CalPERS will assemble a board subcommittee to begin searching to replace James E. Burton as CEO of the $151 billion fund. William Crist, board president, will appoint members to the subcommittee, said Brad Pacheco, spokesman the California Public Employees Retirement System, Sacramento. Names of appointees havent been announced, and Mr. Pacheco said he doesnt know if a recruiting firm will be used. After it is formed, the subcommittee will "begin the search immediately, Mr. Pacheco said, although Mr. Burton said he will stay until sometime in the fall. Mr. Burton plans to work in the private sector, but details about his plans were unavailable.