Barack Obama and John McCain's campaigns switched into "Get out the vote" mode in more than a dozen battleground states Sunday, setting the stage for the climax of the $1 billion race for the White house.

For those at home searching for their calculators, that's about $8 spent for every single voter in the U.S.

Thousands of volunteers knocked on doors and made phone calls for each campaign in battleground states. 

"Go vote right now," Obama urged from the Ohio Statehouse steps, adding there was a nearby polling station open until sunset. "Do not delay because we have work to do."

Less than two days before the polling stations close in the 2008 campaign, Obama has an edge over McCain in national polls.

Surveys in all the all important battleground states, show that Obama has a much easier route to the 270 electoral votes needed to win the White House.

Already about 27 million absentee and early votes were cast in 30 states as of Saturday. Democrats outnumbered Republicans according to exit polls in key states.

Many Democrats said they were voting early because of fears about their vote on election day. There have already been numerous reports of voting problems, from three hour waits to vote machines switching votes, in many states, including Ohio and Florida.

Unlike in Canada, there is no federal voting body in the U.S. Instead there is a patchwork system of hundreds of state and local electoral authorities.

The Obama campaign already has 10,000 lawyers signed up via their website to help with potential voting problems.

McCain said he was "disturbed" about alleged voting irregularities.

New moves in final days

Both McCain and Obama have been reciting "wrap-up" speeches as the campaign comes to a close, but there were a few changes in store Sunday.

In New Hampshire, McCain held a "town hall" meeting, a forum the Arizona senator shines in, but has not used since Oct. 10. The move away from the forum came after McCain faced increasingly agitated crowds and occasionally racially-tinged comments aimed at Obama from supporters.

At one such town hall in October, McCain had to take away a microphone from a woman attacking Obama's character and background and then defend his opponent.

New Hampshire and Pennsylvania are the only two traditionally Democratic states that the McCain campaign is still contending in.

At the town hall meeting, McCain pushed for reform in Washington and had some tough words for some members of his own party, in particular, recently convicted Senator Ted Stevens of Alaska.

Obama is spending Sunday in Ohio, a state President George W. Bush won in both the 2000 and 2004 elections. He was introduced by Bruce Springsteen, who sang a number of songs for about 80,000 supporters in Cleveland, Ohio.

Obama in particular has kept to the script in the last weeks on the election, but had a new attack on McCain, razzing his opponent over Dick Cheney's endorsement.

Obama was upbeat and confident in Cleveland.

"The last couple of days, I've been just feeling good," he said. "The crowds seem to grow and everybody's got a smile on their face. You start thinking that maybe we might be able to win an election on November 4th."

McCain has embraced his underdog status and says he is coming back.

"I've been in a lot of campaigns. I know the momentum is there," McCain told supporters at a earlier rally in Pennsylvania Sunday.

Poll numbers have some Republicans wondering if McCain can catch Obama, who has enjoyed early momentum in key states like Nevada and Iowa, which were won by Bush in the last election.

McCain's campaign appears to need the biggest boost as an Associated Press-Yahoo News national poll of likely voters showed Obama ahead, 51 to 43, with a margin of error of plus or minus 3 percentage points.

Over the last few weeks, McCain's campaign has said its internal polling shows a narrower gap between the two candidates.

In the battleground states followed by Real Clear Politics' tracking of major polls, Obama has an advantage in many weekend polls:

• Florida: Obama +4.2
• North Carolina: Obama +1.3
• Virginia: Obama +5.0
• Ohio: Obama +5.8
• Missouri: McCain +0.6
• Colorado: Obama +5.5
• Nevada: Obama +5.8

The Obama campaign is also using its record-high cash flow to release new ads criticizing the Democrat's rival.

A new 30-second television spot released Sunday calls attention to McCain's unpopular choice of Alaska Gov. Sarah Palin to be his vice presidential running mate.

The ad also alleges that McCain's support for Bush administration policies is what led Vice President Dick Cheney to endorse McCain's candidacy, which he did on Saturday.

The ad repeats the charge that McCain sided with Bush 90 per cent of the time during the latter's eight years in the White House. "That's not the change we need," an announcer says.

McCain also took his campaign to the airwaves this weekend, poking fun at himself on NBC's Saturday Night Live alongside Tina Fey as Palin.

With files from The Associated Press