WASHINGTON (CNN) -- Sen. Susan Collins, R-Maine, told CNN Tuesday she will consider calling for troops to be withdrawn from Iraq if sufficient progress has not been made in the country by September -- the next time the top U.S. commander in Iraq, Gen. David Petraeus, returns to Capitol Hill to update Congress.

This is the first time Collins, a moderate who is bracing for a tough re-election fight next year, has suggested she might call for a troop withdrawal in the coming months.

"I do believe there comes a point in September where if it's evident that the new strategy is not successful and will not succeed we do have to change course and that means looking for all options, including a plan for withdrawing troops," Collins said.

Collins has been critical of the war in the past, but has resisted timetables for withdrawal. She is a top Democratic target in 2008 and two anti-war groups have already started running ads against her.

Any withdrawal would be "gradual but significant," she added Tuesday.