The poll appears on the day that President Barack Obama is expected to declare that his strategy in Afghanistan and Pakistan is on track. Dissatisfaction with the war has risen seven points since July, according to ABC News.
On a cost-benefit basis, only 34 per cent of those polled believe the war has been worth fighting, down nine points and setting a new low.
"Negative views of the war for the first time are at the level of those recorded for the war in Iraq, whose unpopularity dragged (former US president) George W Bush to historic lows in approval across his second term," ABC News said.
Obama got mixed reviews for handling the war effort: 45 per cent of those surveyed approve of Obama's work on Afghanistan, while 46 per cent disapprove.
Fifty-four per cent of Americans also support Obama's pledge to start withdrawing US forces from Afghanistan in mid-2011, up by 15 points since it was announced one year ago.
The telephone poll was conducted by Langer Research Associates between December 9-12 among a random sample of 1,001 US adults. It has a 3.5-point error margin.
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