ABOARD AIR FORCE ONE, Sept 3 (Reuters) - U.S. President George W. Bush has left Iraq after a surprise visit on Monday to a heavily guarded desert air base, the White House said. Bush stopped in Iraq on his way to Sydney, Australia, where he was scheduled to arrive on Tuesday to attend a summit of Asia-Pacific leaders. (World Desk Americas, editing by Peter Cooney; 1-202-7898-8457))