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As summer turned to fall, a chilly wind was blowing in New Hampshire for Hillary Rodham Clinton: A new poll on Thursday showed Senator Bernie Sanders of Vermont surging ahead of Mrs. Clinton with 46 percent of the vote to 30 percent for her.

The poll, by the University of New Hampshire for CNN and WMUR, found that even if Vice President Joseph R. Biden Jr. entered the race, he would not garner nearly enough support to win or change the dynamic of the race. Just 14 percent of likely Democratic primary voters said they would back Mr. Biden. If Mr. Biden does not run, the poll suggests that more of his supporters would back Mrs. Clinton, but not enough to put her over the top.

There does not appear to be a groundswell of support in New Hampshire for a Biden run — 37 percent said he should run, but 32 percent said he should not.

Mr. Sanders has a strong lead over Mrs. Clinton among men and is nearly tied with her for support among women. He also bests her in personal traits: Voters view her as the least honest and least likable of the major candidates.

Voters are nearly evenly split over who they think will win the New Hampshire primary — a question that pollsters say often gives a good feel for the dynamics of a race.

Still, more of those polled said they thought Mrs. Clinton would win the general election in November (51 percent said she would win, while 19 percent said Mr. Sanders would).

And more people said they thought she had the right experience to be president — 44 percent, compared with 18 percent who said Mr. Sanders had it; 23 percent said the vice president had the right experience.

The poll sampled the views of 314 likely Democratic primary voters between Sept. 17 and 23 and had a margin of sampling error of plus or minus six percentage points.