Barack Obama To Announce Withdrawal Of 33,000 Troops

In keeping with agreements reached with David Cameron, he is also likely to set out a path to ending the US combat role by the end of 2014 and withdrawing the majority of the current 100,000 US deployment.

In a national address from the White House Mr Obama will warn that it is in the long term interests of the United States to maintain a sizeable troop presence on the ground to provide training and supervision to the Afghan army.

It is expected that 10,000 of the "surge" forces will be pulled out this year, half next month and half in the winter, though White House aides said the numbers had not been finalised.

That would go against the wishes of Gen David Petraeus, the US commander in Afghanistan, who has favoured withdrawing only 5,000 in 2011.

But it would represent a compromise between the views of the military and civilian advisers in the White House and members of Congress who favour a speedier exit. It would also give the military close to its maximum capacity for this year's and next year's current warm weather fighting season.

Despite advocating a more gradual reduction in forces Robert Gates, the outgoing Defence Secretary, has admitted that "the drawdown must be politically credible here at home."

Mr Obama has weighed his options amid rising dissatisfaction with the war among the public, which in November 2012 will decide whether or not to give him a second term. Polls have shown that more than 60 per cent now oppose the war, which has claimed 1,629 American lives since the October 2001 invasion to oust the Taliban regime and its al-Qaeda allies.

A rare alliance of anti-war liberal Democrats and Republicans worried about the $2 billion-a-week cost of the US deployment has put further pressure on the White House.

Twenty-seven senators from both parties sent Mr Obama a letter last week pressing for a shift in Afghanistan strategy and major troop cuts.

"Given our successes, it is the right moment to initiate a sizeable and sustained reduction in forces, with the goal of steadily redeploying all regular combat troops," they wrote. "The costs of prolonging the war far outweigh the benefits."

The death of Osama bin Laden at the hands of US Navy Seals may have been a boost for the president, but it weakened a major justification for the war, which was to "dismantle, disrupt and strategically defeat" al-Qaeda.

Analysts said the success of the Mr Obama's timetable will depend in part on the success of reconciliation talks with elements of the Taliban which are in the preliminary stages.

To maintain the military pressure to bring the insurgents to the table, it is expected that the focus of counter-insurgency operations will shift from the south, where considerable gains have been made, to the east, where the Taliban remains unchallenged in many places.

That would involve Nato forces handing over much of the responsibility for security in recently volatile areas to Afghan forces whose readiness remains questionable.

"Are they ready? The answer is probably and maybe," said Richard Fontaine, a senior fellow and the Centre for a New American Security. "At the end of the day you don't know until you start doing it, which is why you do it progressively."

David Cameron has said that 450 British personnel will leave Afghanistan this summer, although Nick Harvey, the armed forces minister, said that it would be “presumptuous” to think that Britain would take its lead from the US, adding that troops would be withdrawn based on conditions on the ground.