Barack Obama praised U.S. forces for the success of the surge in Iraq, but said success there is less important than the fact the U.S. should not have invaded in the first place.

Speaking to FOX News, the Democratic presidential candidate said attention has been focused on the surge because people tend to look at narrow tactics over broader questions. He acknowledged that the 30,000-troop surge that he opposed when it was announced in March 2007 "made absolutely a difference."

However, he added, that U.S. troops alone could not have brought peace to Iraq without Sunnis forming "Awakening Councils" that decided not to cooperate with Al Qaeda in Iraq and Shiite militias deciding to "stand down," all of which helped create a "significant reduction in violence.

"If you look at my judgment that we shouldn't have gone into Iraq, that Afghanistan posed a greater threat, that in fact we have been distracted from going after bin Laden and Al Qaeda, and that ultimately the stability of Iraq is going to depend on the ability of factions, the Shia, the Sunni, and the Kurds deciding they want to live together in some sort of peaceful accommodation, then I think I've been right," Obama said in an interview taped Friday in London and appearing Monday on FOX News.

"I think that the question -- the narrow question was, if you had Sunni and Shia fighting fiercely in a civil war, could U.S. troops alone solve that problem? And the fact is, is that as wonderful as our troops have performed, it took a whole series of elements to reduce the violence. That's a good thing," he said.

The Illinois senator, who traveled last week to Iraq and Afghanistan as part of a congressional delegation with Sens. Chuck Hagel, R-Neb., and Jack Reed, D-R.I., said he is "much more interested in the broader debate" of whether the U.S. should have entered Iraq in the first place, a position he opposed from the get-go. He said his strategy as president would be to figure out how to deal with more significant challenges while leaving some U.S. forces in the Mideast nation.

Obama spoke on the last day of a weeklong trip to Iraq, Afghanistan, Israel and Europe. Throughout his journey, Republican rival John McCain rapped him for refusing to recognize the success of the troop surge, and said Obama's opposition to the surge was calculated on political considerations.

"Senator Obama doesn't understand. He doesn't understand what's at stake here. And he chose to take a political path that would have helped him get the nomination of his party. ... And if we'd done what Senator Obama wanted done, it would have been chaos, genocide, increased Iranian influence, perhaps Al Qaeda establishing a base again," McCain said Sunday on ABC's "This Week."

Now 8 points up over McCain in the latest Gallup tracking poll, Obama continued to repeat that as commander in chief, his priority would be "to set the strategy, to set the policy, to set the mission," which would include a 16-month timetable for withdrawing troops from Iraq.

"My policy is that we made a mistake by going into Iraq. We're there now, which means we have to be as careful getting out as we were careless getting in," he said. That timetable would be tailored to a "pace that has been outlined not just by me, but by military commanders.

Obama's interview aired as Gen. David Petraeus, the head of Multinational Forces in Iraq, said he would provide an assessment in about a month about the possibility of further recommendations for troop reductions. Petraeus said that the recommendations will be based on conditions on the ground.

Besides Obama, officials in Washington have talked recently about the need for more troops in Afghanistan, and Petraeus said those statements do figure into his calculations about Iraq.

"The human cost and the financial cost and the strategic opportunity cost, if you will — the fact that forces are here, they can't be elsewhere — figures into the recommendations that I make," he told National Public Radio. "They are factors, so they do figure in, but they don't drive the recommendations."

Obama said even with a 16-month pullout, he would "leave residual forces to train Iraqi security forces, to make sure that we are providing security for our diplomats and civilians, and that we have a counterterror ... force in the region, they can do what it needs to do." He added that a withdrawal would enable the U.S. to send more brigades to Afghanistan.

That position is not fundamentally at odds with the McCain camp, the Bush administration or the Iraqi government, all of whom have said they would like to keep U.S. troops in the country. The U.S. and Iraq have been working for months on a Status of Forces Agreement that would detail the size and structure of that force.