Those comments from Gen David H Petraeus were met by sharp criticism from a senior Democrat, Senator Carl Levin of Michigan, that the Bush administration had adopted “a war plan with no exit strategy.”

As hearings to define the future course of American strategy in Iraq opened on Tuesday morning, General Petraeus and Ambassador Ryan C Crocker, the American envoy to Baghdad, described an Iraq that is the scene of significant, if still-fragile, progress in security and politics. But they made that case without reference to Congressionally mandated benchmarks that defined their testimony last September.

General Petraeus said that security progress has been “significant but uneven.” Under questioning, he declined to estimate American troop levels beyond the withdrawal by July of five additional combat brigades sent to Iraq last year. And he acknowledged that the government’s recent offensive in Basra was not sufficiently well-planned.

The security situation remained in flux, General Petraeus said, in part because of the “destructive role Iran has played,” and he said that “special groups” of Shiite radicals supported from Tehran posed the greatest immediate threat to security. Ambassador Crocker added, “Iran has a choice to make.”

The General told senators that he was recommending a 45-day pause — which he defined as a period of “consolidation and evaluation” — before reviewing once again whether there should be further troop reductions.

“This process will be continuous, with recommendations for further reductions made as conditions permit,” General Petraeus said. “This approach does not allow establishment of a set withdrawal timetable. However, it does provide the flexibility those of us on the ground need to preserve the still-fragile security gains our troopers have fought so hard and sacrificed so much to achieve.”

The lethality of terrorists within Iraq who say they are aligned with al-Qaeda has been “reduced significantly,” General Petraeus said, but they continue to pose a worrisome threat. Only “relentless pressure” will guarantee that terrorists cannot regroup, he added.