More than two months after Barack Obama placed his hand on the Bible and was sworn in as president of the United States, 11 per cent of Americans still think he is a Muslim, a poll suggested.

White evangelical Protestants and Republicans were the most likely to say Obama -- who has an Arabic middle name - was Muslim in response to the poll question: "Do you happen to know what Barack Obama's religion is?"

Nearly one in five white evangelical Protestants and 17 per cent of the Republicans who took part in the telephone poll of 1,308 adults, which was conducted by Pew Research from March 9-12, said they thought Obama was Muslim.

Fewer than half in each group - 38 per cent of white evangelicals and 46 per cent of Republicans – correctly identified him as Christian.

Even among Democrats, only 55 per cent correctly identified Obama as a Christian; seven per cent thought he was Muslim.

Poll respondents with a university degree scored highest -- 68 per cent - in correctly identifying the Democratic president's religious affiliation as Christian.

Only six per cent of university graduates said they thought he was a Muslim - less than half the 14 per cent of respondents with no more than a high school education who said the same.