed now, Obama said before leaving Florida to head to Washington. Americans go to the polls on Nov. 4.

"Our election is in 40 days, our economy is in crisis, our nation is fighting two wars abroad," Obama said, speaking via satellite from Clearwater, Fla.

"The American people, I believe, deserve to hear directly from myself and Senator McCain about how we intend to lead our country. The times are too serious to put our campaigns on hold or to ignore the full range of issues that the next president will face."

Obama said "now is the time to come together" for the benefit of all Americans. He said he has no intention of suspending his campaign.

Debate organizers in Mississippi said they are continuing to prepare as though the debate will go ahead as scheduled.

Future of economy 'in danger': McCain

Earlier Thursday, McCain said American politicians must set their differences aside as they try to grapple with grave problems facing the economy.

"The whole future of the American economy is in danger," he said in New York City.

"If we do not act, credit will dry up with grave consequences for workers and businesses across the American economy and beyond. People will no longer be able to buy homes. Their life savings will be at stake. Businesses will not have enough money to pay their employees."

McCain said he officially suspended his campaign for now because he cannot proceed when there is so much at stake, given the fragility of the economy.

"I cannot carry on a campaign as though this dangerous situation had not occurred or as though a solution were at hand, which it clearly is not," he said.

Bush says plan needed to avoid economic pain

Bush called for the meeting with Obama and McCain in a nationally televised speech Wednesday night, where he warned that Washington's failure to pass the plan could cause "a long and painful recession.

"There is no question there are a lot of people who are opposed to aspects of it, but it's hard to find anybody who is prepared to vote directly down against the package itself," the CBC's Henry Champ said from Washington Thursday morning.

"So this meeting ought to be the kind of dam breaker that is necessary."

The bailout plan was initially met with opposition from Republican and Democratic congressional leaders, as well as many of their constituents, over its high cost. Many congressional leaders have also called for government oversight of the distribution of the package.

But the administration cleared a major sticking point by agreeing to limit pay packages to executives of the failing companies.

Among the issues still to be worked out is how to phase in the cost of the plan, whose implementation the future president will have to oversee after he is sworn in.

With files from the Associated Press