The UN's envoy said the Taleban have not been invited
Speaking in Kabul, the UN special envoy, Francesc Vendrell, said the meeting would be as representative as it could be made in the short time available - but it was necessary to proceed quickly.
The Northern Alliance, which gained control of northern Afghanistan and Kabul last week, says it will attend.
But the retreating Taleban have not been invited.
Mr Vendrell said they were a regime "in the process of collapse".
"Their leadership is far too identifiable with al-Qaeda for it to be a representative interlocutor," he told the BBC.
He added that Berlin would probably be the venue for the summit, but it was not yet clear.
Meanwhile, officials from about a dozen countries are to hold discussions in Washington on Afghanistan's post-war reconstruction.
The United States and Japan will host the talks, which will begin the process of assessing Afghanistan's most pressing post-war needs, such as agriculture, water, education and mine clearance.
Correspondents say the talks are not directly linked to the negotiations over Afghanistan's political future but they are designed to show the commitment of the United States and its partners to Afghanistan's long-term future.
European Union foreign ministers have already promised to give reconstruction aid to Afghanistan, but only if the country's new government respects human rights and international law.
In other developments:
The confirmation of the Afghan conference came on Francesc Vendrell's fourth day of talks in the Afghan capital with key figures in the Northern Alliance and other tribal and faction leaders.
BBC UN correspondent Greg Barrow says it is no small achievement to decide on a date and venue for a meeting, as events on the ground have rapidly overtaken the slow pace of diplomacy.
In the south-east of Kabul, various Pashtun tribes are reportedly beginning to form a coherent, unified position on the shape of a future Afghanistan.
The BBC's Kabul correspondent, Kate Clark, says the tribes are powerful, well-organised, well armed and have the force of history behind them.
She says they are pushing a strongly peace-oriented agenda, demanding a UN-sponsored loya jirga - a grand assembly of the nation's elders - to choose a new leader for Afghanistan.
Breakthrough
The prospect of an inter-Afghan forum was given a boost after the Northern Alliance relented in its demand that talks should only take place in the Afghan capital.
The concession followed discussions in Uzbekistan between US envoy James Dobbins and Northern Alliance Foreign Minister Abdullah Abdullah.
The United States, which has led the campaign to topple the Taleban, welcomed the Northern Alliance's decision.
US Secretary of State Colin Powell said he was "very pleased" and called for talks to be held soon.
Washington and its allies fear that a government dominated by the Northern Alliance could prompt the kind of factional fighting that ripped Kabul apart in the early 1990s.
The international drive to build an interim administration has been gathering pace with the arrival in Afghanistan of Russian and British delegations.
Both Russia and Iran, which has close ties to the Northern Alliance, are planning to re-open embassies in Kabul soon.