WASHINGTON -- Two members of a Washington think-tank who have been critical of the handling of the Iraq war in the past have expressed some cautious optimism.

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Michael O'Hanlon and Kenneth Pollack of the Brookings Institution spent a little more than a week in Iraq. In an op-ed piece in The New York Times, they said they were surprised by the "gains" they saw, and the chances for a "sustainable stability" that the U.S. and the Iraqis could "live with."

The U.S. "is finally getting somewhere," the pair said, adding that extremist elements are being weeded out, and that U.S. troops now feel they have enough resources to make a difference.

Iraqi military units seem well-integrated in terms of religion and ethnicity, the pair said. The trouble, however, lies in Baghdad, especially in the most ethnically charged neighborhoods, where they said peacekeeping troops may need to stay "for several years."

Politicians in Baghdad are "a big problem," they said. Without more political progress, the Brookings fellows said the U.S. will need to decide just when to go ahead and "pull the plug."

'Not Hopeless'

Army Gen. David H. Petraeus, the senior commander in Iraq, said Tuesday that the American people understand that the United States cannot completely "unhook" from Iraq.

"The question is, 'What is the nature of our support, and what is the level of that support?'" Petraeus said on "Good Morning America."

"I'm a realist," Petraeus said. The bombing of the Golden Mosque in Samarra in February 2006 ignited sectarian violence, which reached damaging levels in the winter. Petraeus said the level of violence was such "that the very fabric of Iraqi society has been torn."

The way forward in Iraq will be hard but "not hopeless," he said.

"There is an awful lot of soul-searching that goes on when you are the commander of an endeavor like this, and you do occasionally ask yourself if this is worth it," he said.

"I think it is, or I wouldn't be engaged in it. But I ask myself periodically. I think any commander should do that, must do it."

Systems Need Help

Marine Corps Maj. Gen. W.E. Gaskin said the country's outdated network for maintaining and repairing critical war-fighting gear is a major hurdle in the U.S. effort to fashion an independent Iraqi fighting force.

He said the troops themselves will be ready for sustained operations in about a year. But Gaskin added that he's "not as optimistic about them being able to fix the logistics system."

While the U.S. system is largely automated, Iraq's is all paperwork. And Iraq relies largely on private Iraqi contractors for repairs, he said.

Gaskin also said many of the Iraqis who could make the flawed process function were lost when the country's army was disbanded in May 2003.

Slow Progress Undermines Credibility

President George W. Bush's nominee to head the Joint Chiefs of Staff said Monday that slow progress in Iraq is undermining U.S. credibility and emboldening Iran's regional ambitions.

In written answers to prepared questions from the Senate Armed Services Committee, Adm. Michael Mullen said those concerns can be eased by successes on the ground in Iraq. According to Mullen, there's been steady progress on that front.

But Mullen said there's been only limited headway in achieving reconciliation among Iraq's political factions. And he said resolving that conflict remains the precondition for an Iraq that can govern, defend and sustain itself and be an ally in the war on terror.

Mullen is currently chief of naval operations and was selected to replace Marine Corps Gen. Peter Pace.

The committee is scheduled to consider Mullen's nomination on Wednesday.