President Bush on June 25 nominated James A. Williams, a senior General Services Administration official, to be the agency’s new chief. Williams has led GSA’s Federal Acquisition Service since 2006. GSA Acting Administrator David Bibb will retire on Sept. 1 to pursue a real estate industry position. Bibb, a longtime GSA official, became its acting head after Lurita Doan resigned on April 30. David Winstead remains GSA’s public buildings service commissioner.