Bush told reporters at the White House that the plan is "broadly acceptable to the Iraqi people."
He spoke after meeting with British Prime Minister Tony Blair, who also voiced support for the plan. Bush and Blair also vowed to stick to the June 30 timetable for turning over power to Iraqis.
UN envoy Lakhdar Brahimi is due back in New York soon to report to the UN secretary-general -- before returning to Iraq for more talks with Iraqis.
He's proposed a caretaker government that would be led by a prime minister, with a president as head of state, and two vice presidents.
There would be a conference after June 30 to set up an assembly, with powers to consult, but not to legislate.