New York ? The head of the agency overseeing development of the World Trade Center site announced Thursday he is stepping down at the end of the month.

John C. Whitehead, chairman of the Lower Manhattan Development Corp., also is leaving his post as chairman of the World Trade Center Memorial Foundation, which is raising money to build the memorial. He will remain on its board.

Thomas Johnson, the retired CEO of GreenPoint Financial Corp. who lost his son in the Sept. 11, 2001, attack, took over his duties at the foundation; the board will elect a new chairman.