Two thirds of Americans believe the United States is losing ground in Iraq, and less than half believe that US-led forces can leave a stable and democratic regime in Baghdad, according to a poll.

The Pew Research Center for the People and the Press found 66 percent of those surveyed believe the threat of a civil war in Iraq has increased.

That was sharply higher than the 48 percent who shared that opinion in January, before the destruction of the Shiite shrine in Samarra and the subsequent upsurge in violence.

"As the third anniversary of the start of the war in Iraq approaches, public support for keeping US troops in Iraq has reached its lowest point and assessments of progress there have turned significantly more negative than they were just a few months ago," the think tank said.

Only 49 percent of those polled believe that the United States will succeed in Iraq, down from around 55 percent for several months.

Trust in President George W. Bush's strategy for victory continues to sink: currently 70 percent believe he lacks a clear plan for successfully ending the war.

The poll, which has a five-point margin of error, was carried out among 1,405 people between March 8 and 12.