Disapproval of President Bush was hurting the Republican Santorum, said the poll by Temple University and the Philadelphia Inquirer, which surveyed 666 likely voters in telephone interviews.

"Some of the reason Santorum trails is due to national forces, but it's not the whole story," Michael Hagen, pollster and associate professor of political science at Temple University, told the Inquirer. "It is also about his candidacy and his personality."

Casey led among independent voters, 49 percent to 35 percent, the poll said. Three percent of respondents favored Green Party candidate Carl Romanelli, and 8 percent said they were undecided.

The poll findings are practically identical to a Rasmussen poll released last week that found Casey leading Santorum 49 to 39 percent. They differ, however, from several polls released last month. A poll commissioned by the Democratic Senatorial Campaign Committee found Casey leading Santorum 14 percentage points, or 51 to 37 percent. The findings also differ from a Quinnipiac University poll in August that found Casey leading Santorum by only 6 percentage points, 48 percent to 42 percent.