(Image Credit: Eric Gay/AP Photo)

Former senator Rick Santorum is the most competitive Republican candidate challenging President Obama in swing state Pennsylvania, according to the latest Quinnipiac University poll.

Santorum is in a virtual tie with Obama, 44 to 45 percent, when Keystone State voters are asked to choose between the two if the presidential election were held today.  The poll has a margin of error of 2.8 points.

Meanwhile, Obama leads Mitt Romney, 46 to 40 percent, in the Pennsylvania horse race, while also beating Newt Gingrich, 50 to 37 percent.

The results of the poll, conducted March 7-12, before Tuesday night's primary results, reflect the continued appeal of Santorum in the state where he grew up, attended college, and which he later represented in Congress, pollsters say.

Obama, who won Pennsylvania by 10 points over John McCain in 2008, has meanwhile faced volatile job approval and favorability ratings in the state, signalling what will be a closely contested campaign in the fall.

Fewer than half, 47 percent, of Pennsylvania voters approve of Obama, hold favorable impressions of him and say that he deserves a second term, according to the poll.

Obama "has lackluster approval, favorability and reelection numbers in Pennsylvania, but this is his highest approval rating in a year and his best performance in months running against Mitt Romney," said Tim Malloy, assistant director of the Quinnipiac University Polling Institute.

The Obama campaign has mounted an aggressive organizing effort in Pennsylvania, operating 12 field offices, including three in the Philadelphia area.

Since April, when Obama announced his bid for a second term, Democratic volunteers have placed more than half a million phone calls to prospective voters and held 6,100 face-to-face meetings with supporters, a campaign official said.