Alex Brandon/Associated Press

Former Senator Rick Santorum of Pennsylvania announced on Wednesday that he had opened a presidential fund-raising committee, a step that allows him to explore a bid for the Republican presidential nomination.

Mr. Santorum, who for months has been introducing himself to voters in Iowa, New Hampshire and South Carolina, filed papers with the Internal Revenue Service that permit him to solicit contributors. He is the fourth potential Republican candidate to start raising money for a presidential bid.

He made his announcement in an interview on Fox News Channel’s “On the Record” program on Wednesday evening. (Earlier this year, Fox News Channel suspended him from his role as a contributor for the network while he made a decision about his political future.)

“The test for me is whether we can raise the money that’s necessary, so I’m going to set up a committee,” Mr. Santorum said. “We’re going to determine over the next few weeks as to whether the resources are going to be there to do it.”

Mr. Santorum has been aggressively reaching out to social conservatives in early voting states. He received an initial showing of support by winning a straw poll last week at a Republican convention in Greenville County, the largest county in South Carolina.

He served two terms in the Senate, where he was one of the Republican Party’s most outspoken critics of abortion rights and stem cell research. He lost his bid for a third term in 2006 to Senator Bob Casey, Democrat of Pennsylvania.

As he announced his presidential fund-raising committee on Wednesday, Mr. Santorum also presented a new campaign slogan on his Web site: “Fighting to make America America again.” He is scheduled to speak to voters on Thursday at a town hall-style meeting at New England College in Henniker, N.H.