"I have offered London as a venue in the new year ... I want that conference to chart a comprehensive political framework within which the military strategy can be accomplished.
"It should identify a process for transferring district by district to full Afghan control and if at all possible set a timetable for transfer starting in 2010.
"It is only when the Afghans are able to defend the security of their own people and deny the territory of Afghanistan as a base for terrorists, that our strategy of 'Afghanisation' will have succeeded and our troops can come home."
Brown conceded that international terrorism remained the biggest threat to Britain's national security, singling out al-Qaeda.
|Brown said the UK was in Afghanistan because al-Qaeda would thrive otherwise [AFP]
"We are in Afghanistan because we judge that if the Taliban regained power, al-Qaeda and other terrorist groups would once more have an environment in which they could operate," he said.
But he said that al-Qaeda, which once operated from within Afghanistan under the protection of the Taliban, has been pushed into the border area with Pakistan.
Brown said al-Qaeda was still taking strength from "an extensive recruitment network across Africa the Middle East, Western Europe, and in the UK", and called for Britons to be "patriotic and internationalist" in their mindset.
"As a nation we have every reason to be optimistic about our prospects: confident in our alliances, faithful to our values and determined as progressive pioneers to shape the world to come."
The international military mission in Afghanistan has become increasingly unpopular insome of the 42 countries that have sent troops to the 100,000-strong foreign contingent in Afghanistan.
Brown is under pressure from the electorate as British casualties from the war increase.
Opinion polls show an increasing majority of Britons want the country's 9,000 troops to pull out of Afghanistan within 12 months.
Five soldiers were shot dead earlier this month by a "rogue" Afghan policeman they were helping to train, marking a low point of Britain's involvement in the eight-year conflict.
The Daily Mail, a British newspaper, reported on Tuesday that a new British army field manual said that soldiers should buy off potential Taliban recruits in Afghanistan with cash.
Western leaders have insisted that Hamid Karzai, the Afghan president, should tackle corruption as a condition for support in his second term, which begins on Thursday.