DES MOINES, Iowa (Reuters) - Democrat Barack Obama pulled even with Hillary Clinton in Iowa, with John Edwards close behind, in a tightening three-way race one day before the first presidential nominating contest, according to a Reuters/C-SPAN/Zogby poll released on Wednesday.
Obama gained two points overnight and Clinton lost two points to deadlock at 28 percent among Democrats in Iowa, with Edwards in a statistical dead heat behind them at 26 percent. No other Democrat registered in double digits.
The Republican race in Iowa also tightened, with former Arkansas Gov. Mike Huckabee's lead over former Massachusetts Gov. Mitt Romney sliced to two points, 28 percent to 26 percent.
Arizona Sen. John McCain and former Tennessee Sen. Fred Thompson were tied for third at 12 percent.
"Both races are getting tighter as the caucuses get closer," pollster John Zogby said.
The rolling poll of 933 likely Democratic caucus-goers and 907 likely Republican caucus-goers was taken Saturday through Tuesday and has a margin of error of 3.3 percentage points for each party.
Obama, Clinton, and Edwards have battled for the top Democratic spot for months in Iowa, which on Thursday kicks off the state-by-state battle to choose Republican and Democratic candidates for the November presidential election.
Obama, an Illinois senator, made small gains among independents and solidified his strength among younger voters. Clinton, a New York senator and former first lady, maintained her strong lead among older voters.
Edwards, a former North Carolina senator, remained the top second choice of Democrats. A candidate must have 15 percent support in each precinct to be viable or their supporters can switch to another candidate.
When second-choice voters from second-tier candidates are re-allocated to the top three, the Democratic race is a virtual three-way tie, Zogby said.
"We seem to have a convergence of the three top Democrats," he said. "It just keeps getting closer and closer."
New Mexico Gov. Bill Richardson gained two points to claim fourth place with 7 percent and Delaware Sen. Joseph Biden was at 4 percent. Delaware Sen. Chris Dodd and Ohio Rep. Dennis Kucinich were at 1 percent each.
About 7 percent of Republicans and 6 percent of Democrats remain undecided.
In the Republican race, Huckabee slipped two points after criticism from Romney over his record as Arkansas governor. One day of polling came after Huckabee's heavily publicized news conference on Monday, when he announced he would not air a new attack ad against Romney, then showed it to reporters.
"Huckabee's numbers are clearly going down, but Romney's are not going up," Zogby said.
The biggest Republican gains were by Thompson, who pulled into a third-place tie with McCain at 12 percent after gaining two points, and Texas Rep. Ron Paul, who jumped two points to 9 percent.
Thompson has been pulling support from voters who identify themselves as "very" conservative and born-again Christians -- key constituencies for Huckabee, a Baptist minister whose rise has been fueled by backing from religious and social conservatives.
"Thompson seems to be benefiting from conservatives looking for a candidate," Zogby said.
Former New York Mayor Rudy Giuliani, who has focused on later states and largely bypassed Iowa, was at 7 percent in the Republican race and California Rep. Duncan Hunter was at 1 percent.
The rolling tracking poll will continue each day through the Iowa caucus on Thursday. In a rolling poll, the most recent day's results are added while the oldest day's results are dropped in order to track changing momentum.