"I don't know about you but I am feeling great!" she said at her first event in Ames. Working hard to grab the momentum, Clinton joked about the extremes to which she would go to win support, recalling a campaign appearance among farmers and ranchers in an arena that normally is the site of cattle auctions.

"If you want to look inside my mouth to figure out whether you want to vote for me, that's fine, too," Clinton quipped. "Whatever it takes."

Edwards also brought his wife and two young children along for the final push, a "marathon for the middle class" during which he will continue to hammer away at pocketbook issues on an overnight drive to energize backers and deliver them to the caucuses.

"We hope for the next 36 hours that all of you will be as focused and energized as we are," he said, beginning the tour with a rally before about 500 people jammed into a ballroom at the student union at Iowa State University in Ames.

All three also turned to the airwaves to urge voters to attend caucuses.

Clinton and Obama were to air longer-than-usual, two-minute ads during Wednesday's evening news programs. Edwards bought a full-page ad in the Des Moines Register featuring a testimonial from a worker who was laid off from an Iowa Maytag plant. The worker also will appear in a one-minute TV ad for Edwards.

In a sign of the increasingly heated battles beyond Iowa, McCain, who isn't playing Iowa as aggressively as he is New Hampshire, opened a new line of criticism against Romney in a new Web video that could end up on TV. "Mitt Romney says the next president doesn't need foreign policy experience," it says.

Conversely, Romney rolled out a Web video skewering McCain, and began airing a TV ad in New Hampshire that pivots from his criticism of his rivals and urges people to "vote for tomorrow."

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Contributing: Mike Glover, Nedra Pickler, Beth Fouhy, Ron Fournier, Amy Lorentzen, Libby Quaid and Nafeesa Syeed in Iowa, and Philip Elliott in New Hampshire