WASHINGTON -- In the years they have served together, Sen. Arlen Specter, one of the Senate's leading moderates, and Sen. Rick Santorum, one of the body's leading conservatives, have found themselves on the opposite sides of a number of substantive issues.

	Stem cell bill Sen. Arlen Specter, R-Pa., is sponsoring The Stem Cell Research Enhancement Act of 2005, which is also known as Senate Bill 471. It's companion in the House is House Bill 810. Here are some key facts about the legislation: Senate co-sponsors: Sen. Orrin Hatch, R-Utah; Sen. Gordon Smith, R-Oregon; Sen. Tom Harkin, D-Iowa; Sen. Dianne Feinstein, D-Calif. House sponsors: Diana DeGette, D- Colo., and Michael N. Castle, R-Del. What it would do: In 2001, President Bush announced that federal funding would be available for research on only 60 existing embryonic stem cell lines, but scientists have been able to work on only 22. Specter's legislation would allow the federal government to conduct research on frozen embryos donated from in vitro fertilization clinics that would otherwise be discarded. Couples would have to give their permission to donate embryos no longer needed for their fertility treatments. Status: The House last week passed Bill 810 by a vote of 238-194. Senate Republican leaders are deciding whether to bring the Senate version up for a vote after the Memorial week recess. President Bush has said he will veto the legislation. To overturn the veto, two-thirds of each chamber's members would have to support the legislation. 2006 Senate race: Both Sen. Rick Santorum and his Democratic challenger, Pennsylvania State Treasurer Robert P. Casey Jr., oppose Specter's legislation. But Santorum is not in favor of federal funding for any research on embryonic stem cells. Casey supports the federal guidelines issued in 2001 that provide federal funding for research on existing embryonic stem cell lines. For more information on the legislation: thomas.loc.gov/

But this year, as the thorny issue of federal financing for embryonic stem cell research winds its way back to the forefront in Congress, Pennsylvania's two senators are again sliding into the role of legislative adversaries -- this time on an issue of intense personal importance to both of them.

Specter has reintroduced legislation with a formidable bipartisan group of colleagues that would expand government funding for embryonic stem cell research far beyond the narrow limits that President Bush set in 2001. The bill would allow federal money to be spent for research on frozen embryos created through fertility treatments at in vitro clinics, as long as the embryos were going to be discarded and the couple agreed to donate them.

For five years Specter's initiative on stem cell research has languished in Congress. But his effort gained new momentum this past week when the Republican-dominated House passed an identical measure, the Stem Cell Research Enhancement Act, with a 44-vote margin -- a feat that seemed virtually impossible several years ago.

The path ahead for the legislation remains rocky. The Senate's Republican leaders, including Santorum as No. 3 in the hierarchy, are still debating whether they will bring Specter's bill to the Senate floor for a vote. Even if they do, the legislation's supporters worry that it could become a vehicle for a host of anti- abortion amendments that one senior Democratic aide described as a "legislative nightmare."

The larger hurdle is Bush's threat to veto the legislation which he considers to have crossed "a critical ethical line."

On Wednesday, Specter said he believed he could build a coalition of Senators large enough to overcome to override a presidential veto; to do that Specter and his colleagues must line up the support of two-thirds of the members of both the Senate and the House.

One of Specter's chief combatants in that effort is sure to be Santorum, the Senate's third-ranking Republican, who as Republican Conference Chairman helps shape the message and communication strategy of his party.

The two senators have a close working relationship on many issues, especially when it comes to bringing federal money to Pennsylvania but they are miles apart on stem cell research.

Santorum said in an interview that the legislation Specter has proposed amounts to "the wholesale destruction of human life paid for by the federal government."

He went on to say "We're certainly have a fight about this [in Congress]," and flatly predicted "The bill is not going to become law."

"The president is going to veto it; the House is will sustain [the veto]. So do we want to spend weeks or days or long time in a very tight Senate agenda to deal with a bill that is never going to become law? I would say no."

There is little, if any, middle ground between Santorum and Specter in their ideological arguments in the embryonic stem cell debate.

Some anti-abortion rights lawmakers, including Specter's Republican co-sponsors Utah Sen. Orrin Hatch and Oregon Sen. Gordon Smith, support embryonic stem cell research because they believe life begins when an embryo is implanted in a woman's womb.

