Barack Obama has said the US is "on track" to achieve its goals in Afghanistan, following publication of the US annual strategy review.
The review said al-Qaeda's leadership was at its weakest since 2001.
And it added that the US had made enough progress to start a "responsible reduction" of forces in July 2011.
Mr Obama said US forces and their allies were clearing more areas from Taliban control, but warned that the gains were still fragile.
"This continues to be a very difficult endeavour," Mr Obama said. But he added that US would remain "relentless" in pursuit of al-Qaeda.
The review says the surge in foreign troops has succeeded in halting Taliban momentum in much of the country, but BBC correspondents say the bigger picture is of an insurgency fighting to the death in Helmand and Kandahar and expanding in places like Ghazni and Kunduz.
The US plans to end combat operations in 2014 and transfer responsibility for the country's affairs to Afghans.
The White House review comes at a time when civilian casualties are at their highest since the US-led invasion of 2001. This year has also been the bloodiest for foreign troops since 2001, with the US taking the brunt of the casualties.
At the White House, Mr Obama said he wanted to remind Americans that America was in Afghanistan to disrupt, dismantle and defeat al-Qaeda.
"It was Afghanistan where al-Qaeda plotted the 9/11 attacks that murdered 3,000 innocent people. It is the tribal regions along the Afghan-Pakistan border from which terrorists have launched more attacks against our homeland and our allies.
"And if an even wider insurgency were to engulf Afghanistan, that would give al-Qaeda even more space to plan these attacks."
He said al-Qaeda's leadership was "hunkered down", but said it would continue to take time to defeat an enemy he described as "ruthless and resilient".
'Gains remain fragile'
Mr Obama spoke hours after the White House released a five-page summary of a review of the war strategy in Pakistan and Afghanistan.
The review by White House national security staff said al-Qaeda's senior leadership, based in Pakistan, was weaker and under more pressure than at any other point since it fled Afghanistan in 2001 following the initial US invasion.
It said Washington is "laying the foundation for a strategic partnership [with Pakistan] based on mutual respect and trust" and said Pakistan had made progress in tackling al-Qaeda's "safe havens" but admitted the alliance remains "uneven".
The review continued: "In Afghanistan, the momentum achieved by the Taliban in recent years has been arrested in much of the country and reversed in some key areas, although these gains remain fragile and reversible.
"While the strategy is showing progress across all three assessed areas of al-Qaeda, Pakistan and Afghanistan, the challenge remains to make our gains durable and sustainable."
The review comes as Americans' patience with the war in Afghanistan appears to be waning. According to a new poll by ABC news and the Washington Post, 60% of Americans say the war has not been worth fighting. That is up seven points just since July.
Meanwhile, 14 people - many reportedly members of a family travelling to a wedding - were killed when a roadside bomb struck. A national security officer attributed the attack to the Taliban.