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CHICAGO - The political rivalry between President Barack Obama and Republican budget maven Paul Ryan entered a new phase today as both men vie for the spotlight and swing votes in the key presidential battleground of Iowa.

Obama embarks on a bus tour from Council Bluffs, in the western part of the state, cutting across the drought-stricken farmland over three-days to hit seven stops along the way. It marks his most aggressive effort of the year in the state that catapulted him to the presidency four years ago.

Ryan, fresh off his debut as vice presidential running mate for Mitt Romney, will "drop by" the Iowa State Fair in Des Moines on his first solo day of stumping for the GOP ticket. The novelty of his new role is sure to draw curious crowds.

Iowa is fitting turf for a first campaign clash between the two men and their starkly contrasting economic visions for the country. The most recent polling shows Obama and Romney locked in a dead heat in the state, unlike several other battlegrounds where Obama has developed a slight lead.

"I need you guys to load up and go over into Iowa, a battleground state, and knock on some doors and make some phone calls over there," Obama told a young crowd of donors here Sunday afternoon. "We've got to get help. You've got to get involved in the election."

Republicans hope Ryan's Midwestern charm and sense of pragmatism will have particular appeal in Hawkeye country, especially on issues of deficits and debt. They say Obama's jam-packed itinerary shows he knows he's vulnerable.

"It looks likes someone's worried about his diminishing reelection prospects. And rightfully so," said Republican National Committee political director Rick Wiley.

"Iowa voters are disappointed in the president. He has proven not be the leader he promised to be. Despite his feverish campaigning, he's becoming less popular," he said, noting that Obama carried the state by nine points over John McCain in 2008.

The Obama campaign shrugs off the pessimism as partisan spin, insisting Iowa voters will reject the Romney-Ryan ticket when they learn about a tax plan that they say would hike rates on the middle class.

"During his first term, President Obama has already cut taxes for a typical Iowa family by about $3,600. This has helped Iowa families afford to send their children to college, buy their first home, pay for health care and child care," the campaign said in a statement.

Democrats have been mobilizing an army of grassroots volunteers in Iowa since before the caucuses in January, and dozens of staff now coordinate voter education and registration efforts out of a notable 20 offices across the state.

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