(Adds Levin, McCain, Warner, Graham)

Sept 11 (Reuters) - The top U.S. commander in Iraq, Army Gen. David Petraeus, and U.S. Ambassador to Iraq Ryan Crocker defended U.S. war strategy on Tuesday in the face of criticism from members of the Senate Foreign Relations Committee.

Following are some quotes from senators at the hearing:

FOREIGN RELATIONS COMMITTEE CHAIRMAN JOSEPH BIDEN, A DELAWARE DEMOCRAT AND 2008 PRESIDENTIAL CANDIDATE: "The American people will not support an infinite war whose sole remaining purpose is to prevent the situation in Iraq from becoming worse than it is today."

FOREIGN AFFAIRS COMMITTEE RANKING REPUBLICAN RICHARD LUGAR OF INDIANA: "Military planning and diplomacy related to any 'Plan B' are constrained by concerns that either would be perceived as evidence of a lack of confidence in the president's surge strategy. We need to lay the groundwork for sustainable alternatives."

ARMED SERVICES COMMITTEE CHAIRMAN CARL LEVIN, A MICHIGAN DEMOCRAT: "Telling the Iraqis the surge will end by the middle of next year ... does not change our course. It presents an illusion of change to prevent a real change of course from occurring -- it is aimed at taking the steam out of the engine of change."

ARMED SERVICES COMMITTEE RANKING REPUBLICAN JOHN MCCAIN OF ARIZONA, A 2008 PRESIDENTIAL CANDIDATE: "General Petraeus and his troops ask just two things of us: the time to continue this strategy and the support they need to carry out their mission. They must have both, and we should fight to ensure that they do."

ILLINOIS DEMOCRATIC SEN. BARACK OBAMA, A 2008 PRESIDENTIAL CANDIDATE: "We have now set the bar so low that modest improvement in what was a completely chaotic situation ... is considered success. And it's not. This continues to be a disastrous foreign policy mistake."

VIRGINIA REPUBLICAN SEN. JOHN WARNER: "I hope in the recesses of your heart that you know that strategy will continue the casualties, the stress on our forces, the stress on military families, the stress on all Americans."

CONNECTICUT DEMOCRATIC SEN. CHRIS DODD, A 2008 PRESIDENTIAL CANDIDATE: "I don't get a feeling here that there's any real opportunity or optimism, that this is going to get better."

NEBRASKA REPUBLICAN SEN. CHUCK HAGEL: "Are we going to continue to invest American blood and treasure at the same rate we are doing now, for what? The president said, 'Let's buy time.' Buy time? For what?"

SOUTH CAROLINA REPUBLICAN SEN. LINDSEY GRAHAM: "This (Iraqi) government is in a dysfunctional state. The point I'm trying to make (is) there's a difference between still trying and not trying."

CALIFORNIA DEMOCRATIC SEN. BARBARA BOXER: "We are sending our troops where they're not wanted, with no end in sight, in the middle of a civil war, in the middle of the mother of all mistakes."

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