WASHINGTON (AFP) - Democratic White House candidate Barack Obama has pulled ahead of Republican John McCain in the latest Gallup voter opinion survey, published Tuesday in USA Today.

Obama lead McCain 47 to 44 percent, in a reversal from Gallup's findings a month ago, which saw McCain ahead of Obama 47 to 45 percent.

Both leads are within the poll's four point margin of error.

A matchup pitting Hillary Clinton against McCain saw the former first lady with a sharper advantage of 49 percent versus 43 for the presumptive Republican nominee, Gallup found.

Obama was favored to win Tuesday's final two primaries in Montana and South Dakota and also to clinch the Democratic nomination, possibly in the same day.

The poll found that 58 percent of Americans have a positive image of Obama, 56 view McCain favorably and 54 have a good opinion of Clinton.

But President George W. Bush's approval rating was just 28 percent.

And the poll depicted Americans as pessimistic about their buying power, with 55 percent saying they are worse off now than they were a year ago and just 26 percent saying the reverse.

Americans have not been so gloomy since 1976, Gallup said, adding that such sentiment generally leads voters to oust whatever political party is currently in the White House.