The Obama campaign is hoping to use its network of supporters in Pennsylvania to collect dirt on Rick Santorum, whose surging candidacy has upended the Republican presidential race.

The campaign sent an e-mail asking Obama’s Keystone State supporters to submit their most damning “recollections” of Santorum, who served as a congressman and a senator from Pennsylvania for 16 years before losing reelection in 2006.

Santorum became a favorite target of liberals with his passionate statements against homosexuality and abortion, but despite his deeply conservative take on social issues, he has shown some ability to connect with blue-collar voters in the GOP presidential race — voters who have been a hard sell for former Massachusetts governor Mitt Romney and could be crucial in a general election.

“Folks across the country are just starting to learn about Rick Santorum as he enjoys his newfound wave of popularity,” says the note, which was signed by Bill Hyers, Pennsylvania state director for Obama for America. “But people here have known him for some time. . . . And it’s on us to make sure the rest of the country sees Rick Santorum’s true colors.”

The effort represents a shift for the Obama campaign, which thus far has aimed most of its attacks at front-runner Romney. But the former Pennsylvania senator has shown some sustained momentum lately, especially in Michigan, which will hold its primary Feb. 28. Romney was long favored to win the state because he grew up there and his father served as its governor.

Obama campaign officials have not yet disclosed what they will do with the collected comments, but it is part of the campaign’s national “Truth Team” effort, which uses its network of grass-roots supporters to help highlight the president’s accomplishments, defend him against attacks and spotlight controversial or hypocritical comments made by his Republican opponents. On Thursday, the campaign announced the creation of a Pennsylvania-specific “Truth Team.”