MANCHESTER, N.H. Senator McCain placed his revived Republican presidential campaign on the line against a weakened but determined Mitt Romney as New Hampshire primary voters came out in large numbers today. Senator Obama declared Americans were ready to “cast aside cynicism” as he looked for a convincing win in the Democratic contest.

Weather was spring-like and participation brisk, although it remained to be seen whether New Hampshire would match the record-busting turnout of the Iowa caucuses won by Mr. Obama and Michael Huckabee only five days earlier. Republicans, their national race for the nomination tangled, watched a New Hampshire contest unfold between Messrs. McCain and Romney at the top of their field, polls indicating Mr. McCain had an edge but no clearcut advantage.

Supporters mobbed an upbeat Mr. McCain at a Nashua polling station, making it hard for him to reach voters as they filed inside. Noting he outpolled rivals in two tiny northern hamlets that voted before the rest of the state, Mr. McCain cracked: “It has all the earmarks of a landslide, with the Dixville Notch vote.” Mr. Romney boldly predicted: “The Republicans will vote for me. The independents will get behind me.”

Senator Clinton promised a daylong blitz to get her supporters out, even as those closest to her acknowledged the difficulty of trying to counter Mr. Obama’s momentum so soon after the Iowa caucuses.

Mr. Obama spoke at Dartmouth College — his relatives in Kenya gathered outside by radio, waiting to hear New Hampshire returns.

“Today you can make your voice heard — you can insist that change will come,” Mr. Obama told the crowd. “The American people have decided for the first time in a very long time to cast aside cynicism, to cast aside fear, to cast aside doubts.”

Looking back at his Iowa victory, the man who would be the first black president said: “The state was not, according to the experts, designed for me. There were not a lot of people who look like me in Iowa.”

At Brookside Congregational Church in Manchester, 50 voters lined up before dawn and people waited in their cars for a parking space after doors opened. When Mr. Huckabee passed a fellow GOP candidate, Mayor Giuliani, outside, Mr. Huckabee jokingly asked for his vote. “We get along beautifully on the trail,” Mr. Huckabee said.

Mr. Giuliani waved off a question about his decline in polls, pointing to the church and saying, “The only poll I’m interested in is the one that goes on inside there.” That wasn’t exactly so. At his New Hampshire headquarters, he asserted that opinion polls in some 15 states find him on top.

The nation’s first primary offered Mr. Obama a chance to become the clear favorite for the Democratic presidential nomination while Messrs. McCain and Romney competed head to head in a Republican race that seemed bound to sink the aspirations of one of them.

Rooting from distant sidelines, Mr. Obama’s Kenyan relatives sat in plastic chairs at the end of a dusty road lined with mango and mimosa trees, listening to the radio. The Democrat’s uncle, Said Obama, commented that his nephew “has proved to be a beacon of hope here and shown that even in difficult circumstances you can make it to the highest height of achievement with just determination and hard work.”

Kogelo, the western Kenyan home village of Barack Obama’s father, has been spared the violence that has erupted elsewhere following a disputed presidential election. Mr. Obama called the Kenyan opposition leader, Raila Odinga, yesterday and was expected to do the same today with President Kibaki to express concern about the election outcome.

President Clinton dampened expectations for his wife, saying the unusually short stretch between Iowa and New Hampshire presented little chance to counter Mr. Obama’s bounce.

Boisterous supporters chanted Mr. Edwards’s name as he left a polling site in Manchester. The former senator from North Carolina hoped Mrs. Clinton would be sufficiently weakened today to give him an opening.

He said voters will give Mr. Obama a hard look going forward, a point amplified by Elizabeth Edwards. “With all of the sort of gauziness, it’s sort of like a first date in a lot of ways with these candidates,” she said. “At some point people recognize that ‘I’m not going on a first date with this fellow, I’m marrying them.'”

Paradoxically, the struggle for primacy in the Democratic and Republican campaigns was, to an outsized degree, in the hands of independents who make up a large share of the voters here and by definition are not loyal to either party.

Mrs. Clinton and her daughter Chelsea poured coffee for voters and a police officer at a Manchester elementary school before dawn. They were greeted by a dozen voters and twice as many supporters outside. “We’re going to work all day to get the vote out,” she said.

Her next stop was at a polling place in a Nashua high school, where pupils who had just arrived by bus screamed with excitement and enveloped her. She worked her way to a group of 50 supporters, some hugging her as she moved down the line greeting them.

At a school in a working class Manchester neighborhood, Anna and Adam Helbling looked beyond the passions of the moment to the Democrat they think could win in the fall, and voted for Mr. Obama. “I really wanted to vote for Hillary, but I think Obama has a really good chance against a Republican rival,” Mrs. Helbling said.

Mr. Huckabee wooed an independent voter, Joe Legay, by pouring him coffee from a doughnut-shop container. “I’m independent so I have to be quiet,” Mr. Legay said when Mr. Huckabee asked how he would vote. He said later he voted for Mr. Obama.

Kathy Nadeau, 49, a property manager, backed Mrs. Clinton because of her experience. “Hillary has done a good job in Washington,” she said, “and I think she can bail us out.”

The high number of independents presented an opportunity for Mr. McCain, a GOP iconoclast who won New Hampshire against establishment pick George W. Bush in 2000, and for Mr. Obama, pressing hard to build a constituency broader than his party. But it also was a complication because they were dipping into the same nonaligned pool.

Even so, polls indicated Mr. Obama had pulled ahead of Mrs. Clinton as she fought to write a “comeback kid” story to rival that of her husband in 1992.

In a northern New Hampshire hamlet tradition, voters of Dixville Notch and Hart’s Location cast the first 46 ballots of the primary season — half for Democrats and half for Republicans — at midnight, hours before polls began opening elsewhere at 6 a.m. Polls close at 8 p.m. Messrs. Obama and McCain came out on top.

The gym at Dartmouth was only about two-thirds full, in contrast with Mr. Obama’s packed events over the last few days. A young woman near the front of the crowd passed out while he was speaking, and he stopped his speech for a full nine minutes, staring down with his arms crossed, until she was taken out on a stretcher, alert and talking.

Mr. McCain held a statistically insignificant lead over Mr. Romney in late polls. Mr. Obama had a clear advantage over Mrs. Clinton in surveys and Mr. Edwards trailed both, with Governor Richardson of New Mexico in the rear.

Iowa GOP winner Mr. Huckabee campaigned vigorously in New Hampshire in the final days but without expectations of victory. A former Tennessee senator, Fred Thompson, and one-time national poll leader Mr. Giuliani looked to later contests. Mr. Thompson campaigned in South Carolina as New Hampshire voted.