The official, in an interview with The Associated Press, also added that the president is prepared to accept some Taliban involvement in Afghanistan's political future, reiterating what Obama said in March.
The assessment comes from an official who has been involved in the president's discussions with his war council about Afghanistan strategy.
Aides say the president's final decision on Afghanistan strategy and troop levels is still at least two weeks away, but the emerging thinking suggests he would be unlikely to favor a large military ramp-up of the kind being advocated by his top commander in Afghanistan.
McChrystal's troop request is said to include a range of options, from adding as few as 10,000 combat troops to -- the general's strong preference -- as many as 40,000.
Obama's developing strategy on the Taliban will "not tolerate their return to power," the senior official said. But the U.S. would fight only to keep the Taliban from retaking control of Afghanistan's central government -- something it is now far from being capable of -- and from giving renewed sanctuary in Afghanistan to Al-Qaeda, the official said.
Recognizing the U.S. can neither win in Afghanistan nor succeed more broadly against Al Qaeda without Pakistan's cooperation, Obama's war council is weighing a new role for Pakistan in the 8-year-old struggle in the region.
Obama's national security team marked the war's eighth anniversary on Wednesday with a three-hour session in a secure room in the White House basement. The focus on Pakistan, the suspected hiding place of Usama bin Laden and other Al Qaeda terrorists as well as Taliban leaders, could provide a hint into the president's leanings.
Members of the president's national security team argued that the Taliban in Afghanistan do not pose a direct threat to the U.S., officials told The New York Times. It was unclear if everyone in the war council accepted the premise.
Obama and some of his key aides are increasingly pointing to recent successes against Al Qaeda through targeted missile strikes and raids in Pakistan but also in Somalia and elsewhere. Obama said Tuesday that Al Qaeda has "lost operational capacity" as a result.
Vice President Biden has argued against increasing the number of U.S. troops in Afghanistan, saying Pakistan poses the greater threat, but Defense Secretary Robert Gates and Secretary of State Hillary Clinton have both warned that the Taliban and Al Qaeda remain connected. If the Taliban were to regain control of large parts of Afghanistan, the country could serve as a sanctuary for Al Qaeda fighters, the have advisors said.
A State Department spokesman said Thursday that Clinton believes the Taliban and Al Qaeda are both a threat and the U.S. is fighting the whole idea of killing in the name of religious extremism.
In Pakistan, though, the government has shown new willingness to battle extremists, with most believed to be operating from the largely ungoverned terrain along the border with Afghanistan. But these operations, as well as the strikes by unmanned U.S. aircraft, continue to stoke controversy throughout the country, causing problems for the already weak U.S.-backed civilian government.
Obama planned sessions Thursday with Biden and Clinton in the Oval Office to continue the intense discussion about the increasingly unpopular war in Afghanistan. The White House scheduled another, larger war council session -- a fifth of five announced -- for Friday, when the focus may finally shift to just how many additional troops would be needed to execute Obama's vision for a war he inherited but now must execute.
The White House revealed that Obama has in hand -- and has for nearly a week -- the troop request prepared by the top U.S. commander in Afghanistan, Gen. Stanley McChrystal. It is said to include a range of options, from adding as few as 10,000 combat troops to -- McChrystal's strong preference -- as many as 40,000.
White House press secretary Robert Gibbs said Obama asked for McChrystal's request last week before he flew to Copenhagen to lobby for Chicago's bid to host the Olympics and meet with the general on the sidelines. The numbers could become the focus of concentrated White House attention as soon as Friday, Gibbs said.
While Gibbs had said previously that Obama didn't want to see the request until he had determined the strategy, aides said the president decided it had simply become absurd to wait to read it given the high-profile debate.
McChrystal's recommended approach calls for additional troops in Afghanistan for a counterinsurgency campaign to defeat the Taliban, build up the central government and deny Al Qaeda a haven. McChrystal, whose plan is somewhat reminiscent of President George W. Bush's Iraq troop surge in 2008, says extra troops -- preferably at the higher end of his option range -- are crucial to turn around a war that will probably be won or lost over the next 12 months.
On roughly the opposite end of the spectrum, an alternative favored most prominently by Biden would keep the American force in Afghanistan around the 68,000 already authorized, including the 21,000 extra troops Obama ordered earlier this year, but increase the use of surgical strikes with unmanned Predator drones and special forces.
Shrinking the number of troops in Afghanistan and turning the effort into a narrow counterterror campaign is not on the table, officials say, and neither is drastically ballooning the footprint.
In weighing whether to follow McChrystal or Biden or land somewhere in between, Obama faces a stern test and difficult politics.
Many lawmakers from his own Democratic Party, aware of rising anti-war sentiment in their ranks and the war protests that have dotted Washington this week, do not want to see additional U.S. troops sent to Afghanistan. According to a new Associated Press-GfK poll, public support for the war has dropped to 40 percent from 44 percent in July.
Republicans, meanwhile, are urging Obama to heed the military commanders' calls soon or risk failure.
With this and Americans' dwindling patience in mind, Obama is engaged in a methodical review of how to overhaul the war.
The Associated Press contributed to this report.