'A few years' needed
But Conway, who is expected to retire by the end of October, as head of the marine corps, said he believed marines would not be in a position to withdraw from the fight in southern Afghanistan for years.
A "turnover" to Afghan forces in key southern provinces will not be possible for "a few years," he said.
Conway's unusually blunt assessment is the latest sign from US military leaders that a major troop withdrawal remained a long way off, despite a mid-2011 deadline set by Barack Obama, the US president, for the start of a pullout.
"I honestly think it will be a few years before conditions on the ground are such that turnover will be possible for us," he said, referring to troops deployed in the provinces of Helmand and Kandahar.
Conway acknowledged that public support for the US mission was declining but warned of the risks of any early withdrawal.
"I sense our country is increasingly growing tired of the war," he said.
Conway, quoting one of his own commanders, told reporters: "We can either lose fast or win slow."
The last units of a surge of 30,000 reinforcements had only arrived in Afghanistan this month, he said.
"We have the momentum. We have the initiative, but that's different from declaring that security conditions are changed dramatically in Helmand," he said.
The general said the administration needed to do a better job of explaining the mission to Americans and the importance of preventing al-Qaeda from regaining a foothold in the country.
Asked to specify how many years US forces might have to stay in southern Afghanistan, Conway said he could not offer a forecast.
However, he said the Kabul government's efforts to promote reconciliation with the Taliban could dramatically alter the conflict and the Nato-led mission.
|Conway says efforts to promote reconciliation with Taliban "could be a game-changer" [AFP]
An armed uprising against the Taliban, similar to Sunni tribes taking on al-Qaeda in Iraq, was unlikely in Afghanistan, but "reconciliation could be a game-changer," he said.
Conway spoke a day after the US general in charge of training Afghan forces played down prospects for a major transfer of security duties to the Afghans for at least another year, three months after the July 2011 target date.
Robert Gates, the US defence secretary, has suggested any troop reduction after mid-2011 would be modest, but he has also held out the possibility of Afghan troops taking over security in some districts by the end of the year.
With casualties mounting, Obama's fellow Democrats in Congress are increasingly anxious over the course of the nearly nine-year-old war, and many want to see a substantial reduction in the US commitment after mid-2011.
On Tuesday, the Nato-led International Security Assistance Force (Isaf) said one of its soldiers was killed while fighting Taliban-linked fighters in the south.
The death brings to 457 the toll of international soldiers killed in the Afghan war so far this year, compared with 520 for the whole of last year.
Twelve international soldiers have been killed since Saturday, according to an AFP tally based on the icasualties.org website, seven of them Americans.