MARION, Ind. — Democratic rivals Barack Obama and Hillary Rodham Clinton turned up the rhetoric yesterday in their increasingly heated primary battle as she issued a new debate challenge and he complained of a race that's largely been reduced to trivia while working families feel economic pain.

Clinton took the debate dispute to a new level, challenging Obama to face off with her in a debate without a moderator, Lincoln-Douglas style.

"Just the two of us, going for 90 minutes, asking and answering questions, we'll set whatever rules seem fair," Clinton said while campaigning in South Bend.

Her campaign made the offer formal with a letter to the Obama campaign.

Obama aides said he had already debated Clinton 21 times, "the most in primary history."

"Over the next 10 days, we believe it's important to talk directly to the voters of Indiana and North Carolina," said Obama spokesman Robert Gibbs.

The more open style of debating where each side presents an argument gets its name from the famed debates that took place during the 1858 U.S. Senate race in Illinois between Republican Abraham Lincoln and Democrat Stephen Douglas.

Trailing in delegates and the popular vote, Clinton has been stepping up the pressure on Obama for more debates in advance of primaries on May 6 in Indiana and North Carolina. Clinton argued that Obama won't debate because he's unhappy with questions from moderators during the April 16 debate just before the Pennsylvania primary. After that debate, Obama complained it focused too much on political trivia and too little on real issues.

On the campaign trail yesterday, he sounded much the same theme.

"I was convinced that the American people were tired of the politics that's all about tearing each other down. The American people were tired of spin and PR; they wanted straight talk and honesty from their elected officials," Obama said at a town hall meeting in the aging industrial city of Anderson.

"If you watched the last few weeks of this campaign, you'd think that all politics is about is negative ads and bickering and arguing, gaffes and sideline issues," Obama said. "There's no serious discussion about how to bring jobs back, to Anderson."

Both rivals were focusing on Indiana, with Clinton bringing along popular Sen. Evan Bayh and talking about reviving the industrial economy.

"We can do that again, but we need, as Senator Bayh said, a president who doesn't just talk about it but who actually rolls up her sleeves and gets to work," said Clinton.

The two Democratic candidates were stumping in the heart of Republican territory, and Obama sought to reach across party lines, saying he's struggled to avoid the back-and-forth bickering of the campaign, and talk about issues like plant closings that have damaged cities like Anderson.

"I've been trying to resist that in this campaign and I will continue to resist it when I'm president of the United States," said Obama.

Clinton campaigned in eastern Indiana industrial pockets, seeking to build a coalition of working-class voters similar to the one that served her well in neighboring Ohio.

While the upcoming primaries in Indiana and North Carolina are crucial to her candidacy, but Clinton deflected questions about how she would handle a loss.

"I don't make predictions or speculate on things that haven't happened yet," said Clinton.

Obama is favored in North Carolina, but the polls have shown the race in Indiana far too close to call.

With no end in sight soon for the Democratic contest, Obama sought to ease worries that the intraparty fight will leave the party vulnerable in November.

"Everybody is kind of nervous about this Democratic primary; it's been going on a long time," Obama said. "I have my differences with Senator Clinton and she has her differences with me. We will be united in November and beat John McCain and the Republicans."

Obama also underscored his differences with McCain, the certain GOP nominee.

"John McCain says he's different, but when you look at his policies he's got no agenda for you, how to make you a little more successful," Obama told his heavily blue-collar audience. "We know in our hearts that this country is not going down the right track. Something needs to change right now and that's what's at stake in this election."

In Anderson, Obama noted that McCain has switched views on issues like tax cuts for the rich to curry favor with the GOP base. "The straight talk express lost a wheel," Obama said.

"This again shows that Barack Obama doesn't understand the economy. Americans are looking for proof that the next president is going to be someone who understands their needs," McCain spokesman Tucker Bounds said in a statement.

While Clinton was busy campaigning in the Hoosier state, husband Bill was looking ahead to Oregon's Democratic primary on May 20.

In Albany, Ore., he outlined his wife's plans for energy independence, and highlighted her vote against a Bush administration bill that gave final say over the siting of liquefied natural gas terminals to the federal government, instead of the states. Several such terminals are under consideration now in Oregon.