WRAPUP 2-Obama, Clinton clash over gas tax as Indiana looms

(Adds Obama campaign statement on debate)

By Jeff Mason and Andy Sullivan

ANDERSON/SOUTH BEND, Ind., April 26 (Reuters) - Democrats Barack Obama and Hillary Clinton touted their economic agendas and sparred over fuel taxes on Saturday as they crisscrossed Indiana ahead of its must-win U.S. presidential nominating contest in May.

Clinton, a New York senator who trails Obama in votes and number of delegates who will determine the party's nominee to run in November's election, challenged the Illinois senator to a televised debate without moderators. His campaign declined.

Obama gave a populist message as he tried to reach the kind of working class voters who handed victory to Clinton in Tuesday's Pennsylvania primary election.

"If the economy's growing and your incomes are going down, what's happening? It means that somebody's making out like a bandit," Obama told about 2,000 people in the city of Marion, citing tax cuts under the Bush administration that benefited the wealthy and not the middle class.

Obama spoke out against halting a tax on gasoline during the summer months, a move supported by Clinton and presumptive Republican nominee John McCain, saying it may not bring down prices and would deplete a fund used for building highways.

"The only way we're going to lower gas prices over the long term is if we start using less oil," Obama said in Anderson.

Indiana holds its nominating contest on May 6 and polls show the race to be tight. Like other Americans, the state's residents are concerned about high fuel prices, a mortgage crisis, job losses and a sputtering economy.