updated 11:00 p.m. ET, Mon., Dec. 31, 2007

Presidential contenders rang in the new year with near-constant campaigning on Monday as a poll showed Democrat Barack Obama and Republican Mike Huckabee leading their rivals with three days remaining before the Iowa caucuses.

Anonymous phone calls and a negative campaign commercial that vanished into thin air also spiced the race, and not even New Year's Eve was off-limits to campaigning.

The poll by the Des Moines Register showed Obama, an Illinois senator, with the support of 32 percent of those surveyed, compared to 25 percent for Sen. Hillary Rodham Clinton of New York and 24 percent for former Sen. John Edwards of North Carolina.

Among Republicans, Huckabee, a former Arkansas governor, had the backing of 32 percent of those surveyed, and former Massachusetts Gov. Mitt Romney had 26 percent.

Other polls have shown far closer races in recent days within both parties, and the leading candidates are engaged in a virtual nonstop round of personal appearances across the state that provides the first test of the race for the White House.

"I'm taking a risk, I know I am," said Huckabee, who previewed an ad sharply critical of rival Mitt Romney during the day after first assuring reporters he would not air it on TV.

The three top Democratic rivals campaigned in far more traditional fashion, and Obama, Edwards and Clinton combined for more than a dozen appearances before time ran out on 2007. Clinton got the distinction for the last event of the year -- in downtown Des Moines with her husband, the former president.

"We want our government back, we want our democracy back," Edwards told an audience in Storm Lake. Locked in a three-way race, the former North Carolina senator claimed late momentum for a campaign built around his pledge to fight special interests in Washington.

Clinton, a former first lady bidding to become the first female president, seemed primed to counter. "I submit to you there isn't anybody running who's taken on more special interests and taken on more incoming fire and survived them than I have," she told a crowd in Keokuk.

Without mentioning Edwards by name, she appeared to gently mock the fired-up speaking style he uses to deliver his populist pledge. "It's not something you have to do by yelling and screaming," she said. "Save your energy."

Obama stuck doggedly to the campaign pitch that has made him the most serious black presidential candidate in history. "You can't afford to settle for the same old politics," he told a crowd in Perry.

The poll said Obama was benefiting handsomely from an influx of first-time caucus-goers. If so, that meant his finish in the state would hinge to an extraordinary degree on the ability of his organization to turn out supporters.

In yet another sign of uncertainty, nearly a third of those polled said they could still change their minds.

In a gesture that reflected the hand-to-hand nature of the political struggle, his campaign arranged to have a former Clinton supporter, Marlin Eineke, introduce Obama to the crowd. The political convert said he was attracted to Obama's positive campaign.

Obama's aides took steps to stress their man's strength in the states that vote after Iowa, and against Republicans in the fall campaign. But like everything else in the race for the White House, all of that remains to be recalculated after Iowa's precinct caucuses on Thursday.

New Hampshire holds its first-in-the-nation primary five days after Iowa's caucuses, and if history is a guide the roster of candidates will be far slimmer by then. Already, Democrats Chris Dodd and Joseph Biden have spoken about dropping out if they fail to meet their expectations in Iowa.

With three days remaining until the caucuses, several Democratic voters reported receiving anonymous telephone calls from self-proclaimed pollsters spreading unflattering information.

Some calls said Obama's health plan would leave millions uninsured. Others said Edwards' plans for a troop withdrawal from Iraq were dangerous or that Clinton would lead the party to defeat in the fall.

One Democrat, Michael Hancock of Coralville, said he had received an automated call reminding him that an important college football game would be televised Thursday night at the same time the caucuses were held.

He said he promptly hung up his phone before concluding it was a "transparent attempt to depress turnout from some people." Neighboring Kansas plays in the Orange Bowl Thursday night.

No group has taken responsibility for any of the calls.

While Democrats were in a tight three-way race in Iowa, the Republican contest came down to a two-way struggle between Huckabee and Romney.

Romney, the former Republican governor of Massachusetts, used his personal wealth to jump out to a sizable early lead in both Iowa and New Hampshire. Huckabee's support among evangelical Christians allowed him to overtake Romney in surveys in recent weeks, although he has more lately fallen back under the weight of criticism of his record as governor of Arkansas as well as his own campaign missteps.

Stepping before more than a dozen television cameras, Huckabee first swore off negative ads in the Iowa race, then previewed a commercial in which he was seen saying of his rival: "If a man's dishonest to obtain a job, he'll be dishonest on the job. Iowans deserve better."

He acknowledged the risk to his campaign of allowing Romney's critical commercials to go unanswered, but said of his own supporters: "If they abandon us now because we are not going negative I would be surprised."

"If you gain the whole world and lose your soul, what have you profited?" asked the Baptist preacher-politician.

Huckabee is trying to outflank Romney in their race for primacy in Iowa -- and in the national polls."

He told reporters one of the reasons he originally intended to launch a negative commercial was because Romney had assailed a third candidate, Sen. John McCain. McCain has made a relatively modest effort in Iowa, and Huckabee could benefit in the campaign's final few days if he could peel away some Republicans who had been leaning toward the Arizona senator.

Huckabee also suggested a two-way debate in the final two days that would allow Romney and him to share a stage.

Romney had no immediate response to that as he made his final campaign rounds of 2007.

He launched an upbeat new commercial that said it was "time to turn around Washington."

At the same time, he was freshly critical of Huckabee's record as governor, saying voters would be put off by his rival's position on immigration and the pardons he had granted while governor.

McCain had New Hampshire to himself, and he defended himself against Romney's ad that points out he opposed President Bush's tax cut in 2001. "There was no restraint in spending" to accompany the cuts, he said.