For planning purposes, the Army is gearing up to keep current troop levels in Iraq for another four years, a new indication that conditions there are too unstable to foresee an end to the war. Gen. Peter Schoomaker, the Army chief of staff, cautioned against reading too much into the planning, which is done far in advance to prepare the right mix of combat units for expected deployments. He noted that it is easier to scale back later if conditions allow, than to ramp up if they don't, the Associated Press reported. "This is not a prediction that things are going poorly or better," Schoomaker told reporters. "It's just that I have to have enough ammo in the magazine that I can continue to shoot as long as they want us to shoot." Even so, his comments were the latest acknowledgment by Pentagon officials that a significant withdrawal of troops from Iraq is not likely in the immediate future. There are now 141,000 U.S. troops there. At a Pentagon news conference, the top U.S. commander in Iraq, Gen. George Casey, said that as recently as July he had expected to be able to recommend a substantial reduction in U.S. forces by now. But that plan was dropped as sectarian violence in Baghdad escalated. While arguing that progress is still being made toward unifying Iraq's fractured political rivalries and stabilizing the country, Casey also said the violence amounts to "a difficult situation that's likely to remain that way for some time." He made no predictions of future U.S. troop reductions. Appearing with Casey, Defense Secretary Donald H. Rumsfeld said he and other senior Pentagon officials are still studying how the military might keep up the current pace of Iraq deployments without overtaxing the Army and Marine Corps, which have borne the brunt of the conflict. Rumsfeld said one option is to make more use of the Air Force and Navy for work that normally is done by soldiers and Marines.