President-elect Barack Obama has asked Defense Secretary Robert Gates to remain in office for the beginning of Obama's presidential term. An official familiar with the discussions said Tuesday that Gates will remain in the post for at least a year. The official spoke on the condition of anonymity because Obama is not ready to announce his decision. Obama is expected to announce the selection of Gates and other members of a national security brain trust next week. Gates has served as President George W. Bush's defense chief for two years. Gates is a moderate Republican with long-standing ties to the Bush family. His appointment would fulfill an Obama pledge to include a Republican in his Cabinet.