As rumors flew that Pennsylvania Treasurer Bob Casey Jr. (D) is poised to challenge Sen. Rick Santorum (R) next year, former Treasurer Barbara Hafer (D) threw her hat into the Senate race Wednesday, complicating Democratic leaders’ efforts to clear the field for their preferred candidate.

Casey is considered Democrats’ top prospect to take on Santorum, the Republican Conference chairman, and if he does enter the race it would hand Senate Democrats their first big recruiting coup of the cycle.

Santorum tops the list of Democratic targets in 2006, and recent polling has shown Casey beating the two-term Senator in a hypothetical matchup.

Late yesterday, as a report on the Web site PoliticsPA.com that Casey was on the verge of entering the race circulated on Capitol Hill and back in the state, Democrats insisted that Casey is still mulling his options.

“He has not yet made a decision,” said Casey spokeswoman Karen Walsh. “We expect one very shortly.”

Hafer, meanwhile, said she is entering the race against Santorum regardless of what Casey ultimately decides.

“We’re in the race,” Hafer said in an interview, adding that EMILY’s List is helping her prepare for the contest. “We’re moving forward to develop fundraising lists and get a campaign together. So we’re in it.”

The abortion debate has already played a prominent role in discussion of the Pennsylvania race and, if both Hafer and Casey run, the issue is sure to factor prominently in the Democratic primary. Abortion-rights advocates have expressed their displeasure at the appearance that Senate Democrats are lining up behind Casey, who was on Capitol Hill in February meeting with Senate Minority Leader Harry Reid (D-Nev.) and Democratic Senatorial Campaign Committee Chairman Charles Schumer (N.Y.).

Hafer, a Republican-turned-Democrat who has run statewide five times before, favors abortion rights. Casey, like his father, the late Gov. Bob Casey (D), opposes abortion rights.

In making the case for her candidacy, Hafer argued that she would provide the starkest contrast to Santorum — fueling her ability to energize the Democratic base, including women voters.

“I think Casey and Santorum are so similar that it’s going to be very difficult,” she said. “My candidacy is a complete contrast. There probably isn’t anything that Rick Santorum and I agree upon. So I think it’s a very strong candidacy of great contrast.”

Hafer released a poll last week that showed her tied with Santorum at 44 percent in a head- to-head matchup. The same poll, however, showed Casey beating the incumbent, 47 percent to 40 percent.

Casey has privately indicated that he would be less inclined to run if he faced a competitive primary.

Other Democrats who have also been considering challenging Santorum, such as former Rep. Joe Hoeffel (D-Pa.), are considered unlikely to run if Casey does.

One Pennsylvania Democratic operative predicted that ultimately the party will avert a bruising primary and reach consensus on which candidate would be strongest against Santorum.

“I would think in the end they clear the field one way or the other,” the consultant said. “There’s a little cat and mouse [game] going.”

Gov. Ed Rendell (D) has reportedly also taken part in efforts to clear the field for Casey, his former rival. Casey lost badly to Rendell in a biter 2002 gubernatorial primary, 16 years after Rendell, who was then Philadelphia’s district attorney, was defeated in a primary by Casey’s father.

On Friday, Senate Democratic leaders will join Rendell in Philadelphia for a Social Security rally. Casey is not expected to attend the event.

Casey, who served as state auditor general from 1997 until January of this year, has always been viewed as having stronger gubernatorial ambitions than a desire to come to Washington, D.C.

David Stone, a Democratic media consultant in Pennsylvania and a former communications director to Gov. Casey and former Sen. Harris Wofford (D-Pa.), called Casey’s serious consideration of the Senate race “a truly organic movement.”

Stone said that while he couldn’t speak for Casey, “he has taken a very close look at this and decided that he’s going to answer the call and will do so, like with everything else he does, with enthusiasm and intensity.”

Casey would not be the first anti-abortion rights candidate to challenge Santorum.

In 2000, Democrats nominated then-Rep. Ron Klink against Santorum. But Klink had trouble raising money and generating excitement for his campaign and he ultimately lost to Santorum, 52 percent to 46 percent.

John Brabender, a consultant to Santorum, argued that Pennsylvania voters still know very little about Casey and that in a federal race, unlike his other statewide contests, Casey will be forced to take controversial positions.

“He’s going to have to go on record very quickly on some key issues,” Brabender said.

Meanwhile, he said Santorum is forging ahead with his re-election efforts, with little regard to who his eventual opponent may be.

“I think that any incumbent race, first and foremost, is somewhat of a referendum on the incumbent,” Brabender said. “So you can expect from the Santorum campaign an awful lot of talk about what Rick Santorum has accomplished for Pennsylvania and be more focused on that and probably less focused on Bobby Casey.”

But Brabender predicted that a potentially divisive primary could significantly affect the outcome of the general election.

“Assuming Bobby Casey wins the Democratic primary, I think the question will become again is he going to run the type of divisive campaign he ran for governor and do Pennsylvanians have the stomach for that,” he said. “Obviously they didn’t when he ran four years ago.”