Presumptive Democratic nominee Barack Obama challenged his Republican opponent John McCain Wednesday to a 'duel' on taxes while touting his policies in a key swing state suffering from economic woes.

"These anxieties seem to be growing with each passing day," Obama told a crowd of over 1,500 inside a Springfield, Mo., high school gymnasium. "We can either choose a new direction for our economy or we can keep doing what we've been doing. My opponent, John McCain, thinks we're on the right track.

"I'm ready to duel John McCain on taxes right here, quick draw," Obama said, comparing himself to western legend Wild Bill Hickock who once fought a duel in Springfield.

The Illinois senator's remarks elicited a few boos from the audience, as well as a quick response from McCain campaign spokesman, Tucker Bounds, who said he's still waiting for a response on a previous proposal.

"We offered a civil version of a 'duel' in the form of 10 town hall meetings. Senator Obama has yet to take us up on that offer. We would be shocked but thrilled if we got a phone call at our campaign headquarters today to discuss our civil proposal."

In a letter released June 4, McCain invited Obama to a series of town halls -- the first one to begin June 12 and continue once a week until the Democratic convention in August.

“I’d be there on the 12th,” McCain wrote in the letter, “and I hope Sen. Obama will be there as well” in the “spirit of change” that could “do our country good.”

The town halls were to include about 200 to 400 people at each one, chosen by an “objective organization,” McCain said.

Obama campaign spokesman Tommy Vietor responded to Bounds' criticism by saying all of Obama's counter-proposals for joint appearances with McCain were rejected.

“We offered to do five joint appearances: three debates and two town halls, and the McCain campaign didn’t respond to us," Vietor told FOXNews.com “They didn’t tell us yes or no, they just let us know through the media that they didn’t think it was acceptable. They didn’t want to have a good faith discussion about it," he said.

Vietor also described as deceptive criticism of Obama's votes on tax policy in the U.S. Senate.

“To the claim that Obama voted to raise taxes 94 times, they [The McCain campaign] got hit by Factcheck.org on that because it is so misleading. Fact check.org described that claim as ‘inflated’ and 'misleading,'" Vietor said.

Obama was spending the day riding a bus across southwest Missouri, where Republicans have been dominant in recent elections, and arguing that he can bring new regions into play this election cycle because a sour economy is dominating the political landscape. He spoke to voters in the 7th District, which is represented by House Minority Whip Roy Blunt.

"It's true that change is hard, change isn't easy," Obama told the crowd. "Nobody here thinks that Bush or McCain has a real answer for the challenges we face so what they're going to try to do is make you scared about me."

Obama later added: "It's a leap, electing a 46-year-old black guy named Barack Obama," he said, noting that the message Republicans have for voters is simple: "He doesn't look like all those other presidents on the dollar bill."