LEBANON, N.H. -- Voters are expected to turn out in record numbers today for New Hampshire's first-in-the nation presidential primary, potentially delivering victories to Sen. Barack Obama of Illinois and Sen. John McCain of Arizona, who both trailed in polls throughout the last year but have gained strong momentum in recent days.

Mr. Obama has opened up a double-digit lead in several surveys over fellow Democratic Sen. Hillary Rodham Clinton of New York since last week, when he became the first black candidate to win the Iowa caucuses.

"I am fired up," he told more than 700 people packed into the Lebanon Opera House, while hundreds gathered outside on the town square to hear him on a speaker system. "We've already changed the political landscape."

On the Republican side, Mr. McCain, the victor in New Hampshire eight years ago, holds a slight but steady edge over former Massachusetts Gov. Mitt Romney, who has invested millions of dollars more than any other GOP candidate on advertising and a ground organization in the state.

"With your help, in the next 24 hours we will win this primary," Mr. McCain said before several hundred supporters at Dartmouth College's Hopkins Center in Hanover.

A Marist College poll released yesterday said Mr. Obama was "positioned to win," with a 36 percent-to-28 percent lead over the former first lady among likely voters in the Democratic presidential primary. Former North Carolina Sen. John Edwards received support from 22 percent of likely Democratic primary voters.

Mr. McCain led Mr. Romney by 35 percent to 31 percent in the same poll. Former Arkansas Gov. Mike Huckabee, who won Iowa's Republican caucuses, was at 13 percent.

Presidential hopefuls crisscrossed the Granite State yesterday, holding dozens of events in school gymnasiums and meeting halls, as they tried to make one final sales pitch to voters. Behind the scenes, campaign staffers and volunteers launched their get-out-the-vote operations, calling thousands of potential supporters.

"It's basically just organization at this stage," said Marshall Cobleigh, a former speaker of the New Hampshire House of Representatives. "I've gotten two or three calls from candidates already."

In Portsmouth, the strain of Mrs. Clinton's recent decline seemed to be taking a toll as she held a meeting over coffee with undecided voters. A sympathetic voter asked her how she keeps going.

"It's not easy, it's not easy," she replied. "And I couldn't do it if I just didn't, you know, passionately believe it was the right thing to do," she said, her voice catching. "You know, I have so many opportunities from this country, I just don't want to see us fall backwards. ...This is very personal for me. It's not just political. ..."

But Mrs. Clinton also went on the offensive, questioning the sincerity of Mr. Obama's message of change and his preparedness for the highest office in the nation. Interviewed on ABC's "Good Morning America," she pointed out that Mr. Obama has portrayed himself as being outside the influence of special interests, yet picked a New Hampshire lobbyist to co-chair his state campaign. She also accused him of changing positions on issues, even though he criticizes other candidates for the same thing.

"All of a sudden you start to ask yourself, Wait a minute. I mean, what is the substance here?" she said. "As famously was said years ago, where's the beef? You know, where is the reality?"

Philip Harold, a Robert Morris University assistant professor of political science, said Mrs. Clinton -- once called the "inevitable" Democratic nominee by many pundits -- was showing signs of weakness. "She just sounds like she's on the ropes," said Mr. Harold, who will teach a class on the 2008 election next fall.

During his appearance in Lebanon, Mr. Obama never mentioned Mrs. Clinton by name, instead referring to her only as an "opponent," a standard move by a frontrunner.

"A few days ago in the debate, one of my opponents said 'Oh, stop giving people false hopes about what we can accomplish,' " Mr. Obama told the crowd. "False hopes? There's no such thing. This country was built on hope."

He noted that, in the days since Iowa's caucuses, candidates in both parties have started echoing his "change" theme.

That's especially true with Mr. Romney, who told reporters that Mr. McCain's decades of Washington experience would make him a weaker candidate against Mr. Obama in the November general election.

"I think Republican voters, who, like myself, were virtually certain that Hillary Clinton would be the nominee have now begun to think Hillary Clinton may not be the nominee; it may well be Barack Obama," he said. "And if they think who can post up against Barack in these debates and in the message that's taken to Washington, they're going to recognize that a long-serving U.S. senator is not the best match-up."

Mr. McCain, a former Navy pilot who was a prisoner in Hanoi during the Vietnam War, spoke yesterday of his long years working on national security issues. He reminded supporters that he had called for a larger number of U.S. troops to help pacify Iraq long before President Bush launched last year's "surge," which has been credited with leading to a significant reduction in violence.

"Everybody talks about change," he said. "I'm glad to be part of the biggest change that saves I don't know how many brave American lives."

He also took a shot at Mr. Romney's heavy spending in the race: "You can't buy an election in the state of New Hampshire. You've got to go out and earn the people's respect, and then you earn their vote."

Mr. Edwards kept pushing fiery populist rhetoric on the campaign trail, telling supporters, "We can't let insurance companies and oil companies and drug companies keep running this country."

Mr. Edwards portrayed Mrs. Clinton as being too close to those groups. He hopes that today's primary could seriously damage her campaign and propel him into a two-way race with Mr. Obama.

Mr. Huckabee is hoping that a surprisingly strong third-place finish in New Hampshire -- a state with fewer evangelicals to support the former Baptist preacher than Iowa offered him -- could provide a national boost. Two other GOP contenders -- former Tennessee Sen. Fred D. Thompson and former New York City Mayor Rudolph W. Giuliani -- have campaigned much less frequently in New England.

Mr. Thompson is putting his focus on South Carolina's Jan. 19 Republican primary, while Mr. Giuliani thinks he can post a strong showing Jan. 29 in Florida.

Mr. Cobleigh, who once advised the Giuliani campaign, said the New Yorker's approach likely would backfire. "This is not the way you win New Hampshire. He'd be lucky if he beats Ron Paul for fourth place," he said, referring to the libertarian Texas congressman also seeking the GOP nomination.