Obama plans to bring home next month the first batch of about 100,000 American servicemen currently in Afghanistan, with all combat troops leaving by 2014.
Huntsman, a former Utah governor who was Obama's ambassador to China, thinks that may not be fast enough because of the financial cost of the war and because of waning public support.
"When you look at Afghanistan, can we hang out until 2014 and beyond?" Huntsman asked. "You can, if you're willing to pay another quarter of a trillion dollars to do so."
In an interview aired Sunday on CNN's "State of the Union," he questioned whether the battle against the Taliban and other anti-government insurgents served U.S. national interests any longer.
He didn't mention last month's killing of al Qaeda leader Usama bin Laden, but his doubts appeared to be tapping into the growing sentiment in the United States that bin Laden's death should prompt a reassessment of the Afghan war effort.
One of the key goals on the military campaign was to ensure that Afghanistan never again could offer a haven to the group that killed nearly 3,000 Americans on Sept. 11, 2001.
"If it isn't in our direct national security interest and if there isn't a logical exit strategy and if we don't know what the cost is going to be in terms of money and human lives, then I think you have to say it's probably time we re-evaluate this," Huntsman said. He said continued U.S. engagement required that a "strong argument" be made to the American people.
But asked specifically if he would take American troops out sooner than 2014, Huntsman hedged.
"My hunch is the American people want to be out of there as quickly as we can get it done," he said. But, he added: "You're going to have to leave behind some presence, probably not 100,000 or 120,000 troops, but some presence."
If Huntsman's comments failed to outline a stark contrast in foreign policy philosophy with Obama, they pointed to an essential challenge for his nascent campaign.
While he will try to frame his understanding of international affairs as a plus, he will need to distinguish himself from a president who is deeply disliked by some hardline Republicans. Huntsman's caution in analyzing Obama's Afghanistan withdrawal suggests the difficulty of the balancing act.
"I think foreign policy and national security experience will be in great demand in years to come," he said. "The citizens of this country are going to be very interested in a president who understands the world for what it is. It's complex, it's confusing, it is uncertain and it's not going to get any better in the years to come."
Huntsman said he would likely make the final decision on running for president in about 10 days. He said most of the boxes are checked: a supportive family, confidence in raising the necessary campaign funds, a strong presence in the early primary states of New Hampshire, South Carolina and Florida.
Huntsman isn't expected to run strongly in Iowa, because of his opposition to subsidies for corn-based ethanol.
He said he wasn't afraid to defend other possibly iconoclastic positions with the Republican rank-and-file. They include his record of health care reform in Utah and support of civil unions for homosexual couples.
"Will some people hold that against me?" Huntsman asked. "It's OK. You got to be who you are and march forward. Some people will like it."