A woman's tearful plea to Democratic presidential candidate Barack Obama to end the Iraq war momentarily caught him off guard Friday at a New Hampshire town hall meeting.

The Illinois senator vowed to end the unpopular conflict if elected, a position that later earned him thunderous applause during a 5,800-person rally in Boston.

Obama fielded questions about health care, gun control and energy during a midday appearance before some 200 people at a Nashua senior center. The residents politely applauded, and then Jean Serino of Hudson told the candidate her nephew was heading to Iraq to serve.

"I can't breathe," she said, her voice breaking with sobs. "I want to know, when am I going to be able to breathe? Are you going to get us the hell out of there? Promise us you will get us out of there. That's the most important thing."

The crowd's applause as she finished gave Obama time to compose an answer.

"I can only imagine how you feel, as a father and as a parent," he said. "I don't go to a single town-hall meeting where I don't meet a mother or father who either is seeing a loved one go over there or has already lost someone, or has a loved one who has come back injured.

"So I make a solemn pledge to you, as president we will be out of Iraq," Obama said to loud applause.

Democratic presidential contenders have repeatedly faced questions from voters about the four-year-old war during stops in New Hampshire. New York Sen. Hillary Rodham Clinton has dealt with pointed questions about why she won't apologize for her 2002 vote authorizing President Bush to use military force to oust Saddam Hussein.

A recent poll showed that ending the war is the top priority for New Hampshire voters when considering presidential candidates.

Obama reiterated his plan to remove troops by March 31, 2008, similar to a plan passed by Congress that President Bush has vowed to veto.

Democrats don't have enough votes to override the veto. Without mentioning them by name, Obama criticized New Hampshire Sens. Judd Gregg and John Sununu, both Republicans who voted against the troop withdrawal deadline.

"There are two New Hampshire senators who have not made a commitment," he said, "and the power is in their hands."

Obama also reiterated his criticism of the system for background checks for gun purchases after the massacre at Virginia Tech.

"We're still selling handguns to crazy people," Obama said. "We're supposed to have a system that these people are screened out. What's clear is the background check system in this case failed entirely."

Seung-Hui Cho, the gunman who shot 32 people at Virginia Tech on Monday before killing himself, had a history of mental health problems but still was able to buy two guns.

At a campaign rally at Boston University on Friday night, Obama challenged a sold-out crowd to abandon doubt and get involved in the campaign.

"Too much is at stake not to overcome that cynicism," he told a rowdy crowd of mostly college students who donated $23 to attend the New England campaign launch. "If all of you decide this is your campaign and not my campaign, this cannot be stopped."