April 8 (Reuters) - U.S. presidential candidates John McCain and Hillary Clinton pushed competing positions on Iraq during hearings on Tuesday with Gen. David Petraeus, the top U.S. commander in Iraq.

Barack Obama, the front-runner for the Democratic presidential nomination, was scheduled to face Petraeus at another hearing later in the day.

Here is a sampling of quotes from the candidates:

ARIZONA SEN. JOHN MCCAIN, REPUBLICAN

"We're no longer staring into the abyss of defeat and we can now look ahead to the genuine prospect of success."

"American failure would almost certainly require us to return to Iraq or draw us into a wider and far far costlier war."

If U.S. troops withdraw before stability is established, "we will exchange for this victory a defeat that is terrible and long-lasting. Al Qaeda in Iraq would proclaim victory, increase its efforts to provoke sectarian tensions, pushing for a full-scale civil war that could descend into genocide and destabilize the Middle East."

NEW YORK SEN. HILLARY CLINTON, DEMOCRAT

"I think it's time to begin an orderly process of withdrawing our troops, start rebuilding our military and focusing on the challenges posed by Afghanistan, the global terrorist groups and other problems that confront Americans," she told the hearing.

"The (Bush) administration and supporters of the administration policy often talk about the cost of leaving Iraq, yet ignore the greater costs of continuing the same failed policy." (Reporting by Andy Sullivan and Jeff Mason, editing by Todd Eastham)

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