Obama: 'By Aug. 31, 2010, Combat Mission in Iraq Will End'

President Obama made it official today, announcing that he will end U.S. combat operations for the majority U.S. troops in Iraq by Aug. 31, 2010.

Within 18 months, officials expect that 90,000 of the current 142,000 U.S. troops in Iraq will have withdrawn, leaving between 35,000 and 50,000 troops to train, equip and advise Iraqi Security Forces, support the Iraqi government and conduct targeted counterterrorism missions.

Video of Barack Obama talking about raising military pay during a speech at Camp Lejeune.Play

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"The United States will pursue a new strategy to end the war in Iraq through a transition to full Iraqi responsibility," Obama said.

"America's men and women in uniform have fought block by block, province by province, year after year, to give the Iraqis this chance to choose a better future. Now, we must ask the Iraqi people to seize it," he said.

"Let me say this as plainly as I can: By Aug. 31, 2010, our combat mission in Iraq will end," Obama said, triggering applause from the Marines.

The president called Iraqi Prime Minister Nuri Al-Maliki and former President George W. Bush from Air Force One en route to the speech to brief them on what he would say.

The plan has drawn guarded support from Sen. John McCain, R-Ariz., who battled Obama over his Iraq withdrawal plans throughout the long presidential campaign.

"I am cautiously optimistic that the plans, as laid out by the president, can lead to success," McCain said.

But the plan has disappointed leading Democrats, including Senate Majority Leader Harry Reid, D-Nev., and House Speaker Nancy Pelosi, D-Calif., who are surprised that Obama plans to leave such a large contingent of Americans in Iraq.

"I think that's a mistake," said Rep. Lynn Woosley, D-Calif. "He promised the country he would have everybody out by 16 months after he was sworn in."

Addressing an audience of Marines at Camp Lejeune, N.C., Obama said America's six-year Iraq experience "has already been a long war," and he praised the country's military.

"You have fought against tyranny and disorder. You have bled for your best friends and for unknown Iraqis. And you have borne an enormous burden for your fellow citizens," he said.

Obama won more applause when he praised the nation's soldiers, telling them, "In an age when so many people and institutions have acted irresponsibly, you did the opposite – you volunteered to bear the heaviest burden."

But he got a roar of approval when he promised to reward the nation's fighters by raising their pay.

"I figured that would be an applause line," he said with a grin.

Obama warned Americans, "Let there be no doubt: Iraq is not yet secure, and there will be difficult days ahead. Violence will continue to be a part of life in Iraq.

The president also wanted to "take a moment to speak directly to the people of Iraq."

"We Americans have offered our most precious resource -- our young men and women -- to work with you to rebuild what was destroyed by despotism," he said, adding, "We seek a full transition to Iraqi responsibility for the security of your country."

Withdrawal from a stable Iraq, Obama said, would usher in "a new era of American leadership and engagement in the Middle East."

"The United States will pursue principled and sustained engagement with all of the nations in the region, and that will include Iran and Syria," he said. The U.S. does not have diplomatic relations with Iran and accuses both countries of backing terrorist groups like Hezbollah.

Former Massachusetts Gov. Mitt Romney, a Republican candidate who took issue on the campaign trail with Obama's Iraq pullout plans, remained firmly in opposition.

"It is in spite of Barack Obama's stance on Iraq, not because of it, that the troops are coming home in victory," he said at a speech to the Conservative Political Action Conference Friday evening.

McCain noted that it will be important for Obama to remain open to changing the plan as the situation on the ground warrants.

"I think it's important to point out that the president's plan is not without risk," he said. "We have not yet completed the mission in Iraq, and the gains we have made there remain fragile. We'll need to be cautious as we withdraw troops so as not to jeopardize these achievements and listen closely to the commanders on the ground as the administration determines the pace of withdrawals."

McCain this morning warned that Americans should not think that the troops who will remain in Iraq under the Obama plan would not be in danger.

"The American people should be clear, the president's plan, even after the end of its withdrawal timeline is reached, will leave in place up to 50,000 U.S. troops. All will be in harm's way. Some will continue to conduct combat operations," he said.

McCain said the president should not "succumb to pressures to make deeper or faster cuts in force levels."

Those pressures will come primarily from Obama's own party.

Reid said on Thursday, "I have been one for a long time that's called for significant cutbacks in Iraq, and I am happy to listen to the secretary of defense and the president, but when they talk about 50,000, that's a little higher number than I had anticipated."

After the speech today, Reid called it a "sound and measured plan," but suggested some disagreement by adding that the administration "must keep in Iraq only those forces necessary for the security of our remaining troops and the Iraqi people."

Sen. Carl Levin, D-Mich., chairman of the Senate Armed Services Committee, said that the president's plan was "reasonable," but underwhelming.

"I had expected that the size of the residual force would have been lower than 35,000 to 50,000 troops, given the limited missions remaining after the brigade combat teams are removed," he said.

Officials told ABC News said the plan "will responsibly redeploy our troops" and in doing so, Obama "is living up to a commitment he made."

The officials said that under the plan, the remaining U.S. forces would be reconstituted into "Advisory and Assistance Brigades. According to the officials, these brigades will not be combat units, but units with different force structures that have been specifically retrained to conduct training and advising mission.

A large portion of the remaining American forces will be combat support troops and only a very small percentage of the remaining troops will undertake the counterterrorism mission. U.S. forces will still be able to defend themselves, but after Aug. 31, 2010, American troops will not be responsible for providing security to large areas of Iraq as they do now.

On Thursday, Defense Secretary Robert Gates said that the size of the residual force should be considered "a way station" since the current Status of Forces Agreement with Iraq calls for all American troops to be out of that country by the end of 2011.

Gates and Joint Chiefs Chair Admiral Mike Mullen told ABC News that President Bush's troop surge helped make Obama's announcement a reality.

"It clearly has put us in a very different place in terms of where Iraq is," Gates said.

Many specifics of the plan remain to be determined by the top U.S. commander in Iraq, Gen. Ray Odierno, but both officials said that troop reductions will begin later this spring and continue through the summer.

"Exact force levels will be risk-dependent, and the pacing will be in the hands of commanders with the goal and direction of the president to end the combat role by Aug. 31, [2010]," said one official.

The 18-month plan was a compromise between Obama's campaign promise to pull combat troops out of Iraq in 16 months and concerns raised by military commanders about the need for additional forces to maintain the security gains of the past year.

One official said military commanders made a compelling argument to the president that "they wanted increased flexibility" around upcoming key events this year, such as regional elections over the summer and a national election in December.

There had been a "meeting of the minds" between senior military commanders and the president since Jan. 21 when he asked Gates and Adm. Mike Mullen, chairman of the Joint Chiefs of Staff, to explore plans to reduce the number of combat troops in Iraq, an official told ABC News.

On Thursday, White House spokesman Robert Gibbs said the president had asked his national security team "to put together a plan that they and he believed would accomplish the goal of removing our combat forces from Iraq in the most responsible way."

At the White House on Thursday night, the president briefed congressional leaders on the plan. Rep. John McHugh, R-N.Y., the top Republican on the House Armed Services Committee released a statement after the meeting that during the meeting the president provided reassurances that he would "revisit" his withdrawal plan if the violence were to worsen.

"President Obama assured me that there is a 'Plan B'," said McHugh.