General David Petraeus, the top US commander in Iraq who hinted months ago that he wanted to halt troop reductions after the “surge” was unwound this summer, will be under pressure on Tuesday to provide details about the “pause” when he appears before lawmakers in Congress.

The length of the pause will determine how many US troops remain in Iraq when the next president takes office. Many experts expect to see more US soldiers in Iraq in January 2009 than two years earlier, when President George W. Bush ordered a surge of 30,000 additional forces.