(CNN) -- With less than a week before Election Day, polls released Thursday indicated a narrow edge for President Barack Obama in Iowa, New Hampshire and Wisconsin, three states that are being fiercely contested in the final stretch of the campaign.
In Iowa, Obama was at 50% among likely voters, and Romney at 44%, according to the NBC News/Wall Street Journal/Marist poll. That's slightly tighter than earlier in October, though the result Thursday was just outside the poll's sampling error of plus or minus 2.9 percentage points. A poll released Wednesday indicated a much tighter race in the Hawkeye State - the University of Iowa survey had Obama at 42.7% and Romney at 41%.
Obama's lead in Iowa was bolstered by high levels of early support. A total of 45% of the sample had already cast ballots, or said they were planning to vote before November 6. Among those people, Obama was leading Romney 62%-35%. But among respondents who said they'd vote on Election Day, Romney had the edge, topping Obama 55%-35%.
"President Obama's lead in Iowa is due to those who have voted early or plan to do so, including many independents," said Dr. Lee M. Miringoff, Director of The Marist College Institute for Public Opinion. "Obama has a 21 point lead among Independent voters who plan to cast an early ballot while Romney is up 9 points among independents who plan to vote on Election Day."
In New Hampshire, the race was much closer. Forty-nine percent of likely voters in the Granite State back Obama, compared to 47% who support Romney. The two point margin was well within the poll's sampling error, and was tighter than an NBC/WSJ/Marist poll that was conducted toward the end of September. The earlier survey had Obama at 51% and Romney at 44%.
The New Hampshire survey released Thursday is the first live operation, non-partisan poll of the state conducted after the final presidential debate on October 22. Polls taken immediately before that showdown indicated a volatile race: an American Research Group survey taken October 9-11 showed Romney with a two point edge over Obama, 49%-47%, but a UNH poll taken October 17-21 showed Obama with the edge, leading Romney 49%-41%.
There were far fewer early voters in the New Hampshire sample, since that state offers only absentee voting by mail, rather than in-person options.
"The battle for New Hampshire's four electoral votes has gotten very close," Miringoff said. "The president is not getting anywhere near what he got four years ago when he carried the state by nine points."
A third NBC/WSJ/Marist poll, in Wisconsin, had Obama at 49% and Romney at 46%, within the sampling error. That's a closer race than was shown in a survey released Wednesday from The Marquette University Law School, which indicated 51% of likely Wisconsin voters backing the president while 43% support Romney.
Of the 25% of respondents who said they had already voted, or planned to vote early, Obama was ahead of Romney 59%-39%. But the GOP nominee led 50%-45%.
"President Obama is advantaged by voters who plan to vote early," Miringoff said. "But, Romney benefits from greater enthusiasm among his supporters."
Obama and Romney are closely matched on who would best handle the economy, which voters consistently rate at their top issue heading into the election. Romney held a slight edge on that question in New Hampshire, but in Iowa and Wisconsin the two candidates were tied.
The NBC/WSJ/Marist polls were taken by telephone from October 28-29, from 1,142 voters in Iowa, 1,013 voters in New Hampshire and 1,065 voters in Wisconsin. The sampling error was 2.9 percentage points in Iowa, 3.1 percentage points in New Hampshire and 3.0 percentage points in Wisconsin.