The most important immediate step, Bush and other officials said, is for Iraqi politicians from all three major groups to form a unity government. "I urge them . . . to form a government that can confront the terrorist threat and earn the trust and confidence of all Iraqis," Bush said Saturday.

That is proving difficult as well. Sunni and Kurdish leaders are unhappy with the decision by the largest Shiite bloc in the new parliament to re-elect Ibrahim al-Jaafari as prime minister. U.S. officials are unhappy with the choice, too; many of them privately consider al-Jaafari incompetent and divisive. The result, at least in the short run, has been a political deadlock.

"They have to step up to the plate," the senior official said, reflecting the administration's frustration with the Iraqis. "They cannot just sit aside and press their short-term interests."

Unless a unity government succeeds, warned a civilian adviser to the Pentagon, "You are heading for a de facto independent Kurdistan, a Shia Iraq that is very close to the Iranians, and a Sunni Iraq which is rebellious in perpetuity."

Civil war?

Until now, one of the major goals of U.S. policy in Iraq has been to avoid choosing sides in a divided Iraq. But that goal may be slipping away, outside analysts said.

"In a sense, as your own forces diminish, you have to choose sides," Dobbins said. "We may be forced to do that. We already have to some degree."

"The Sunnis already see us as having chosen sides," said Steven Biddle, a former professor at the U.S. Army War College who is now at the private Council on Foreign Relations.

Biddle has argued that by building new Iraqi security forces dominated by Shiites and Kurds, the United States effectively has armed and trained two of the three sides in Iraq's internal conflict. The Sunnis, he wrote in a recent article, "perceive the 'national' army and police force as a Shiite-Kurdish militia on steroids."

"I think we're in a civil war now. We've been in a civil war for more than a year. It's just a civil war that's being fought at low intensity," he said in an interview.

Instead of trying to build Iraqi security forces quickly, Biddle contends, the United States should slow down its training program, slow its own military withdrawal, and concentrate on strengthening political leaders — especially among the Sunnis — who can compromise.

But he acknowledges that there is no political support in the United States for a longer or larger U.S. troop deployment.

"If we had the troops, I'd increase the troops," he said. "But we don't have the troops."

A question of support

Administration officials acknowledge that waning U.S. public support for the war has become one of their major concerns, if only because Iraqis on all sides increasingly wonder how long the Americans will stay.