By Suzanne Perry

The John D. and Catherine T. MacArthur Foundation will start a search this summer for a successor to its president, Jonathan F. Fanton, who will depart in September 2009 under the foundation’s term-limits policy.

Mr. Fanton, who has headed MacArthur since Sept. 1, 1999, announced the plan in a letter to grant recipients and local leaders. MacArthur limits its president to two five-year terms.

“I have been privileged to lead MacArthur for a decade in which our philanthropy has grown from $170-million to nearly $300-million annually and become more sharply focused,” Mr. Fanton wrote. “I am particularly proud of our leadership in the fields of international justice, affordable housing preservation, and community development.”

Mr. Fanton — who before joining MacArthur served as president of the New School for Social Research, in New York, for 17 years — is MacArthur’s third president. He succeeded Adele Simmons, who served from 1989 to 1999, and John Corbally, who served from 1979 to 1989.

Mr. Fanton, who was hired with the understanding his tenure would be limited to 10 years, said in an interview that he is a strong proponent of term limits.

In addition to the rules that apply to the president, MacArthur limits board members to three four-year terms, program directors to two five-year terms, and program officers to three three-year terms, said Andrew Solomon, a spokesman.

Organizations that hold a “privileged position in society” benefit by regularly refreshing their staff, Mr. Fanton said. “It’s also good for people planning their careers to know what their options are, to understand that this privileged environment isn’t forever, that one has to return to the real world, so to speak, at some point.”

MacArthur — best known to the general public for its annual MacArthur Fellowships, or “genius” awards — is the country’s seventh-largest foundation, with assets in 2007 of almost $7-billion, according to a recent Chronicle of Philanthropy survey.

In his letter, Mr. Fanton also highlighted a $50-million MacArthur program that is financing research on how digital technologies are affecting the way young people learn and engage in civic life. Mr. Fanton has himself taken up cutting-edge digital technologies, attracting news coverage for leading several discussions in Second Life, the online world, as an “avatar,” or virtual character, named Jonathan MacFound.

Mr. Fanton said that in his final year, MacArthur will announce a new project on Asian regional security and step up a program to strengthen African regional human-rights bodies. It will also start three new domestic research projects — on fiscal challenges facing the United States, the consequences of longer life expectancies, and long-term measurement of the costs and benefits of social programs.

Mr. Fanton, who is 65, said he is not ready to retire and imagines he will explore options in philanthropy, academe, or government. “I enjoy being active and building institutions,” he said.