The Quinnipiac University survey also found that more Americans disapprove, by 50 percent to 44 percent, of the job President Barack Obama is doing - although more people than not approve of the way he has handled foreign policy, including his management of thorny US relations with Tehran.
Some 55 percent of respondents said the United States should not take immediate military action against Iran, with 36 percent in favour.
The number in favour of using force increases to 50 per cent however if sanctions fail, with 38 percent against.
"Americans are very concerned about the development of an Iranian nuclear program and don't think the current policy of economic sanctions is effective," said Peter Brown, assistant director of the Quinnipiac Polling Institute.
"Voters are not yet to the point that they want the US military to stop it, but 50 per cent say that if the sanctions eventually prove to be ineffective then they would support the use of force," he added.
The Quinnipiac survey also found that 46 per cent of voters believed the United States should support Israel if it attacks Iran, with six per cent saying Washington should oppose Israeli action and 44 percent saying the US should stay neutral.
The poll found that two in three Americans (60 per cent versus 33 per cent) believe economic sanctions against Iran are currently ineffective.
While voters said, but a margin of 48 per cent to 45 per cent that he does not deserve a second term, they felt more charitably towards him on foreign policy, which garnered 49 pe rcent approval against 45 per cent disapproval.
The president's handling of Iran meanwhile won the support of 48 per cent of respondents, compared to 45 percent who disapproved.
This week, Britain, Canada and the United State announced new sanctions on Iran, citing a report by the United Nations (UN) atomic energy watchdog this month suggesting Tehran was researching nuclear weapons.
Britain said it was "ceasing all contact" between its financial system and that of Iran. The United States and Canada said they would also clamp down on the sector, including on Iran's central bank.
The Quinnipiac poll was conducted by telephone among 2,552 registered voters between November 14 and November 20 and had a 1.9 per cent margin of error.