The chairman of the Joint Chiefs of Staff is expected to advise President Bush to reduce the U.S. force in Iraq next year by almost half, potentially creating a rift with top White House officials and other military commanders over the course of the war. Administration and military officials say Marine Gen. Peter Pace is likely to convey concerns by the Joint Chiefs that keeping well in excess of 100,000 troops in Iraq through 2008 will severely strain the military. This assessment could collide with one being prepared by the U.S. commander in Iraq, Army Gen. David H. Petraeus, calling...