Democrat Barack Obama and Republican John McCain raced through the battleground states of Ohio and Pennsylvania on Sunday, with McCain struggling to overtake Obama's lead in the final 48 hours of the fight for the White House.

Obama warned against overconfidence at a rally in Columbus, Ohio, one of about a dozen crucial battleground states that will decide a race to succeed unpopular US President George W. Bush lasting two years and costing more than $2 billion.

"Don't believe for a second that this election is over," Obama, who would be the first black US president, told a crowd estimated at more than 60,000 by Columbus police. He urged them to vote and knock on doors on his behalf as the campaign hurtles toward Tuesday's election.

"We can't afford to slow down, sit back, or let up for one day, one minute, or one second in these last few days," the Illinois senator said.

McCain reached out to undecided voters in Pennsylvania, his best and perhaps last hope of stealing a Democratic-leaning state from Obama as the two candidates search for the 270 electoral votes needed for victory.

The Arizona senator is battling to wipe out Obama's lead in every national opinion poll and in many key states, and he and his top aides said he was closing the gap at the end.

"My friends, I've been in a lot of campaigns. I know when momentum is there," he said in Wallingford, Pennsylvania. "We're going to win Pennsylvania and we're going to win this election. I sense it and I feel it and I know it."

McCain planned a whirlwind day of campaigning featuring two stops in Pennsylvania, an appearance in New Hampshire and a post-midnight rally in Miami, Florida. He'll wind up the race on Monday with stops in seven states, including his home of Arizona.

"What we're in for is a slam-bang finish," McCain campaign manager Rick Davis said on "Fox News Sunday."

"He's been counted out before and won these kinds of states, and we're in the process of winning them right now," Davis said of big battleground states like Ohio, Florida and Virginia.

Playing Defense

A flurry of new opinion polls on Sunday offered only slight evidence to back up Davis's claim. One new survey showed McCain slightly ahead in Ohio, although others showed Obama leading.

Obama has an edge in most other key battleground states, although his advantage has been whittled down in Florida, Virginia, Nevada and Pennsylvania.

McCain must defend about a dozen states won by Republican Bush in 2004, and needs to win nearly all of them.

Both candidates drove home their main themes in the final days of the race, with Obama linking McCain to Bush and adding a new twist with an advertisement tying McCain to the equally disliked Vice President Dick Cheney.

"I'm delighted to support John McCain," Cheney says in the ad, shot at a campaign event on Saturday in Wyoming. He also praises McCain's running mate, Alaska Gov. Sarah Palin. "That's not the change we need," the ad's announcer said.

McCain continued to slam Obama as a liberal who would raise taxes on small businesses. Obama has said he will raise taxes on those making more than $250,000 a year.

As Obama boarded his campaign plane for Ohio on Sunday morning in Missouri, a reporter asked how he would structure the $700 billion bailout of US financial firms recently approved by Congress.

"We're on a tarmac," Obama replied. When the reporter asked why he would not hold a news conference, Obama said: "I will. On Wednesday." A campaign spokeswoman later said plans for a news conference were not firm but it would be sometime this week.

In Ohio, Obama offered rare praise for McCain, applauding his comic turn on NBC's "Saturday Night Live."

"John McCain was funny yesterday on 'Saturday Night Live,'" Obama said. "That's part of what politics should be about, being able to laugh at each other but also laugh at ourselves."

Obama's campaign has focused on getting supporters to vote early, hoping to lock in backing from new and sporadic voters who otherwise might not turn out to the polls. An estimated 30 percent of voters will have cast their ballots by the time polls open on Tuesday, and Democrats have been encouraged by the early results.

Obama's chief strategist, David Axelrod, noted Democrats have had an advantage in early voting in key states like Colorado and Florida.

"In Colorado last time, the Republicans had an 8-point edge in early voting. We have an edge now," Axelrod said on ABC's "This Week."

"In Florida, they finished early voting and absentee voting 40,000 votes ahead. We think we're going to have a 350,000 vote edge," he said.

Editor: Yan