US national security adviser Ms Condoleezza Rice is expected to be nominated later today as replacement for US Secretary of State Colin Powell, who resigned yesterday.
Mr Powell, viewed as a moderate in the right-wing Republican administration, is the top official to quit since President George W. Bush's re-election, and was one of four Cabinet resignations announced by the White House yesterday.
Ms Rice, one of Mr Bush's closest confidantes who has generally sided with hard-liners in the administration, will be nominated to replace him, senior administration officials said. The nomination would have to be ratified by the Senate.
Mr Bush also planned to name Ms Rice's deputy, Mr Stephen Hadley, to take her job, they said.
Ms Rice, national security adviser since Mr Bush took office in January 2001, has spent more time with the president than any other of his top aides except White House Chief of Staff Andrew Card.
The change at the head of US diplomacy comes as Washington makes a new push for Middle East peace following last week's death of Palestinian President Yasser Arafat.
Mr Powell, who is expected to stay on the job until mid-January, will visit the region this month to possibly meet Palestinian leaders. Ms Rice met Palestinian Prime Minister Ahmed Korei in Berlin in May in what was the highest-level US contact with Mr Korei at the time.