Having just staked his credibility on returning a moderate colleague to the Senate, conservative Sen. Rick Santorum (R-Pa.) is finding himself in a somewhat unfamiliar spot on the political spectrum, winning slaps on the back from establishment insiders and quizzical looks from some “movement” conservatives.

Santorum, in recent years the chamber’s leading social conservative, is still reaping praise from within the Senate Republican Conference — the ideologically diverse caucus he chairs — for the assistance he gave moderate Sen. Arlen Specter (R-Pa.) in fighting off a primary challenge from the right.

Specter’s primary campaign offered the most obvious example of how Santorum has sought to put the work of the Republican Conference ahead of the ideological purity that his conservative supporters and his liberal detractors alike have come to expect.

Santorum, the third highest ranking Republican in the Senate leadership, makes no apologies for his decision to back Specter. Santorum said that once he made the decision to support his home-state colleague, there was only one way for him go about it — full throttle.

“I don’t do anything with the intent of not winning,” he said last week. “I don’t do anything to lose.” That approach, he said, will govern both his upcoming effort to re-elect President Bush as well as his bid for a third Senate term in 2006.

Santorum, who turned 46 on Monday, waves off any questions about his future ambitions, particularly the race to succeed Majority Leader Bill Frist (R-Tenn.) at the end of 2006, when Frist is expected to retire from the Senate. But Santorum’s colleagues said that his efforts to aid Specter, as well as Bush and other Senate candidates, are sure to be noted.

“That was a courageous thing to do,” said Sen. Trent Lott (R-Miss.), adding that it would help demonstrate Santorum’s commitment to the so-called “Old Bull” veterans who have tended to view him mostly as a firebrand. “He reaches across the philosophical barriers,” Lott said.

Another GOP Senator, requesting anonymity, said Santorum’s efforts demonstrated that he lived up to the “team player” concept that the Republican Conference chairman himself speaks of so frequently — namely, looking out for the best interests of a conference that had long ago agreed that Specter was a better general-election candidate than Rep. Pat Toomey (R), who ran an aggressively conservative race.

Pointing to Specter’s razor-thin 12,000-vote edge, this Senator said of Santorum: “Most importantly, he delivers.”

Santorum said his decision was prompted only by what he thought was best for his state and his own personal values. He flatly rejected claims that his support of Specter was tantamount to abandoning his conservative positions.

“I did what I think is the right thing,” Santorum said. “I don’t think there is anything I have done that is inconsistent with the causes I believe in.”

But Santorum’s comfort with his decision has not swayed all conservatives. Santorum’s actions in the Specter-Toomey race kicked off a debate among the conservative activists who have been his main base of support since he was elected in the Republican tsunami of November 1994.

On the one hand, many conservatives take the view that Santorum had no option other than to support a senior home-state incumbent who was already backed by Bush and the rest of the Senate Republican leadership.

“It doesn’t diminish him at all,” said Tom Minnery, vice president of public policy at Focus on the Family. While the founder of Minnery’s organization, James Dobson, campaigned actively for Toomey, Minnery suggested that Santorum’s reservoir of goodwill among conservatives such as Dobson “remains very deep.”

“We understand the political role that the other Senator from the same political party has to play,” Minnery said. “We don’t agree with it, but we understand. If it were an open seat, I’m sure Santorum would have followed his conscience.”

Some conservatives argue that Santorum’s efforts on behalf of Specter went well beyond a general endorsement. They accuse him of actively undermining Toomey’s conservative supporters and, in the process, putting at risk Santorum’s normally strong ties to activists.

“He made it a crusade,” said Paul Weyrich, a doyen of the right and founder of the Free Congress Foundation. “He left no stone unturned. He went out of his way to try to prevent Toomey from winning.”

Weyrich added that the concern is highest among anti-abortion rights activists who abhor Specter’s mostly pro-abortion rights positions and who have admired Santorum’s outspoken support of anti-abortion legislation.

This “backlash,” Weyrich said, grew from confrontational meetings Santorum held with leaders in the anti-abortion community prior to the primary.

Weyrich said that Santorum meant as much to Specter’s primary hopes as did Bush, who campaigned with Specter and Santorum a week before the April 27 primary. The trio also appeared in ads paid for by the National Republican Senatorial Committee.

“A lot of people told me that, more than George Bush, Rick Santorum delivered for Arlen Specter. Had he not gone the extra mile, Specter would not have won,” Weyrich said.

Specter, in an interview, almost agreed with that, calling Santorum’s aid “enormously helpful. He went above and beyond the call.”

In addition to the appearance with Bush, Santorum also cut radio and TV ads for Specter that blanketed media markets in the winter and spring. Santorum wrote a direct-mail pitch to his supporters on behalf of Specter in the winter, and he also traveled the state at Specter’s side on the last day of the primary campaign.

Despite their differences in generation, ideology and geography, Specter, a 74-year-old Philadelphian, said he and Santorum, a suburban Pittsburgh native, had developed a relationship around “three P’s: professional, political and personal.” In Santorum’s first Senate race against Harris Wofford (D) in 1994, Specter — after initially opposing Santorum’s bid — loaned him his top in-state political adviser at a low ebb in Santorum’s campaign.

Since then, the two have worked closely together — Santorum even backed Specter’s quixotic and short-lived White House bid in 1995 — and they have played off each other’s strengths and weaknesses to buttress their respective political standing statewide.

To that end, Specter said, Santorum has his vote for any future leadership race — “anything, including president.” While some see the White House as Santorum’s ultimate objective — Weyrich had previously touted him as a replacement for Vice President Cheney if health concerns were to force him out — the most immediate scenario will hit in 2006.

At that point, Santorum will have reached the end of his six-year-term limit as Conference chairman, leaving him with an up-or-out decision. With Frist expected to retire, Santorum could jump into a race for leader, which would likely put him on a collision course with Majority Whip Mitch McConnell (R-Ky.). Alternately, the Whip’s post could be Santorum’s for the taking.

However that plays out, Santorum has turned his political operation into one of the party’s strongest in Congress. He is chairing Pennsylvania for Bush-Cheney ’04 Inc., and not just in the nominal way that many Senators do in their home states. Santorum has placed top aides in charge of the Keystone State’s presidential campaign, and he’s actively talking several times a month to top political operatives such as Karl Rove and Bush-Cheney ’04 campaign manager Ken Mehlman.

In these roles, Santorum frequently analyzes precinct-by-precinct data on voting patterns. “I feel like I’m running a campaign for state representative,” he said.

In the meantime, America’s Foundation, Santorum’s leadership political action committee, has raised the fourth-largest pot of Congressional PAC money — almost $1.8 million — and among Senate Republicans, only Frist has given more money to candidates and party committees.

Santorum also continues to host what he calls “Breakfast Clubs” in Philadelphia — usually early-morning fundraisers for incumbents and challengers who can take a short Amtrak ride up and back to Washington and come away with an easy haul of money from donors.

Santorum’s supporters say that his dozen Breakfast Club events have raised $390,000 for 12 campaigns so far this cycle, with three more breakfasts on the way.

Even his current critics in the conservative wing of the GOP — including Stephen Moore, president of the Club for Growth, which pumped a few million dollars into the campaign to oust Specter — aren’t sure how long their disgruntlement will last.

“A lot of members [of the Club for Growth] say they’ll never give to him again,” Moore said. “I don’t know whether they’ll forgive or forget.”

If he can pull off his own political trifecta — Specter’s re-election, Bush winning Pennsylvania and winning re-election himself in 2006 — his future in GOP circles could be limitless.

“He would be very highly regarded,” Weyrich said.