After a cease-fire agreement with Muqtada al-Sadr, the Shi'ite cleric who leads one of the key dissident groups, Petraeus said the work to supplant the militias in the key southern port city continues. Petraeus and Crocker argued that the government has sent an important signal to its nation by taking on the militias in the south.

But in a blunt exchange with Petraeus, Sen. Jack Reed, D-R.I., argued that the rivalry between Sadr and Shi'ite government leaders is far from the point where it can be resolved by political means.

Petraeus said that some members of Sadr's militias will retire from the fight if the government can find them jobs.

Reed retorted that the clash between Maliki's allies in the government and Sadr's militias "is less an employment problem than it is an existential problem of the political survival of one or the other."

Reed used the example of Sadr's role in the conflict to argue that the internecine rivalries among Iraq's Shia groups remain intractable and fraught with the potential for violence.

But Petraeus argued that the multilateral cease-fire shows grounds for hope that the various rivals fear all-out warfare enough to consider political solutions.

"Everybody has again looked into the abyss" and pulled back from the fight, at least for the moment, Petraeus said.

Sen. Hillary Clinton of New York, a Democratic presidential candidate, a member of the committee said later that "might well be irresponsible to continue this policy that has not produced the results that have been promised time and time again at such a tremendous cost."

As a junior member of the Armed Services committee, Clinton waited her turn to question Petraeus almost three hours after the hearing began.

She asserted that beyond the obvious cost to the American military and treasury, the war in Iraq carries "opportunity costs" -- meaning, for example, lost opportunities in the counter-terrorism efforts in Afghanistan. She also stressed the view that the war has taken a great toll on the mental health of returning veterans.

Clinton said that while members of the Bush administration points to what it views as the potential cost of withdrawing forces from Iraq, "they ignore the greater cost of continuing the same failed policy."

U.S. Sen. Carl Levin, the Michigan Democrat who chairs the panel, said the only way to force the Iraqi government to take the political steps necessary for political reconciliation and stability is “to adopt a reasonable timetable for a change of mission and redeployment of most of our troops.”

"Promptly shifting responsibility to Iraqis for their own future -- politically, militarily, economically -- is the best hope for a successful outcome in Iraq and represents, finally, an exit strategy for most of our troops,” he said.

This morning, the hearing was briefly interrupted when a protester shouting, "Bring them home," had to be escorted from the room at about 10:43 a.m. Some audience members clapped.

Petraeus and Crocker are making their first of several appearances on Capitol Hill this week to update Congress on the status of the war in Iraq.

Petraeus told the committee that since his last testimony in September, “levels of violence and civilian deaths have been reduced substantially.” Al-Queada and other terrorist groups “have been dealt serious blows,” he said, and Iraqi government forces have significantly improved their position.

But in reference to a failed government defensive late last month against Shi'ite militia groups in the southern port city of Basra, Petraeus said the progress made since last spring is “fragile and reversible.”

A major point in testimony by Petraeus and Crocker is the potential need for a pause this summer in the long-scheduled reduction of troop strength in Iraq.