WASHINGTON, Sept 10 (Reuters) - U.S. Iraq commander Gen. David Petraeus began giving testimony before Congress on Monday in which he is expected to argue against a major reduction in the 168,000 U.S. forces in Iraq for now.

His appearance with U.S. Ambassador to Iraq Ryan Crocker will set the stage for Washington's political debate over how Republican President George W. Bush will conduct the war during his final 17 months in office.

Democrats won control of Congress last year on a promise to begin a phased troop withdrawal but do not have appear to have the votes to cut off funding for the war, in which more than 3,700 U.S. soldiers and tens of thousands of Iraqis have died.

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