President George W. Bush, opening a new push to defend his embattled war policy, said a US military pullout from Iraq would be a terrible mistake. His Pentagon chief said, "Quitting is not an exit strategy." Defense Secretary Donald H. Rumsfeld said of the Iraqis, "They know that they're the ones that are going to have to grab that country. And it's time." The administration is under pressure to convince increasingly skeptical Americans that the president's strategy for Iraq is headed in the right direction nearly three years after the US-led invasion. The president is to give a speech on the subject Wednesday at the Naval Academy, and the White House is to release a 35-page document titled "Our National Strategy for Victory in Iraq." The unrelenting violence that continues to claim American lives has contributed to a drop in Bush's popularity, to its lowest level yet, and to growing doubts about the war. It also has led to a debate in Congress about when the 160,000 US troops there should begin to come home.