DES MOINES, Iowa – After a yearlong run-up, Iowa voters today finally will begin to unravel two fiercely contested presidential nominating contests that have confounded political handicappers.

With the Democratic and Republican races too close to call, the outcomes likely will depend on which campaigns do the best job of getting their supporters to the Iowa precinct caucuses on what is expected to be a clear but very cold winter night.

The Democratic contest has come down to a three-way battle among Sen. Barack Obama of Illinois, Sen. Hillary Rodham Clinton of New York and former Sen. John Edwards of North Carolina. In the end, they returned to their main campaign themes: experience for Clinton, change for Obama and fighting special interests for Edwards.

On the Republican side, former Arkansas Gov. Mike Huckabee and former Massachusetts Gov. Mitt Romney are neck and neck in the latest polls, with Sen. John McCain of Arizona and former Sen. Fred Thompson of Tennessee in contention for third place.

The closeness of the races was reflected in a frenetic final-day campaign schedule, particularly on the Democratic side. The leading Democrats held 34 separate events across the state, with Edwards skipping sleep and starting the day with an event in Creston at 2:15 a.m.

Among her other activities, Clinton taped a cameo introduction for the return of CBS' “Late Show with David Letterman” after a two-month hiatus because of the ongoing Hollywood writers' strike.

Republicans were less active, with the leading candidates holding 14 events.

Several Republican candidates spent part of the day on conservative talk-radio shows. Huckabee even left the state to appear on NBC's “The Tonight Show with Jay Leno,” preferring a national audience of almost 6 million viewers over the few hundred who typically attend events in Iowa.

Huckabee appeared at two rallies in Iowa before leaving for Leno's show in California, but Romney criticized him for leaving the state. “He's more focused on the caucus in Los Angeles than the caucus in Iowa,” Romney said.

The candidates' pace was quickened by the realization that what happens in Iowa is likely to have a major impact on their ability to raise funds and continue their campaigns.

For all hopefuls, the priority is not to necessarily win Iowa, but to do well enough to live to fight another day.

“There are basically three tickets out of Iowa,” said Dennis Goldford, a political science professor at Drake University in Des Moines. “If Romney overtakes Huckabee, that will be a big story. If McCain or Thompson comes in third, that will be a big story.”

Romney staked his claim to Iowa early in 2007, spending freely on TV ads and on building his campaign organization.

The state appeared to be his for the taking until the breakthrough of Huckabee, an affable former Baptist minister who appeals to Iowa's influential evangelical Christians but wallowed in low single digits in the polls until late fall.

Romney launched a ferocious ad assault on Huckabee's record in Arkansas, accusing the former governor of being fiscally reckless and soft on crime and illegal immigration.

At campaign appearances, Huckabee challenged Romney's credibility and trustworthiness because of the former Massachusetts governor's changes of position on abortion rights, gay rights and gun control.

Analysts say the caucus electorate has remained unsettled to the very end. That volatility has been evident in the nightly tracking polls being done by pollster John Zogby.

“I'm seeing a convergence on the Democratic side into a bona fide three-way tie,” he said. That was underscored when Zogby pushed supporters of the weaker candidates to name their second choices. In the Democratic caucuses, supporters of any candidate who cannot muster at least 15 percent at each caucus can and usually do switch to a more popular candidate.

In Zogby's poll after second choices are counted, Clinton had 33.7 percent, Obama had 33.7 and Edwards had 32.5. “I have never seen a three-way race this tight,” he said.

The Web site Real Clear Politics, which posts daily averages of publicly available polls, also found a statistical three-way tie: 29 percent for Obama, 28.6 percent for Clinton and 26 percent for Edwards. Trailing far behind were New Mexico Gov. Bill Richardson with 5 percent and Sen. Joe Biden of Delaware, 4.5 percent.

The Republican race is no less muddled.

Real Clear Politics showed Huckabee with 29 percent to Romney's 28.3 percent. There was a statistical tie for third place between McCain at 12.8 percent and Thompson at 11.8 percent. Rep. Ron Paul of Texas and former New York Mayor Rudy Giuliani remained in striking distance of third place with 7.5 percent and 6 percent, respectively.

In Zogby's polling, Huckabee and Romney were dropping slightly, with their supporters going to McCain and Thompson. McCain yesterday received a boost from recent polls showing him in a statistical tie for the top spot nationally and in New Hampshire, which holds its primary election Tuesday.

Analysts made comparisons between this Republican race and the Democratic contest four years ago, which appeared to be a battle between Howard Dean and Dick Gephardt. Both damaged each other with repeated attack ads, helping Sen. John Kerry of Massachusetts win Iowa by 6 percentage points over Edwards and start his march toward the nomination.

“This may be a race similar to the Democrats last time where there really is no national front-runner,” said Bruce Nesmith, a political science professor at Coe College in Cedar Rapids. “That may give whoever wins here a tremendous boost, similar to what it did to John Kerry four years ago.”

Among the Republicans, Nesmith said, “Giuliani, McCain and to a certain degree Thompson have sort of conceded Iowa to Huckabee and Romney. If Huckabee wins, the person who takes it on the chin is Romney, no matter how well he finishes in second.”

With 29 states voting between now and Feb. 5, Romney and Giuliani are pursuing different strategies to the Republican nomination.

Romney is investing heavily in the early voting states of Iowa, New Hampshire and South Carolina, while Giuliani is making a minimal effort in the early states while hoping to score big in Florida in late January and California, New York and New Jersey on Feb. 5.

The Iowa caucuses are not elections in the traditional sense, making them even more difficult to predict. They are political party meetings at schools, churches or people's homes that can last several hours.

A Des Moines Register poll found that 60 percent of the Democrats and 40 percent of the Republicans who said they were likely to go would be doing so for the first time.

One such person is Marna Falcone, who was in the mortgage business until her job fell victim to the sub-prime credit crisis. Born and raised in Iowa, she plans to attend her first caucus today.

But that's all she's decided.

As a registered independent, Falcone can declare her affiliation with either party when she arrives at the caucus site.

“I haven't even decided which one to go to,” she said in an interview this week. “I like Huckabee. But I also like a couple of the Democrats: Hillary Clinton and John Edwards.”