WASHINGTON (AP) -- Democratic presidential candidate Barack Obama said Sunday that race is not the reason he is struggling to attract working-class votes and insisted he can win over uncommitted superdelegates by showing he is "best able to not just defeat John McCain, but also lead the country."
Speaking in a broadcast interview, Obama also brushed aside a challenge from Hillary Rodham Clinton to debate before the May 6 primaries in Indiana and North Carolina. "I'm not ducking. We've had 21" debates, he said.
Trailing in delegates and the popular vote, Clinton has been stepping up the pressure on Obama for more debates before the upcoming primaries, which are crucial to her candidacy. She also has been reaching out to uncommitted Democratic superdelegates in hopes of capitalizing on her Pennsylvania primary victory.
Clinton's Pennsylvania victory was buoyed by support from working-class and white voters, but Obama dismissed the notion Sunday that race will be a factor in the presidential election.
"Is race still a factor in our society? Yes. I don't think anybody would deny that," he said on "Fox News Sunday."
"Is that going to be the determining factor in a general election? No, because I'm absolutely confident that the American people - what they're looking for is somebody who can solve their problems."
Addressing whether superdelegates should back the candidate with the most pledged delegates and popular vote, Obama said he believed voters will be frustrated if Democratic superdelegates choose to back the trailing candidate. He expressed confidence that he can convince superdelegates he is more electable.
"I think we should find that person who is going to be best able to not just defeat John McCain, but also lead the country. I happen to think I'm that person," Obama said. "I will make that argument forcefully to the superdelegates prior to the convention."
Speaking in Indiana to reporters, Obama declined to set expectations on a margin of victory in that state. Clinton was spending the day campaigning in North Carolina.
"I think winning is winning, 50 plus one," Obama said. "Indiana is a very important state, so is North Carolina, we're not taking that for granted. There's no doubt it's close. We feel very strongly that our message of bringing change to Washington is going to resonate in Indiana."
Democratic National Committee Chairman Howard Dean said superdelegates should make known their choices on the Democratic nominee for president by the end of June. Ultimately, he said he believes their decisions will be based on who is more electable, rather than necessarily who has the most pledged delegates, because that is what party rules stipulate.
"This is essentially pretty close to a tie here," Dean said on NBC's "Meet the Press."
"What's going to happen in the last nine primaries is there's going to be some feeling at some point that one of these candidates is more likely to win than the other and that person will get the nomination. I can't tell you who that is, I have no idea who that is, but that's what's going to happen," Dean said.
Dean also said he expected the party to heal from the bitter primary race if superdelegates make their decisions in June and that he believes Michigan and Florida delegates will be "seated in some way."
"If you go into the convention divided, it's pretty likely you'll come out of the convention divided," he said.
The Democratic Party stepped up its attack on Sen. John McCain, using a new party ad to cast the presumed Republican presidential nominee as a commander in chief who would keep troops in Iraq for 100 years. The ad is part of a half-million-dollar, three-week national cable television campaign aimed at linking the Arizona senator to the policies of President Bush.
The ad set to begin airing Monday accuses McCain of wanting to remain in Iraq for "maybe 100" years, a link to a remark McCain made in January while campaigning in New Hampshire. The ad concludes, "If all he offers is more of the same is John McCain the right choice for America's future?"
Since then, McCain has repeatedly said he has no intention of extending the war into the next century, but would keep a U.S. military presence in Iraq much as the United States has in Germany, Japan and South Korea.
The Republican National Committee charged that the DNC ad distorted McCain's comments, and it asserted again that the ad was illegal because it was made in coordination with the Obama and Clinton campaigns. Dean has denied any coordination with the campaigns.
The Democratic candidates have also acknowledged they would keep non-combat troops in Iraq to ensure its stability. But they have said they would begin withdrawing combat troops promptly upon becoming president, a step McCain has said would be precipitous.
Associated Press writers Mike Glover in Indianapolis and Jim Kuhnhenn in Washington contributed to this report.