That is ahead of Mr. de Blasio’s pace at this stage in the race during his first run for mayor. He had 294 donors who had given the maximum at the time of the March 2013 filing. However, at that time, Mr. de Blasio was the city’s public advocate, mounting what appeared to be a long-shot campaign for mayor in a crowded field. Now he is the city’s mayor, with much higher expectations of his ability to raise large amounts of money.

It is difficult to make comparisons with other mayoral campaigns, partly because Mr. de Blasio’s predecessor, the billionaire Michael R. Bloomberg, who paid for his own campaigns, served three terms without ever taking campaign donations.

“There’s a lot of churning in donor pools, much more than people have realized,” said Michael J. Malbin, executive director of the Campaign Finance Institute, a nonpartisan research center in Washington, adding that the phenomenon may be greater this year for Mr. de Blasio because he has sought to reach out to more small donors.

“It’s a general rule in politics that people only give after they’re asked, so if he’s shifting his focus maybe he’s asking fewer of the traditional donors,” Mr. Malbin said. “But some of that may be that his base of support had shifted somewhat.”

In an analysis of contributions to the presidential campaigns of George W. Bush, Mr. Malbin found that 30 percent of donors who gave $200 or more in 2000, and a similar percentage of donors who gave the maximum of $1,000, contributed again in 2004. Those are much higher rates than Mr. de Blasio has seen so far, but there are still many months for donors to make contributions.

There are some striking shifts among Mr. de Blasio’s top donors this time, compared with four years ago.

Many former donors in the real estate industry have not contributed to his re-election campaign so far. At least 48 people who gave the maximum to Mr. de Blasio in 2013 and who listed a real estate company as their employer, including developers and brokers, have given nothing this time around. Among them is Mr. de Blasio’s best-funded challenger, the realty sales executive Paul J. Massey, who gave Mr. de Blasio $4,950 in 2013. Mr. Massey is seeking the Republican nomination to oppose Mr. de Blasio in November.

Real estate industry executives said that developers and others had held back donations from Mr. de Blasio’s re-election effort in part because the investigations into his fund-raising had made them leery of the scrutiny large donations could bring. One executive, who asked not to be named so as not to jeopardize relationships with City Hall, said that some also feared that a donation could backfire if city officials felt compelled to act less favorably to big donors with projects requiring city action regarding zoning or other factors, in order to avoid any suggestion of pay to play.