Mayor Bloomberg has padded the bank accounts of hundreds of nonprofit organizations throughout the city with a $20 million donation to the Carnegie Corporation and a directive to spread the wealth.

While the donation was made anonymously, a source close to Mr. Bloomberg confirmed yesterday that it came from the mayor, a billionaire whose personal fortune has been estimated at more than $4 billion. The source likewise asked to go unnamed.

The donation also has Mr. Bloomberg’s fingerprints on it. It is the fourth anonymous gift the Carnegie Corporation has received since the mayor took office in 2001.The first two years, the money was given for cultural organizations throughout the city. Last year and this year, the donor asked Carnegie to give the money to social service organizations as well.

“The donor asked that the money go to a mix of small and medium-size organizations deep in the neighborhoods and really blanketing the city,” the vice president of public affairs for the Carnegie Corporation, Susan King, said.

Ms. King refused to confirm or deny the identity of the donor. “The donor has asked us to make these grants,” she said. “In our world, the intent of the donor to remain unnamed is the first principle.”

Carnegie will be issuing the grants soon after the mayor and the City Council agreed to next year’s budget. The money will undoubtedly help shore up budget shortfalls for some groups and come as welcome gravy for others.

The $20 million donation announced yesterday was $5 million more than last year’s gift and $10 million more than those of each the previous two years. According to Ms. King, the money was given at the end of 2004 and will go to 406 groups throughout the city.

The groups, a listing of which is posted on the foundation’s Web site, range from the Staten Island Mental Health Society to the Frank Sinatra Writers Workshop Foundation, Inc.

A group called the Castillo Cultural Center, which has ties to a controversial leader of the Independence Party, Lenora Fulani, was not on the list this year as it had been in the past.

In 2002, the group, which is owned by a nonprofit group founded by Ms. Fulani called the All Stars Project, received money through one of the Carnegie grants attributed to the mayor. At that time, the Carnegie Corporation and the mayor’s office denied that Mr. Bloomberg was attempting to steer money to the cultural center.

Ms. Fulani, whose party has backed Mr. Bloomberg for mayor in 2001 and again this year, has been accused of making anti-Semitic comments and, more recently, refusing to retreat from those remarks.

There did not seem to be any particularly controversial groups on the list of nonprofit recipients released yesterday by Carnegie.

The president of the New York Regional Association of Grantmakers, Michael Seltzer, said he did not have first-hand knowledge of Mr. Bloomberg’s donation. He said, however, that Mr. Bloomberg is the first sitting mayor in the city’s history who is also a philanthropist.

A spokesman for the mayor, Jordan Barowitz, declined to comment on the donation. The mayor’s office has always denied that his donations are meant to curry favor or political support.