Survey results issued yesterday showed US public support sliding for the war as Afghans voted in a pivotal election amid speculation that the top United States commander in Afghanistan, General Stanley McChrystal, will request more troops.

Asked if the war was worth fighting, 51 per cent said it was not, while 47 per cent endorsed the mission, the Washington Post-ABC News poll said.

Last month, a narrow majority backed the war as worthwhile.

Only 24 per cent said more US forces should be deployed, while 27 per cent said the troop levels should be kept the same and 45 per cent said the troop commitment should be reduced.

In January, only 29 per cent said the number of troops should be cut back.

The poll, carried out between August 13-17, showed Americans had doubts that the elections would result in an effective Afghan government.

Only 31 per cent said they were confident that the vote would produce a government that could rule effectively while a 64 per cent majority said they were not confident of such an outcome.

Despite signs of public anxiety, a majority of 60 per cent approved of how President Barack Obama had handled the war, while 33 per cent disapproved, the poll said.

Opinion was divided as to whether the US was winning the war, with 42 per cent saying America was winning while 36 per cent said the US was losing.

Opposition to the war had grown among those who form Mr Obama's core of support: liberals and Democrats, the survey said.

Almost two-thirds of staunch Democrats now felt ''strongly'' that the war was not worth fighting, it said.

And support for the war among voters who identified themselves as liberals had dropped dramatically. Strong approval for Mr Obama's approach to the war among liberals had fallen 20 percentage points and 63 per cent of liberals wanted troop levels reduced.