A few prominent black leaders remain on the fence. Among those leaders is the Rev. Al Sharpton. On Friday, in one sign of how vigorously he is being courted, Bill Clinton called into Mr. Sharpton’s nationally syndicated radio talk show to explain his use of the phrase “fairy tale” in a critique of the Obama campaign this week. The description angered many blacks, but Mr. Clinton said he was referring only to Mr. Obama’s position on Iraq, not his candidacy.

Neither campaign has made firm decisions yet about television advertising and public appearances in the state, which has 5.3 million enrolled Democrats.

Their ranks could be swollen by last-minute registration efforts. Unregistered New Yorkers had until Friday to enroll in order to be eligible to vote Feb. 5.

The New York City Board of Elections said more than 13,000 forms had been filed in the last week alone. In New Hampshire, Mr. Obama fared better among first-time primary voters.

On primary day, 232 of New York’s 281 convention delegates will be in play, 151 of them elected by Congressional district and allotted in proportion to the candidate’s total. Some delegate slots are reserved for public officials and party leaders, and others are assigned by party officials. Representative Anthony D. Weiner, a Clinton supporter who represents parts of Brooklyn and Queens, said the campaign dynamics have energized the Clinton camp, too.

“It’s now clear that her home state is going to play an important role in making her president,” he said. “People are more excited about that than concerned.”

He said he had not discerned any shift to Mr. Obama among Clinton supporters.

At least one has shifted the other way. Neil Barsky, a Manhattan hedge-fund manager who raised money last year for Mr. Obama, said he now favored Mrs. Clinton. “I believe Hillary, while potentially less of a transformational candidate, would make an excellent president and is our best chance of winning,” he said.