After pledging to speed up France's pullout from Afghanistan, incoming president Francois Hollande will soon have to reassure NATO allies about his decision to end combat earlier than planned.

Hollande made a campaign promise to start bringing 3,300 French soldiers home this year, ending his country's combat role two years earlier than NATO's carefully crafted plan to fully hand security control to Afghans by 2014.

"I believe that, without taking any risks for our troops, it is the right thing to withdraw our combat troops by the end of 2012," Hollande said last week.

The Socialist leader will bring this message to fellow NATO leaders when they meet at a summit hosted by US President Barack Obama in Chicago on May 20-21, just days after Hollande's oath of office.

NATO military officials say the alliance had already made contingency plans in the event Hollande defeated right-wing incumbent President Nicolas Sarkozy.

Nevertheless, a diplomat acknowledged that the new leader's stance "was not warmly welcomed" at alliance headquarters.

Afghan officials downplayed Hollande's pledge, insisting that Afghan forces will be ready to take over security responsibility in 2013 and doubting that France has enough time to complete a withdrawal by the end of this year anyway.

But the early French pullout challenges NATO assurances that there would be no "rush to the exit" in Afghanistan, even though the war is unpopular in the West after a decade of fighting that has killed almost 3,000 foreign troops.

In Chicago, NATO wants to show a united front, repeating its "in together, out together" mantra as it fine-tunes the final phase of a mission that has yet to defeat the Taliban despite the presence of 130,000 foreign troops.

"Mr Hollande made clear during the election campaign that any decisions on the next stage will be taken in consultation with NATO allies and that's exactly why all NATO leaders are meeting in Chicago," said alliance spokeswoman Oana Lungescu, stressing that the 2014 timeline would be reaffirmed.

Canada and the Netherlands have already switched to training missions while Australian Prime Minister Julia Gillard indicated last month that her troops could begin leaving as early as next year.

Sarkozy himself had surprised some allies by deciding earlier this year to end France's combat mission in 2013 after four French troops were killed by a rogue Afghan soldier.

Francois Heisbourg, special advisor at the Foundation for Strategic Research in Paris, said the NATO alliance wanted to avoid any drama as it attempted a smooth withdrawal from Afghanistan, even if success was uncertain in the end.

"Everybody is aware of this, and NATO has no interest in creating a controversy" with Hollande, he said. "The priority is to avoid giving the impression of a disorderly withdrawal."

A senior NATO military official said the Afghan transition would be "fairly well managed" despite Hollande's plan, as commanders had already anticipated the possibility that he might be elected and prepared accordingly.

NATO military planners "are paying attention to various nations and political situations all the time," the official said.

A senior Afghan defence official doubted whether an early withdrawal was feasible since there are only seven months left in the year for a complex withdrawal operation.

"From a military point of view I think it's not practical to withdraw troops within what's left of 2012," the official said on condition of anonymity.

It generally takes between 12 and 18 months for foreign troops to hand control of a region to Afghan soldiers.

The French military has to bring home 1,500 containers filled with equipment as well as 1,200 vehicles, including 500 heavily-armoured vehicles and 14 helicopters.

"I think it was rather an election campaign promise than a practical decision," the Afghan official said. "They won't withdraw this year."