The independent Quinnipiac University poll found Clinton leads Obama 51 percent to 44 percent among likely Democratic primary voters, compared to 50 percent to 44 percent last week.

Among white Democrats, Clinton leads Obama 57 percent to 38 percent, while blacks support Obama over Clinton, 84 percent to 10 percent, the poll found.

"Pennsylvania voters apparently made up their minds a couple of weeks ago and nothing has happened since to change them. An extraordinary turnout effort by Senator Barack Obama's campaign could snatch this victory

from Senator Hillary Clinton, but that does not appear likely," said Clay Richards, assistant director of the Quinnipiac University Polling Institute.

The poll, conducted from April 18 to April 20, surveyed 1,027 Pennsylvania likely Democratic primary voters. The poll has a margin of error of plus or minus 3.1 percentage points.