MARION, Ind. — Democratic rivals Barack Obama and Hillary Rodham Clinton turned up the rhetoric Saturday 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.

Saturday, 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.