Secret Billionares summit was held in manhatten.

THE secret is out on a clandestine billionaires' summit held in Manhattan earlier this month, when some of the wealthiest Americans met behind closed doors to plot strategies for weathering the economic downturn and coordinating their global philanthropic efforts.

Bill Gates and Warren Buffett organized the hush-hush huddle held in a Rockefeller University conference room on the Upper East Side with Mayor Bloomberg, George Soros, Oprah Winfrey, Eli Broad, Ted Turner, David Rockefeller Sr. and David Rockefeller Jr., among others.

Topic No. 1 during the May 5 conclave was which of the moguls' favorite causes -- such as disease control or government reform -- needed extra help during the downturn. They also sought ways to encourage the common man to keep making small-change donations, an aide to one participant said. IrishCentral.com, which first reported on the powwow, said Gates and Buffett also solicited views on how the group should respond to the global economic climate.

CNN founder Turner, a staunch conservationist and United Nations supporter, was reportedly the most outspoken -- he's known as Capt. Outrageous and the Mouth of the South -- while talk-show queen Oprah was in "listening mode."

In all, the attendees have donated a collective $70 billion since 1996, according to the Chronicle of Philanthropy.

Bloomberg, worth an estimated $20 billion, yesterday declined to discuss specifics of the meeting. "I meet periodically with lots of my friends who are philanthropic," he said. "All my friends are philanthropic or they probably wouldn't be my friends . . . There are meetings all over this city and there are some very powerful people in this city."