WASHINGTON: Afghanistan is not Iraq, US officials have been fond of saying from the first days of Barack Obama's presidency.

The difference, they said, was that one war Obama inherited, in Afghanistan, was worth fighting while the other, in Iraq, was best ended as fast as possible.

Now, Afghanistan has turned into Iraq: an inconclusive slog in which the United States cannot always tell enemy from friend. And like Iraq, Obama has concluded that Afghanistan is best put to rest.

Just as he patterned his troop "surge" in Afghanistan on a successful military strategy in Iraq, now Obama is patterning his withdrawal from Afghanistan on the Iraq template as well.

Obama and British Prime Minster David Cameron said on Wednesday that Nato forces would hand over the lead combat role to Afghanistan forces next year as the US and its allies aim to get out by the end of 2014.

It is a gradual step away from the front lines, while pushing indigenous forces to take greater and greater responsibility. It is also a gradual lowering of expectations for a country whose internal divisions and customs bewildered the Americans sent to help and where the US national security goals were often poorly understood.

"Why is it that poll numbers indicate people are interested in ending the war in Afghanistan?" a contemplative Obama asked during a news conference on Wednesday. "It's because we've been there for 10 years, and people get weary."

Obama and Cameron stressed that they will not walk out on Afghanistan, whose uneven military is not up to the task of defending the entire country. But Obama in particular seemed keen to show he does not have a tin ear.

Afghanistan is Obama's war - the one he willingly expanded and redefined as a frontal assault on Al Qaeda - but like Iraq for former President George W. Bush, the Afghanistan war is becoming political baggage.

Americans have little enthusiasm for the Afghanistan mission in this election year, and a string of violent or distasteful incidents involving US forces have refocused national attention on whether the war is achieving its goals.

The resentment and contempt each side feels for the other appears to have reached some breaking point in Afghanistan, with a rising number of killings of American troops by Afghan recruits this year. The relationship was far from perfect in Iraq, but fratricide was rare by comparison.

Six in 10 Americans see the war as not worth its costs, in a Washington Post-ABC News poll released Sunday, before news of a massacre of Afghan civilians apparently by a US soldier.

That was nearly twice the 35 per cent that said the war has been worthwhile. More Americans have opposed the war than supported it for nearly two years, but the implications are stark eight months before the presidential election.

Opposition to the war is bipartisan, and for the first time the Post-ABC poll showed more Republicans "strongly" see the war as not worth fighting as say the opposite.

"When I came into office there has been drift in the Afghanistan strategy, in part because we had spent a lot of time focusing on Iraq instead," Obama said, a bit defensively.

"Over the last three years we have refocused attention on getting Afghanistan right. Would my preference had been that we started some of that earlier? Absolutely. But that's not the cards that were dealt."

He claimed that his strategy has brought the war around the corner. He was careful not to predict victory, or use any of the traditional language of war.

"We're making progress, and I believe that we're going to be able to make our - achieve our - objectives in 2014," he said.

In the same poll, a majority of Americans said they think a majority of Afghans are opposed to what the Nato-led mission is trying to accomplish in their country. A majority also said the United States should withdraw troops even before the Afghan army is able to stand on its own.

Obama used Cameron's visit to endorse a shift toward a back seat advisory role for US forces in Afghanistan next year, although the war will go on for another year or more. That follows the model of Iraq in 2010, when US forces symbolically pulled back and placed their Iraqi hosts in charge.

He said any sudden drawdown of US forces is unlikely in Afghanistan. If he follows the Iraq model, the reduction will be steady and permanent, and taken with an absence of fanfare. The United States has roughly 90,000 troops in Afghanistan. Obama plans to drop that number to 68,000 by late September but has offered no specific withdrawal plan after that. Britain has the second-largest force in Afghanistan with about 9,500 troops.

Britain is pulling about 500 troops from Afghanistan by the end of 2012, leaving around 9,000 personnel, mainly based in the centre of the southern Helmand province.

Officials in London have already cautioned against public hopes that large numbers of troops will be able to leave in the first half of 2013.

Cameron emphasised the scaling back of ambitions since 2001, acknowledging "we will not build a perfect Afghanistan" by the time international forces withdraw from the country. Where his predecessors hailed efforts to improve education, health care and governance, Cameron took office in 2010 saying he would accelerate the training of Afghan troops and police.

He said Britain and the US were now "in the final phases of our military mission," but - like Obama - did not suggest the timetable for British troops to withdraw would be accelerated.

Like Iraq, the Afghanistan war has been given an artificial expiration date. US and Nato forces will close out their current mission and leave by the end of 2014. The surge forces Obama added will be gone by the end of September.

Obama came into office with an end date in Iraq already set by his predecessor - Dec 31, 2011. Obama stuck to that schedule but added his own "end of combat" date - Aug 31, 2010. That gave US forces the remaining months to hand off security control to the Iraqis. By the end, American casualties were rare and US troops often had little to do.

The US and its allies have not yet set a precise "end of combat" date in Afghanistan, although the mid-2013 target Obama articulated on Wednesday looks to be the same thing. That calendar would give approximately the same amount of time - roughly 15 months - for US and allied forces to complete the security handoff to Afghan forces.

Like Iraq, fighting is sure to continue in Afghanistan after the transition to an "advise and assist" role for US forces and after US forces quit the country altogether. The relationship between the Afghan security forces and the Afghan government is even more tenuous than it was in Iraq, making it more difficult to ensure that security will hold up after the Americans leave.

By the time the US forces switched to the advisory role in Iraq, the back of the insurgency had been broken. The same cannot be said for the Taliban-led insurgency in Afghanistan, which causes most of the US casualties and functions as the main enemy even if Obama's preferred opponent is the Al Qaeda terror network the Taliban once harboured.-AP