Chicago - The call by Prime Minister Nuri Kamal al-Maliki for a timetable for the removal of American troops from Iraq presents an enormous opportunity. We should seize this moment to begin the phased redeployment of combat troops that I have long advocated, and that is needed for long-term success in Iraq and the security interests of the United States.

    The differences on Iraq in this campaign are deep. Unlike Senator John McCain, I opposed the war in Iraq before it began, and would end it as president. I believed it was a grave mistake to allow ourselves to be distracted from the fight against Al Qaeda and the Taliban by invading a country that posed no imminent threat and had nothing to do with the 9/11 attacks. Since then, more than 4,000 Americans have died and we have spent nearly $1 trillion. Our military is overstretched. Nearly every threat we face - from Afghanistan to Al Qaeda to Iran - has grown.

    In the 18 months since President Bush announced the surge, our troops have performed heroically in bringing down the level of violence. New tactics have protected the Iraqi population, and the Sunni tribes have rejected Al Qaeda - greatly weakening its effectiveness.

    But the same factors that led me to oppose the surge still hold true. The strain on our military has grown, the situation in Afghanistan has deteriorated and we've spent nearly $200 billion more in Iraq than we had budgeted. Iraq's leaders have failed to invest tens of billions of dollars in oil revenues in rebuilding their own country, and they have not reached the political accommodation that was the stated purpose of the surge.

    The good news is that Iraq's leaders want to take responsibility for their country by negotiating a timetable for the removal of American troops. Meanwhile, Lt. Gen. James Dubik, the American officer in charge of training Iraq's security forces, estimates that the Iraqi Army and police will be ready to assume responsibility for security in 2009.

    Only by redeploying our troops can we press the Iraqis to reach comprehensive political accommodation and achieve a successful transition to Iraqis' taking responsibility for the security and stability of their country. Instead of seizing the moment and encouraging Iraqis to step up, the Bush administration and Senator McCain are refusing to embrace this transition - despite their previous commitments to respect the will of Iraq's sovereign government. They call any timetable for the removal of American troops "surrender," even though we would be turning Iraq over to a sovereign Iraqi government.

    But this is not a strategy for success - it is a strategy for staying that runs contrary to the will of the Iraqi people, the American people and the security interests of the United States. That is why, on my first day in office, I would give the military a new mission: ending this war.

    As I've said many times, we must be as careful getting out of Iraq as we were careless getting in. We can safely redeploy our combat brigades at a pace that would remove them in 16 months. That would be the summer of 2010 - two years from now, and more than seven years after the war began. After this redeployment, a residual force in Iraq would perform limited missions: going after any remnants of Al Qaeda in Mesopotamia, protecting American service members and, so long as the Iraqis make political progress, training Iraqi security forces. That would not be a precipitous withdrawal.

    In carrying out this strategy, we would inevitably need to make tactical adjustments. As I have often said, I would consult with commanders on the ground and the Iraqi government to ensure that our troops were redeployed safely, and our interests protected. We would move them from secure areas first and volatile areas later. We would pursue a diplomatic offensive with every nation in the region on behalf of Iraq's stability, and commit $2 billion to a new international effort to support Iraq's refugees.

    Ending the war is essential to meeting our broader strategic goals, starting in Afghanistan and Pakistan, where the Taliban is resurgent and Al Qaeda has a safe haven. Iraq is not the central front in the war on terrorism, and it never has been. As Adm. Mike Mullen, the chairman of the Joint Chiefs of Staff, recently pointed out, we won't have sufficient resources to finish the job in Afghanistan until we reduce our commitment to Iraq.

    As president, I would pursue a new strategy, and begin by providing at least two additional combat brigades to support our effort in Afghanistan. We need more troops, more helicopters, better intelligence-gathering and more nonmilitary assistance to accomplish the mission there. I would not hold our military, our resources and our foreign policy hostage to a misguided desire to maintain permanent bases in Iraq.

    In this campaign, there are honest differences over Iraq, and we should discuss them with the thoroughness they deserve. Unlike Senator McCain, I would make it absolutely clear that we seek no presence in Iraq similar to our permanent bases in South Korea, and would redeploy our troops out of Iraq and focus on the broader security challenges that we face. But for far too long, those responsible for the greatest strategic blunder in the recent history of American foreign policy have ignored useful debate in favor of making false charges about flip-flops and surrender.

    It's not going to work this time. It's time to end this war.

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    Barack Obama, a United States senator from Illinois, is the presumptive Democratic presidential nominee.