US President George W. Bush is installing two experienced commanders from vastly different backgrounds to carry out the new Iraq policy he will announce next week, substituting them for generals who had qualms about a fresh buildup of US troops in the war zone. One of the new military chiefs, Lt. Gen. David Petraeus, is an Iraq veteran who wrote a dissertation at Princeton University titled "The American Military and the Lessons of Vietnam." Iraq has drawn more and more comparisons to that quagmire. The other new man, Adm. William Fallon, is a Navy veteran who to some is an odd choice to oversee a ground conflict in a nearly landlocked country. Yet as top US commander in the Pacific, he has experience in a region that, like the Middle East, has several trouble spots. Some former military officers said whether the two succeed depends less on their resumes than on Bush's new policy, which he will announce as early as Wednesday. Adding thousands of additional US troops to the 132,000 already there is a leading proposal he is considering, along with new economic and political approaches.