WASHINGTON (Reuters) - Barack Obama has erased a once substantial deficit to climb into a virtual tie with Hillary Clinton in the Democratic presidential race, according to a Reuters/Zogby poll released on Wednesday.
Among Republicans, John McCain charged to the front of a shifting presidential field, shooting past Mike Huckabee and a fading Rudy Giuliani as the opening contests of the 2008 White House campaign dramatically reshaped the races in both parties.
Heading into potentially crucial contests in Nevada, South Carolina and Florida, the campaign to choose candidates for the November election to succeed President George W. Bush has shown deep volatility.
Wins in Iowa by Obama, an Illinois senator, and Huckabee, a former Arkansas governor, gave both candidates jolts of momentum in the race.
But the momentum was short-lived as New Hampshire comeback wins by Clinton, a New York senator, and McCain, an Arizona senator, five days later set up potentially lengthy Democratic and Republican nominating battles.
"This the definition of a hard-fought race," pollster John Zogby said.
The poll was taken on Thursday and Friday, before Tuesday's Michigan Republican primary, in which former Massachusetts Gov. Mitt Romney beat McCain by 39 percent to 30 percent. Huckabee came in third with 16 percent.
Democrats also held a primary in Michigan but a dispute over the date of the vote led the national party to strip the state of its delegates to this summer's presidential nominating convention, making the contest meaningless.
The survey found only marginal support for a potential independent candidacy by New York Mayor Michael Bloomberg, who has flirted with the idea of a third-party run for the White House while officially denying any interest.
Clinton, a former first lady who would be the first woman U.S. president, held a 21-point edge over Obama in October. He cut that to 8 points by last month, and the new survey gave her a 39 percent to 38 percent edge.
Her 1-point lead was well within the poll's margin of error of 4.7 percentage points.
Obama, who would be the first black U.S. president, and Clinton were essentially deadlocked among a variety of groups, including men, women, Democrats and independents. Obama led substantially, 65 percent to 15 percent, among black voters.
Obama barely led among voters under age 24, a substantial drop in support from last month, but led Clinton among voters aged 55 to 69, normally one of her strengths.
"This is an unbelievably close race at almost every level," Zogby said.
Former North Carolina Sen. John Edwards, the only other major Democratic contender still in the race, was a distant third at 9 percent in the national poll.
Among Republicans, McCain led Huckabee by 28 percent to 23 percent as the pair took advantage of their wins in the first two nominating contests.
It was a 16-point jump for McCain from last month and a one-point increase for Huckabee, who had already begun his climb by mid-December.
"Clearly this is a post-Iowa, post-New Hampshire bounce," Zogby said.
Huckabee, an ordained Baptist minister whose rise has been fueled by support from religious conservatives, led 34 percent to 22 percent among those who described themselves as "born-agains."
McCain led among independents 45 percent to 13 percent and among moderates by 53 percent to 13 percent, while McCain and Huckabee tied among Republican voters.
In third place was former Tennessee Sen. Fred Thompson at 14 percent, with former Massachusetts Gov. Mitt Romney at 13 percent.
All of them shot past Giuliani, the leader in national polls for much of the year. His support has been steadily dropping, from 29 percent in November to 23 percent last month and just 9 percent this month.
The slide has raised questions about Giuliani's strategy of bypassing the early voting states to concentrate on Florida's January 29 primary and the February 5 "Super Tuesday" round of 22 state contests.
"This is what happens in a sequential process when you don't win," Zogby said. "You have to win somewhere and he hasn't."
The national survey had Republican Rep. Ron Paul at 4 percent and California Rep. Duncan Hunter at less than 1 percent.
Asked about Bloomberg, about 60 percent said it was very unlikely they would support the New York mayor, with another 16 percent saying it was somewhat unlikely. Just 4 percent said it was very likely they would back him, with 15 percent saying it was somewhat likely.
The poll surveyed 459 likely Democratic primary voters and 427 likely Republican primary voters, with a margin of error of plus or minus 4.7 percentage points for Democrats and 4.8 percentage points for Republicans.
(Editing by David Wiessler)
(For more about the U.S. political campaign, visit Reuters "Tales from the Trail: 2008" online at blogs.reuters.com/trail08/)