America's top general said Saturday he would not rule out U.S. troop reductions in Iraq this year, even though troop levels were just increased in response to rising sectarian violence.

Marine Gen. Peter Pace, chairman of the Joint Chiefs of Staff, said in an interview aboard his plane on an overnight flight from Washington that the attitudes of rival Iraqi religious groups would be the ultimate decider of Iraq's fate as a nation — regardless of the size of the U.S. military force, which now numbers about 133,000.

Pace stopped short of predicting that conditions would improve enough to allow a U.S. troop reduction before year's end, but he said he would be consulting with top commanders this weekend on the outlook for a turnaround in the sectarian violence and the need for U.S. troops.

"It's important to always have troop levels on the table" as a subject for discussion, he said. "We thought as recently as a month or so ago that we were going to be able to come down" in the numbers. "What changed was the increase in sectarian violence," he added.

Nonetheless, Pace said it was possible that the sect-on-sect violence could be tamped down quickly. "Their leaders simply could decide to stop it" by telling their people to stop killing each other, he said.

"There is still the potential to reduce the number of troops," he said, although he would not say how soon he thought this could happen. Earlier this year U.S. officials were hoping to reduce troop levels to 100,000 or less by December, with more significant cuts following in 2007.

Pace was scheduled to meet with Gen. George Casey, the top U.S. commander in Iraq who won approval by Defense Secretary Donald H. Rumsfeld last month to extend the yearlong deployment of the 172nd Stryker Brigade for up to four months in order to add more U.S. firepower in Baghdad. That move dashed immediate hopes for an overall troop reduction and triggered talk among Democrats of the Bush administration breaking faith with the troops.

Pace said he intended to meet with commanders and soldiers of the Alaska-based 172nd to thank them for accepting the burden of an extended Iraq tour.

The Joint Chiefs chairman, on only his second trip to Iraq this year, also said that Pentagon officials are beginning to think about who might replace Casey, who has been the top commander in Iraq since July 2004. Pace said Casey would stay for about another six months.

"Certainly you start thinking now" about who should succeed Casey, Pace said. He offered no names but praised Casey's performance.

"He will not be easily replaced," Pace said.

Asked about the several recent cases of alleged criminal misconduct by U.S. troops, such as the Marines accused of killing 24 Iraqi civilians, including unarmed women and children, in the town of Haditha, Pace said he was troubled by even the possibility that the allegations will be proven in court.

"We should not accept anything other than zero" cases of criminal abuse, he said, dismissing suggestions that there inevitably are going to be cases of misbehavior in a large group such as the U.S. military.

"We should not allow ourselves to do math" to explain away misconduct, he said.

Pace also was meeting Saturday with Lt. Gen. Martin Dempsey, who is in charge of the U.S. effort to train the Iraqi security forces. Pace said the Iraqi forces now number about 277,000 and are on track to reach the final goal of 325,000 by the end of December.