The lead coincided with controversy caused by Obama's relations with his long-time Chicago pastor, Jeremiah Wright, who has been heard criticizing the US government for its "racist policies".

Democratic presidential candidate Senator Barack Obama speaks to supporters during a campaign stop at the University of Charleston in Charleston, West Virginia, March 20, 2008. (Xinhua/Reuters Photo) 

Although Obama made a major speech on Tuesday on the race issue, hoping to move past the controversy, the polling numbers have not shown immediate benefit for him, Gallup said.

However, Obama still maintained a lead in the number of delegates who would vote for him at the nomination convention over Clinton by 1,621 to 1,479.

The survey also indicated that voters moved closer to Republican presumptive presidential nominee John McCain, who has a lead of 47 percent to 43 percent over Obama and holds an edge of 48 percent to 45 percent over Clinton.

(Xinhua News Agency March 21, 2008)