Obama, who still leads Hillary Clinton in the race for the Democratic presidential nomination, however finds himself facing plummeting numbers.

According to New York Times/CBS survey released on Wednesday, 51 per cent of Democratic primary voters now expect Obama to win the nomination, down from 69 a month ago.

At least 48 per cent of Democrats now say Obama is the candidate with the best chance of beating Senator John McCain, the presumptive Republican nominee, down from 56 per cent a month ago.

The poll, which was conducted April 25-29 largely before Obama's news conference on Tuesday in which he denounced his former pastor, the Rev. Jeremiah A Wright Jr, may not have fully captured the impact of the controversy or Obama's response.

The poll shows the Illinois Senator still holds an edge over his rival Hillary Clinton on several key measures. As many as 46 per cent of the Democratic primary voters said he remained their choice for the nomination, while 38 per cent preferred Clinton, down from 43 per cent last month.

Clinton has further lost support among men in recent weeks, it added.