Obama, Clinton clash over gas tax as Indiana looms

"I think that would be good for our Democratic Party, it would be good for our democracy and it would be great for Indiana."

Their last debate in Philadelphia focused on Obama's controversial Chicago pastor and his recent relationship with a 1960s radical. Some Obama supporters criticized the moderators from television network ABC for not giving more weight to issues such as health care and the war in Iraq.

An Obama spokesman said the senator had participated in 21 debates already, including four with Clinton alone.

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

Clinton has seen some of her support from superdelegates and fund-raisers erode over accusations she has used negative campaign tactics, but her advisers say Obama's team has been just as negative.

Obama disputed concerns by some that he has not been aggressive enough in responding to Clinton's attacks.

"If you're really tough, sometimes you just walk away," he said.

(Editing by John O'Callaghan)

(To read more about the U.S. political campaign, visit Reuters "Tales from the Trail: 2008" online at blogs.reuters.com/trail08/)