After a decade in Afghanistan, NATO leaders gather for a key summit Sunday hoping for a show of unity in the final two years of combat -- even though allies are eager to bring troops home.

US President Barack Obama hosts two days of talks in Chicago, witht the allies hoping to demonstrate a renewed commitment to Afghanistan as protesters threaten to flood the streets to denounce a war which has killed thousands of troops and civilians.

Obama and his fellow leaders will take other key decisions for NATO's future, activating the first part of a missile shield for Europe and announcing a slew of military cooperation projects to cope with mounting austerity.

Afghanistan however will be the centrepiece of a summit billed as the biggest in NATO's history, with some 60 nations and international organisations invited, including Afghan President Hamid Karzai.

"I look forward to meeting with President Karzai and my fellow leaders in Chicago to discuss these critical steps that will strengthen Afghan sovereignty while responsibly winding down the war," Obama said on Sunday.

The US president said world leaders would discuss how to "effectively advance" the transition process, but the strategy faces growing public impatience as well as French plans to speed up its own withdrawal.

NATO is gradually handing control of security to Afghan forces, with the aim of giving them the lead nationwide next year and drawing a path home for foreign combat troops by the end of 2014.

An orderly withdrawal of the 130,000 US-led troops is vital for Obama, who wants to show voters ahead of a tough November election that he can successfully end combat in Afghanistan after withdrawing from Iraq last year.

But the new French president, Socialist Francois Hollande, is set to make waves during his first US trip since taking office on Tuesday by telling allies that he will bring troops home by the end of 2012 instead of next year.

"At this stage we're shuttling out of Afghanistan as fast as we can or even faster," Nick Witney, a defence expert at the European Council on Foreign Relations, told AFP. "And Afghanistan is facing an empty future."

NATO leaders, he said, "will try to create the impression that everyone's timetable fits the alliance pattern."

Hollande is not the first leader to push for an early withdrawal.

Canada and the Netherlands have already switched to training missions while Australian Prime Minister Julia Gillard indicated that her troops could leave next year, although her government later said they would stay through 2014.

But NATO Secretary General Anders Fogh Rasmussen insists that the summit will cement the alliance's mantra of "in together, out together."

The mission has been plagued by other challenges, including growing cases of Afghan soldiers turning their guns on their NATO allies and Afghan anger over civilian deaths caused by alliance operations.

After 2014, a number of foreign military trainers are expected to stay behind to ensure that Afghanistan's security forces are able to prevent the resilient Taliban insurgency from forcing their way back to power.

Karzai gave withdrawal plans a boost this week, announcing that more than 300,000 Afghan forces were taking control of 11 more provinces, bringing 75 percent of the population under their protection.

The leaders will debate the size and funding of the Afghan army after 2014, estimated to cost $4.1 billion a year, with the United States expected to foot half the bill while hoping the international community will pay the rest.

Governments, however, are feeling the pinch as Europe's debt crisis forces budget cuts across the board. The United States, which accounts for 75 percent of NATO military spending, has pressed Europeans to pull their own weight.

To cope with the austerity, NATO will announce more than 20 joint projects to pool military hardware as part of a "Smart Defence" initiative to ensure the alliance spends scarce resources wisely.

NATO has touted a planned US-led missile shield for Europe as a shining example of military cooperation.

A first step to the shield will be the announcement at the summit of an "interim capability" putting US warships armed with missile interceptors in the Mediterranean, and a radar system based in Turkey under NATO command.

The system has angered former Cold War foe Russia, which fears that it would undermine its nuclear deterrent, and President Vladimir Putin decided not to attended the talks.