A new poll has found Australians' attitudes towards the United States are improving, but they are becoming more concerned about China's growing influence.

The Lowy Institute surveyed 1,000 Australians about their views on foreign policy issues.

More than three-quarters said Australia's alliance with the United States was fairly important or very important, the highest level of support since the annual survey began in 2005.

But Australians are less happy about the rise of China, with a majority saying Australia should join with other countries in limiting China's influence.

Last year, respondents were evenly divided over whether Australia should continue its military involvement in Afghanistan, but 56 per cent are now opposed.

The poll also found Australians are overwhelmingly in favour of Barack Obama over John McCain as the next US president, by a margin of almost 5:1.