But Santorum believes that life begins at conception -- when a woman's egg is fertilized and becomes a unique organism. Santorum takes a harder line than Bush and opposed the president's decision in 2001 to he allow federal funding for embryonic stem cell research on what was then believed to be more than 60 existing embryonic stem cell lines.

"Science is not an ethics free zone. Just because you can't do something that doesn't mean you should," Santorum said.

To expand even further beyond the president's 2001 guidelines with Specter's legislation, he said, would be unconscionable.

"You want to talk about the promoting of the culture of death -- now we're going to wholesale kill hundreds maybe thousands of human embryos for no other reason than to simply do research on their cells?" he said. "I think that's a radical step for a culture that says that we respect the human dignity of every person."

Santorum's viewpoint is unlikely to become an issue his race for re-election in 2006. His Democratic challenger, Robert P. Casey Jr. said this week that he would also oppose Specter's legislation. Unlike Santorum, Casey does support the current federal guidelines on embryonic stem cell research but he does not support expanding them.

Specter has countered Santorum's objections by pointing out that his legislation would only affect only a small percentage of the estimated 400,000 frozen embryos in in vitro clinics that would otherwise be discarded because they are no longer needed.

"When the argument is made that we should not use federal funding to save lives by destroying lives, it is simply factually incorrect," Specter said this week. "Embryonic stem cells will be destroyed whether they are used to save lives or not."

He also dismissed the argument that some taxpayers will oppose using their money for research they believe is unethical.

"Taxpayers, by our taxing system, are compelled to fund many items that they don't like," Specter said. "A lot of people didn't want to go to war in Iraq. ...And the purpose of the Congress is to make a public policy determination as to what is in the public interest."

As the chairman of Senate Appropriations subcommittee on Labor, Health and Education who helped engineer the doubling of the medical research budget for NIH between 1998 and 2003, Specter was among the earliest lawmakers to plunge into the stem cell debate.

In November of 1998, Specter was fascinated by the announcements by several teams of scientists in November of 1998 that they had who been able to isolate stem cells from human embryos and that those cells had the potential to grow into any form of tissue -- which could cure patients with even the most disabling diseases.

He called the researchers to Washington for a hearing just a month later; that led to a series of hearings in which the committee explored the science, the ethical objections and even brought in the star power of celebrities like Michael J. Fox, who has Parkinson's disease, and Christopher Reeves, who was paralyzed by a spinal cord injury, to put a human face on the stem cell debate.

In January of 2000, Specter introduced legislation with his co-chairman on the subcommittee, Iowa Democrat Sen.Tom Harkin, that would permit the government to finance embryonic stem cell research as long as the cells were derived from embryos that would have otherwise been discarded at in vitro fertilization clinics. On the Senate floor, he urged colleagues to move quickly to "give thousands of individuals a chance to see a cure within their lifetime."

Specter, and like-minded lawmakers, had welcomed Bush's 2001 pronouncement as a first step but when the number of stem cell lines that actually materialized dwindled from more than 60 to what is now 22, again began pushing to relax the ban on government financing for research on human embryos, which lawmakers had attached to spending bills since the mid-1990s.

They convinced 58 senators to sign a letter to Bush on June 2004 asking him to relax the guidelines.

When he reintroduced his legislation this year, Specter said "the time has come to really mount a major effort," and the victory in the House has given new force to that effort.

Specter, who often makes self-deprecating jokes about the fact that he has lost his hair, has said his ongoing struggle with late-stage Hodgkin's disease, a form of cancer, has given him new empathy for the struggles of patients with other diseases like Alzheimer's and Parkinson's and that barring them from getting medical care that might become available through embryonic stem cell research is "simply atrocious."

Both Santorum and Specter said this past week that they learned long ago how to disagree amicably and that the stem cell debate was not likely to alter their working relationship.

Specter, who has already held three fundraisers for Santorum's re-election bid, noted that despite their differences he had helped his junior senator raise $200,000 just this past week at a Washington fundraiser.

Last year, Santorum helped Specter fend off a well-funded primary challenge from Rep. Pat Toomey and then helped him win the chairmanship of the Judiciary Committee in the face of conservative critics who questioned whether he would vigorously support the president's judicial nominees.

"We've been on opposite sides of the fence," Specter said.

But, he said, "I'm campaigning for him in Pennsylvania.

His re-election is very important to me."