WASHINGTON — The top American commander in the Middle East told a Senate panel yesterday that escalating sectarian violence in Iraq could propel the country toward a civil war.

The commander of the American Central Command, Army General John Abizaid, also said American forces could take more casualties as they carry out a new plan to reinforce Baghdad, and he cast doubt on earlier predictions that the American troop level in Iraq could be drawn down this year.

General Abizaid, appearing before the Senate Armed Services Committee with Defense Secretary Rumsfeld and the chairman of the Joint Chiefs of Staff, General Peter Pace, made the comments after the British ambassador to Iraq reported in a diplomatic dispatch that Iraq was more likely headed to “low intensity civil war” and sectarian partition than to a stable democracy.

The British Broadcasting Corporation reported that the assessment was contained in the final diplomatic cable from William Patey to Prime Minister Blair and top members of Mr. Blair’s Cabinet before Mr. Patey left the Iraqi capital last week.

In his comments yesterday, General Abizaid did not dispute Mr. Patey’s assessment.

Asked by Senator Levin, a Democrat of Michigan, whether he agreed that “Iraq is sliding toward civil war,” General Abizaid replied, “I believe that the sectarian violence is probably as bad as I’ve seen it, in Baghdad in particular, and that if not stopped, it is possible that Iraq could move towards civil war.”

In response to a question from the committee chairman, Senator Warner, a Republican of Virginia, on the American military mission in Iraq in the event of civil war, General Pace said, “I believe that we do have the possibility of that devolving to a civil war, but that does not have to be a fact.”

General Pace said the American armed forces can continue to help provide security to allow the Iraqi government to govern and provide economic opportunity to its citizens but that “the weight of that opportunity rests with the Iraqi people.”

General Pace added, “We can provide support. We can help provide security, but they must now decide about their sectarian violence.” He said Iraq’s rival Shiite and Sunni Muslims “are going to have to love their children more than they hate each other. If they do that and seize the opportunity that the international community has provided to them, then this will be what we want it to be, which is a success for ourselves and the Iraqi people. But the weight of that shift must be on the Iraqi people and Iraqi government.”

In his opening remarks to the committee, General Abizaid said, “A couple of days ago, I returned from the Middle East. I’ve rarely seen it so unsettled or so volatile. There’s an obvious struggle in the region between moderates and extremists that touches every aspect of life.”

Asked whether he shares the recently expressed view of the top American commander in Iraq, General George Casey Jr., that troop levels could be reduced this year, General Abizaid said that since General Casey made that statement in June, it has become “clear that the operational and the tactical situation in Baghdad is such that it requires additional security forces, both U.S. and Iraqi.”

General Abizaid told the committee, “I think the most important thing ahead of us throughout the remainder of this year is ensuring that the Baghdad security situation be brought under control. It’s possible to imagine some reductions in forces, but I think the most important thing to imagine is Baghdad coming under the control of the Iraqi government.”

General Abizaid came under some tough questioning from Senator McCain, a Republican of Arizona, about the American plan to move troops into Baghdad from elsewhere in Iraq, a move the senator suggested would leave other potential hot spots more vulnerable. Mr. McCain pressed the general on whether the insurgent stronghold of Ramadi in western Iraq is “under control,” and General Abizaid declined to affirm that it was, saying instead that “the situation in Ramadi is better than it was two months ago.” He said about 3,500 troops from Mosul, plus military police, would be moving to Baghdad to help reduce the violence there.

Mr. McCain said, “What I worry about is we’re playing a game of whack-a-mole here,” with insurgent activity popping up in places that troops have vacated. “Now we’re going to have to move troops into Baghdad from someplace else. It’s very disturbing.”

Asked if putting more American troops into the “very volatile situation” in Baghdad likely means increased casualties, General Abizaid said, “I think it’s possible that in the period ahead of us in Baghdad, that we’ll take increased casualties. It’s possible.”

Senator Clinton, a Democrat of New York, confronted Mr. Rumsfeld in prepared opening remarks, telling him he did not send enough troops to Iraq in the 2003 invasion “to establish law and order,” erred by disbanding the Iraqi army, failed to plan adequately for the occupation phase, and “underestimated the nature and strength of the insurgency, the sectarian violence, and the spread of Iranian influence.”

Mrs. Clinton told Mr. Rumsfeld, “We hear a lot of happy talk and rosy scenarios, but because of the administration’s strategic blunders and, frankly, the record of incompetence in executing, you are presiding over a failed policy.”

“My goodness,” Mr. Rumsfeld answered, rejecting the criticism. Regarding the initial number of troops sent into Iraq, which has also been a sore point with Mr. McCain, the defense secretary said, “I guess history will make a judgment on that.”

The assessment by the departed British ambassador to Iraq, Mr. Patey, was regarded as significant in part because the British government maintains troops in Iraq and has supported the Bush administration’s Iraq policy. Other commentators share Mr. Patey’s views, but few, if any, officials allied with the American-led coalition have said so publicly.