If Sen. Barack Obama wakes up as the president-elect on Nov. 5, he will immediately assume responsibility for fixing a shredded economy while the Bush administration is still in office. If Sen. John McCain wins the election, he will face an imminent confrontation over spending with a Democratic Congress called back into special session with the goal of passing a new economic stimulus package.

Either way, the 77-day period between Election Day and Inauguration Day, traditionally known simply as the transition, is sure to present difficult challenges to a new president buffeted by intense forces, political and economic, without any chance to recover from the long and bruising campaign.

The challenge of putting the country back on a sound financial track has altered what under the best of circumstances would have been a frenzied period spent forming a new government. Instead, Obama or McCain will be forced to assemble a new administration even as he helps shape policies to ward off further declines in the economy.

And whoever is the new president will be under intense pressure from his own allies to live up to his campaign promises. Antiwar groups would press Obama to start the process of ending the war in Iraq, and conservatives would demand tax cuts from McCain. Either side would want to know that its candidate has an agenda to enact on his first day in the White House. With the outcome of the election still in doubt, neither campaign is eager to discuss plans for that day or the transition that precedes it, other than to acknowledge the urgent circumstances the 44th president will confront.

"I don't think he's thinking about [Inauguration Day on] January 20," said one top Republican involved in the McCain campaign. "He's thinking about November 5."

David Axelrod, Obama's chief political strategist, promised last week that if "we are successful, we will be ready to act quickly to put our plan in place."

McCain has tapped John F. Lehman, a close friend who was a Navy secretary in the Reagan administration, to lead the transition. Former Clinton White House chief of staff John Podesta is running Obama's effort.

Neither would be interviewed for this article, but advisers to both campaigns say they are aware of the problems that can arise if careful thought is not given to how to handle those first days and weeks. They believe that much of President Bill Clinton's ineffectiveness in his first year can be traced to bad decisions during the transition and his first days in office. And this year's economic crisis is certain to heighten those concerns, both sides said.

Those involved in planning a possible McCain transition say he is genuinely interested in bipartisan governing and would immediately reach out to the opposition. But his interest in working with the other party may run afoul of the likely rage many Democrats will feel if the White House slips from their grasp in the final weeks of the 2008 campaign.

"If they lose this one, you are going to have a lot of really angry Democrats," said Rep. Paul D. Ryan (Wis.), a McCain ally and the ranking Republican on the House Budget Committee.

Top advisers said McCain would move quickly to implement the economic agenda he has promised, including tax cuts, business incentives, lower trade subsidies and controls on government spending that he says are bankrupting the country. But Democratic leaders have already signaled their intention to pass a stimulus package during November's lame-duck session.

"If they try to put together a $300 billion stimulus package that's throwing money at problems -- feel-good money -- and we haven't gotten the accountability and reform in place, then we'll have a fight," predicted Sen. Lindsey O. Graham (R-S.C.), a McCain confidant.