Now they take the themes from an intense first debate back to the campaign trail, looking for some edge in a tight presidential race. With 38 days left, McCain is headed for Washington and the dispute over a Wall Street bailout, while Obama plans to visit Republican-leaning states where the Democrat thinks he can make inroads.

The debate presented a huge opportunity for the candidates to deliver their message to millions of Americans — or make an embarrassing blunder.

Interest in Friday's debate was amplified by suspense about whether it would even take place. McCain had said he wouldn't take part unless the financial crisis was resolved, then reversed course and decided at the last minute to participate without a deal.

McCain, 72, frequently referred to his age and experience.

Sometimes he joked — at one point he waggled his eyebrows and quipped that the moderator didn't think he could hear the question — and other times he went out of his way to mention the foreign countries he has visited and the years he has spent on Capitol Hill.

"I have a long record and the American people know me very well," he said.

But Obama, a 47-year-old serving his first term in the Senate, challenged McCain frequently and offered himself as someone who can be trusted to make sound choices.

Obama noted that he opposed invading Iraq, while McCain supported it. He said McCain has voted with the unpopular President Bush 90 percent of the time. He argued McCain backs corporate tax breaks and lax regulation that have contributed to the Wall Street economic crisis.

"We have to recognize that this is a final verdict on eight years of failed economic policies promoted by George Bush, supported by Senator McCain," Obama said.

Obama sought to connect with voters who might have doubts about a relative newcomer to national politics, a black man with an exotic name and background. He talked often about the struggles of ordinary Americans — "the nurse, the teacher, the police officer who, frankly, at the end of each month they've got a little financial crisis going on."

The Obama campaign tried to back up that point in its newest ad, a spot released Saturday that notes McCain never mentioned the middle class during the debate. "McCain doesn't get it," the announcer says. "Barack Obama does."

In a long exchange with McCain over the Iraq war, Obama tried to avoid being seen as soft or reluctant to use force when necessary.

An early opponent of invading Iraq, he stressed that his position was prompted partly by worries that it would distract from hunting down Osama bin Laden, and he said withdrawing from Iraq now would free up resources to re-energize that hunt.

Obama suggested McCain might overreact to national emergencies, noting that the Arizona senator has talked about "extinction" for North Korea and joked about bombing Iran.

McCain accused Obama of seeking to "snatch defeat from the jaws of victory" in Iraq. He said the "surge" of U.S. troops has reduced violence there and withdrawing would destabilize the country and the entire region.

Asked what lessons he had learned from the long war, McCain said, "that you cannot have a failed strategy that will then cause you to nearly lose a conflict."

In its first post-debate TV ad, the McCain campaign accused Obama of "playing politics ... risking lives" when he voted against a war spending bill in May 2007, supporting the charge that Obama's "not ready to lead" with criticism from that time by Joe Biden, now Obama's running mate. When McCain cited that vote during the debate, Obama defended it as being aimed at the lack of a withdrawal timetable, not at funding for troops.

On Iraq and many other issues, McCain said Obama was naive, experienced, confused. He criticized Obama for saying he would meet with Iranian President Mahmoud Ahmadinejad without precondition. "This is dangerous. It isn't just naive; it's dangerous," McCain said.

The two bickered at times, talking over one another and throwing accusations of twisted words and false statements. But Obama sometimes acknowledged agreements with McCain — concessions that might reinforce Obama's claim to be a politician who can find common ground and reduce confrontation in Washington.

The stakes were high as the two rivals walked on stage. The polls gave Obama a modest lead and indicated he was viewed more favorably than his rival when it came to dealing with the economy. But the same surveys show McCain favored by far on foreign policy.

The candidates stood behind identical wooden lecterns on stage at the performing arts center at the University of Mississippi for the first of three scheduled debates with less than six weeks remaining until Election Day. The two vice presidential candidates will meet next week for their only debate, and Obama and McCain each put in a plug for his own running mate.

But there was a difference: Biden made the round of post-debate television shows. NBC and CNN said they invited McCain's running mate, Alaska Gov. Sarah Palin, who has granted only three interviews since joining the ticket a month ago, but she declined.

Moderator Jim Lehrer's opening question concerned the economic crisis. While neither man committed to supporting bailout legislation taking shape in Congress, they readily agreed lawmakers must take action to prevent millions of Americans from losing their jobs and their homes.

Both also said they were pleased that lawmakers in both parties were negotiating on a compromise.

Neither could offer specifics about how the potential $700 billion price tag of a Wall Street bailout might affect their ability to implement all the campaign promises they've made.

McCain jabbed at Obama, who he said has requested millions of dollars in pork barrel spending, including some after he began running for president. As he does frequently, the Republican vowed to veto any lawmaker's pork barrel project that reaches his desk in the White House.

McCain said a freeze on most government spending was worth considering, except for veterans, defense and "some other vital issues."

Obama said the problem with that was that some programs needed more money. He mentioned early childhood education as an example.

"The problem with a spending freeze is you're using a hatchet where you need a scalpel," he said.

The presidential hopefuls are scheduled to debate twice more, at Belmont University in Nashville on Oct. 7 and at Hofstra University in Hempsted, N.Y., on Oct. 15.

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Associated Press writer Beth Fouhy contributed to this report.