MANCHESTER, N.H. — Her voice quavering, Sen. Hillary Rodham Clinton struggled Monday to avoid a highly damaging second straight defeat in the Democratic presidential race. Republicans John McCain and Mitt Romney scrapped for success on the eve of a New Hampshire primary that neither could afford to lose.

"You're the wave, and I'm riding it," Sen. Barack Obama, the new Democratic front-runner, told several hundred voters who cheered him in 40-degree weather after being turned away from an indoor rally filled to capacity.

Obama has been drawing large, boisterous crowds since he won the Iowa caucus last week, and a spate of pre-primary polls showed him powering to a lead in New Hampshire as well.

Clinton runs second in the surveys, with former Sen. John Edwards of North Carolina third, and the former first lady and her aides seemed to be bracing for another setback.

At one stop, she appeared to struggle with her emotions when asked how she copes with the grind of the campaign — but her words still had bite. "Some of us are ready and some of us are not," she said in remarks aimed at Obama, less than four years removed from the Illinois Legislature.

New Hampshire fairly crawled with candidates, so much so that at one point, McCain's three-bus caravan drove past Rep. Duncan Hunter of California, a long-shot Republican standing on a street corner with two other people waving to cars.

Opinion polls made the Republican race a close one between McCain, the Arizona senator seeking to rebound from last summer's near collapse of his campaign, and Romney, the former governor from next-door Massachusetts.

After sparring over taxes and immigration in weekend debates with McCain and former Arkansas Gov. Mike Huckabee, Romney cast himself as the Republican best able to hold the White House. "I think Barack Obama would be able to do to John McCain exactly what he was able to do to the other senators who were running on the other side," Romney said as he sped his way through a half-dozen events on a final full day of campaigning.

After first declining to predict victory in a state where he had led in surveys for months, Romney exuded confidence by the end of the day. "I'm convinced we're going to win tomorrow," he boasted at a rally for his staff at the campaign's headquarters. He attributed the change of heart to 100,000 telephone calls made by his staff, and his performance in back-to-back nationally televised debates on Saturday and Sunday.