Defence Secretary Robert Gates cautioned on Sunday that large numbers of US troops will remain in the country after a "limited" July 2011 drawdown.
Despite mounting casualties and public doubts, Gates said the US-led force was making headway in the war and Taliban insurgents would not be able to wait out American forces because a major troop withdrawal was not on the horizon.
"I think we need to reemphasise the message that we are not leaving Afghanistan in July of 2011," said Gates, referring to a deadline set by President Barack Obama for the start of a withdrawal.
"My personal opinion is that drawdowns early on will be of fairly limited numbers," he told ABC`s `This Week`.
Asked if the Taliban could simply "run out the clock" until the mid-2011 target, Gates said that he would "welcome that, because we will be there in the 19th month, and we will be there with a lot of troops."
The war has become increasingly unpopular with the American public and among Democratic lawmakers, amid a rising US death toll and a lack of confidence in Afghan President Hamid Karzai.
The United States also faces questions about whether it can win back the impoverished Afghan population from a resurgent Taliban without remaking Afghanistan in the sort of nation-building exercise it has pledged not to undertake.
Defending the US war effort, Obama told CBS`s `Early Show` that Washington`s goals were "fairly modest" and that the United States had no plans to turn Afghanistan into a Western-style democracy.
"What we`re looking to do is difficult, very difficult, but it`s a fairly modest goal, which is, don`t allow terrorists to operate from this region," he said in an interview broadcast on Sunday.
"That can be accomplished," he added. "We can stabilise Afghanistan sufficiently and we can get enough cooperation from Pakistan that we are not magnifying the threat against the homeland."
The US-led invasion of Afghanistan in the wake of the September 11, 2001 attacks ousted from power the Taliban regime and scattered Osama bin Laden and members of his al Qaeda network.
But in almost nine years since, a Taliban insurgency has become increasingly emboldened despite the presence now of almost 150,000 NATO and US troops.
Complicating the situation is a lack of faith in Karzai, who returned to power after elections generally regarded as fraudulent, and faces accusations of corruption and even ties to the drug trade.
The fragile international coalition is also seeing signs of wear -- and shrinkage.
Dutch troops ended their mission in Afghanistan on Sunday in the first significant drawdown of troops from the Afghan war.
The Netherlands` deployment began in 2006 and has cost the lives of 24 soldiers.
Obama has staked his term in office on success in the war and campaigned on a platform of devoting greater attention to the conflict.
But as the deadline he set for beginning troop withdrawals approaches, there has been little tangible progress, and key Democratic allies have said they expect US troops to begin coming home soon.
Senator John Kerry, chair of the Senate Foreign Relations Committee, said the administration needed to explain that the fight was key to US national security.
"They should be talking about... the way in which they have actually put al Qaeda under pressure," he said on CNN`s `GPS` program. "To walk away from that or to diminish that I think... history would be pretty harsh in its judgment."
Gates` comments on Sunday echoed remarks by Vice President Joe Biden who has said that as few as 2,000 troops might withdraw from Afghanistan by July 2011.
But the top Democrat in the House of Representatives, Speaker Nancy Pelosi, said on Sunday Americans wanted to see a more significant troop withdrawal.
"Well, I hope it is more than that," Pelosi told ABC, referring to the 2,000 figure offered by Biden. "I know it`s not going to be turn out the lights and let`s all go home on one day."
Democrats in Congress are increasingly anxious about the US role in Afghanistan ahead of November mid-term elections, with 102 members recently breaking ranks and voting against funding for the nearly nine-year-old war.
Last month was the deadliest yet for US troops in Afghanistan, with 66 deaths.