( Reuters ) - White House hopefuls dashed across Iowa in a hunt for votes on Wednesday, with Hillary Clinton and her two top rivals scrambling to avoid third place in a tight opening round of voting for the U.S. Democratic presidential nomination.
On the Republican side, Mitt Romney and Mike Huckabee took divergent paths to Thursday's showdown in Iowa: Romney chased support in frigid Iowa, while Huckabee flew to sunny California for a television appearance on comedian Jay Leno's "Tonight Show."
Clinton, a New York senator, Illinois Sen. Barack Obama and former North Carolina Sen. John Edwards are in a three-way battle among Democrats.
A third-place finish for any of them would be a serious setback, slowing their momentum and raising doubts about the future of their campaigns.
Edwards swiped at corporate greed in an editorial in the Wall Street Journal, and all three Democrats paid to air closing messages on Iowa television.
"If you stand with me for one night, I will stand up for you every day as your president," Clinton told voters in a two-minute message airing on Iowa television stations in the evening, before Thursday night's caucuses.
Iowa is the first test of the state-by-state battle to choose presidential candidates in November's election, and a Reuters/C-SPAN/Zogby poll on Wednesday showed the races on both sides essentially deadlocked.
Clinton and Obama were tied among Democrats at 28 percent, with Edwards close behind in a statistical dead heat at 26 percent.
Huckabee led Romney by two points, well within the poll's margin of error, with Arizona Sen. John McCain and former Tennessee Sen. Fred Thompson tied for a distant third.
The Democratic caucus begins at 6:30 p.m. CST (7:30 EST), with Republicans starting 30 minutes later. Results could begin to appear within an hour or two.
The U.S. presidential race is the most wide open in a half-century, with no sitting president or vice president running for the first time since 1952.
Clinton, Obama and Edwards dashed back and forth across the state to ask supporters to show up for them on Thursday.
"I promise you this -- we will not just win the caucus, we will win the primary, we will win the general election and we will change this nation and change the world," Obama told a rally in Davenport.
Edwards, in the midst of a 36-hour marathon sprint around the state, campaigned through the night. He has been inching up in polls and drawn fire from both Clinton and Obama recently.
"We are excited by your energy and enthusiasm. We are sort of running on adrenalin right now," he told an audience of several dozen supporters who crowded into a home in Centerville at 5:15 a.m. CST. "But we feel very good about how things are going."
In the Journal opinion piece, he said chief executives now earn 400 times the average salary. "The problem is that the successes of our economy are no longer shared," wrote Edwards.
Huckabee, the former Arkansas governor, planned to return to Iowa immediately after taping his "Tonight Show" appearance.
"We'll still be campaigning, in the meantime more people will see me in Iowa on Jay Leno tonight," said Huckabee, the former Arkansas governor. Leno's show is the top-rated late-night talk show on U.S. television.
"I guess he's more focused on the caucus in L.A. than the caucus in Iowa," countered Romney, the former Massachusetts governor.
McCain, who has largely bypassed Iowa to focus on next Tuesday's primary contest in New Hampshire, returned to Iowa on Wednesday after campaigning in New Hampshire earlier in the day with Connecticut Sen. Joseph Lieberman, a Democrat turned independent who has endorsed him.
"We like the enthusiasm, we're moving forward and we're happy with the progress we're making and we're eagerly looking forward to next Tuesday," McCain said during a visit to a New Hampshire diner.
Campaigning in New Hampshire, former New York Mayor Rudy Giuliani called for a doubling of U.S. combat troops in Afghanistan as part of a broader military expansion.
"We need to bring a surge to Afghanistan and make it effective right now," he said in Wolfeboro. He was referring to the increase of U.S. troops in Iraq credited with dampening violence there.
Giuliani, who has not focused on Iowa to concentrate on later voting states, has seen his poll numbers decline nationally and in the states in recent weeks.