WASHINGTON — Three years ago today, as they ordered more than 150,000 U.S. troops to race toward Baghdad, Iraq, Bush administration officials confidently predicted that Iraq quickly would evolve into a prosperous, oil-fueled democracy. When those goals proved optimistic, they lowered their sights, focusing on a military campaign to defeat Sunni-led insurgents and elections to jump-start a new political order.

Now, as the conflict enters its fourth year, the Bush administration faces a new challenge: the prospect of civil war. And, in response, officials appear to be redefining success downward again. If Iraq can avoid all-out civil war, they say, if Baghdad's new security forces can hold together, if Sunnis, Shiites and Kurds all participate in a new unity government, that may be enough to allow the administration to begin reducing the number of U.S. troops in the country by the second half of this year.

In increasingly sober public statements — and in slightly more candid assessments in interviews with officials who refused to be identified — administration officials are working to lower expectations.

"It may seem difficult at times to understand how we can say that progress is being made," President Bush said in his weekly radio address Saturday, acknowledging that much of the recent news from Iraq has been bad. "But . . . slowly but surely, our strategy is getting results."

"We may fail," warned a senior official directly involved in Iraq policy. "But I think we're going to succeed. I think we're going to nudge this ball down the road. . . . It's not going to be easy, and it's going to take time."

Pandora's box?

The administration's more sober tone is not entirely new; officials from Bush on down tacitly have acknowledged for more than a year that stabilizing Iraq has been more difficult than they expected when they launched the war in 2003.

But independent foreign-policy analysts say they see signs of a more fundamental shift in the administration's position — a creeping redefinition of U.S. goals in Iraq that increasingly allows for the possibility that Iraq may remain unstable and unhappy for years to come.

"It isn't going to be perfect," U.S. Defense Secretary Donald H. Rumsfeld said last month. "It isn't going to be pretty. It isn't going to look like the United States of America. It's going to be an Iraqi solution politically, an Iraqi solution economically and an Iraqi solution from a security standpoint."