In a stunning turn for a team less than one year removed from a World Series championship, the Giants announced Wednesday night that managing general partner Bill Neukom will retire at the end of the year, a decision that sources said came at the request of the ownership group's powerful executive committee. Neukom will be replaced on Dec. 31 by team President and Chief Operating Officer Larry Baer, who will become chief executive officer. Neukom will be named chairman emeritus, the team said. He is expected to sell his stake in the team to other investors.