President Obama narrowly leads Mitt Romney in three key swing states — New Hampshire, Nevada and North Carolina, according to an NBC News-Wall Street Journal-Marist poll released Friday.

Obama’s biggest lead is in New Hampshire, where he takes 51 percent support, over Romney at 44. That’s greater than the 2.5-point lead the president has in the RealClearPolitics average of polls for that state.

Romney is within the poll’s margin of error in the other two states. Obama leads 49 percent to 47 in Nevada and 48 percent to 46 in North Carolina.

The RCP average of polls shows Obama with a 4-point lead in Nevada and a 1-point lead in North Carolina.

NBC News-Wall Street Journal-Marist has polled nine swing states in September — Colorado, Florida, Iowa, Nevada, New Hampshire, North Carolina, Ohio, Virginia and Wisconsin — and Obama has leads ranging from 2 to 8 points in all of them.

Those are the bulk of the 12 swing states former President George Bush won in 2004 but Obama won in 2008, and they’ll be critical in determining the outcome of the 2012 election.

The president’s leads in New Hampshire, Nevada and North Carolina are buoyed by a persistent gender gap. While Romney has small leads among male voters in those states, Obama leads among female voters by 20 points in New Hampshire, 16 in North Carolina and 11 in Nevada.

Obama is also helped by improving views among voters on the economy and direction of the country. The two candidates are essentially tied in all three states on who is better equipped to handle the economy.

Romney continues to be dogged by a low favorability rating. The only state where he is viewed more positively than negatively is North Carolina.

Obama’s lead in the swing-state polling comes as the president has also seen a boost in his polling numbers nationally. Obama stretched his lead over Romney to 50 percent to 44 in Wednesday’s Gallup daily tracking poll.

The NBC News-Journal-Marist polls of likely voters were conducted between Sept. 23 and Sept. 25 and have a 3.1 percent margin of error.