The troops will be in place by Saturday
The troops, from 40 Commando, will deploy to Bagram airbase from HMS Fearless, in readiness for peacekeeping operations in Afghanistan, a spokesman said.
Defence Secretary Geoff Hoon will make a statement on the make-up of the deployment in the Commons on Wednesday.
The marines will form the lead element of a multinational peacekeeping force, expected to number up to 5,000, to help secure Afghanistan's future.
Downing Street refused to confirm that a decision had been taken on deploying British ground troops.
But the prime minister's official spokesman said soldiers "could" be on the ground by the weekend, if a decision was made.
Peacekeeping talks Military advisers from 16 countries that have agreed to contribute troops to the force will meet in London on Wednesday for further talks.
Meanwhile efforts to agree the sensitive issue of the size and powers of the international deployment continue.
Prime Minister Tony Blair has said Britain is prepared to lead the force and commit up to 1,500 troops.
Major General John McColl is on his way back to the UK after negotiating with Afghanistan's incoming administration over the peacekeeping operation.
Defence minister Mohammed Fahim has resisted any international military presence beyond a relatively small force of around 1,000 troops.
Downing Street said nations participating in Wednesday's conference included France, Germany, Spain, Argentina, Australia, New Zealand, Canada, Turkey, Jordan, Malaysia, the Czech Republic and the United States.
Fears calmed
The announcement on the deployment of marines came as Mr Hoon sought to alleviate fears among senior military figures that UK involvement in Afghan peacekeeping operations would overstretch the armed forces.
Speaking in the House of Lords, Former defence chief of staff Lord Guthrie said Britain might be taking on too much by deploying large numbers in the troubled country.
But Mr Hoon told the BBC any UK deployment in Afghanistan would be "time limited" lasting just a "small number of months".
The marines are set to be in place by 22 December when the interim Afghan administration is due to take power.
Mr Blair has said a stabilisation force was a "critical" part of the Bonn agreement which set up that interim administration.