The incoming Obama administration has notified all politically-appointed ambassadors that they must vacate their posts as of Jan. 20, the day President-elect Barack Obama takes the oath of office, a State Department official said. The clean slate will open up prime opportunities for the president-elect to reward political supporters with posts in London, Paris, Tokyo and the like. The notice to diplomatic posts was issued this week. Political ambassadors sometimes are permitted to stay on briefly during a new administration, but the sweeping nature of the directive suggests that Obama has little interest in retaining any of Bush's ambassadorial appointees.