A cadre of influential Republicans long loyal to Arlen Specter have parted ways, politically speaking, with the party-switching Senator, a process that has accelerated since his defeat in the Pennsylvania Democratic primary.

David Urban, Specter’s chief of staff from 1997 to 2002, when Specter was still a Republican, is leading a coordinated effort to help get former GOP Rep. Pat Toomey elected to the Senate — even though Specter is backing Toomey’s Democratic foe.

Urban, a Western Pennsylvania native, has been joined by longtime members of Specter’s kitchen cabinet in building support for Toomey among moderate Republicans in the Keystone State and in Washington, D.C.

The group includes party insiders and current and former chiefs of staff to Pennsylvania GOP Members. Not all members of the group backed Specter after he switched parties in April 2009, but others, such as lobbyist Steve Hart, are close personal friends who stuck by him through the Democratic primary and actively aided his re-election bid.

“Nobody in this town is more of a Specter loyalist than me,” Urban said. “I would like to say, at least, that we’re very close. If he were in the general election, I’d be working my best to get him re-elected. But now that he’s out, I’d say Pat Toomey is the clear choice.”

The group that Urban is assembling is set to meet July 14 at the GOP’s Capitol Hill Club for its first strategy session.

Though they share deep roots in the Republican Party, the partnership between Urban and Toomey is a curious development given their history. In 2004, Toomey, a staunch conservative, gave up his suburban Philadelphia House seat to challenge Specter, a centrist, in the GOP Senate primary. Urban, a self-described moderate, helped Specter hold on for a narrow win.

The two camps and their supporters have been adversarial ever since. But Toomey and Urban were nonetheless cordial when they bumped into each other at an event in Pennsylvania before the May 18 Democratic primary, which Specter ultimately lost to Rep. Joe Sestak.

Toomey asked Urban whether he’d be willing to support him if Specter was defeated. Urban, still confident of victory and proudly wearing his “Specter, Democrat” sticker at campaign events in the state, didn’t give the idea serious consideration until the race concluded. At that point, the two reached out to each other, and after a warm phone conversation, Urban was on board.

“Most of the moderate Republicans were on board with us after the party switch. But there were a core of folks that were close to Specter for 30 years that we’re working hard to bring on board,” Toomey campaign manager Mark Harris said. “There’s a group of folks who have personal relationships with him that, as a percentage of the electorate, are insignificant, but as opinion leaders they are influential.”

Jeff Loveng, Rep. Bill Shuster’s chief of staff, described the partnership as productive for both parties, although he noted that it holds particular value for Toomey, who has been out of the D.C. loop for some time and stands to benefit from Urban’s connections, both in Pennsylvania and the nation’s capital. Loveng, a strong advocate for Specter until his party switch, said the response to Urban’s effort to drum up support for Toomey has been enthusiastic and widespread.

“It was smart on his part to make amends with Toomey, and equally smart of Toomey to work with David. It’s a win-win for both of them,” Loveng said.

Immediately following his primary defeat, Specter pledged to support Sestak in the November matchup with Toomey and even introduced his rival to the Democratic Conference at a recent caucus lunch.

Meanwhile, Republicans who had stayed with Specter after his April 2009 party switch were gravitating toward Toomey. K Street and the business community, both of which would have supported Specter because he was an incumbent, are preparing to back Toomey. The Sestak campaign predicted that the growing D.C. support for Toomey would generate a voter backlash at home.

“It is not surprising that after dedicating his career to serving the Wall Street agenda that Congressman Toomey has the backing of Republican insiders down in Washington,” Sestak campaign spokesman Joe Langdon said.

Despite a favorable political environment and recent polling that showed Toomey leading Sestak, the Republican’s ability to win in Democratic-leaning Pennsylvania depends on garnering the support of GOP moderates, not to mention independents and soft Democrats.

Urban can help.

His strengths are his deep ties to Pennsylvania’s important political players, particularly in vote-rich Philadelphia and the southeastern region of the state. Additionally, Urban is a member of Washington’s community of influential Republican moderates and pragmatists.

Urban’s group of old D.C. hands offers Toomey access to relationships that he did not have as a three-term conservative House Member or during his tenure as Club for Growth president from 2005 to 2008, where he made it his mission to purge GOP moderates from Congress. These relationships can elevate Toomey’s image among centrist Republican and independent voters and opinion drivers in Pennsylvania, while providing him access to key sources of campaign cash and strategic advice in Washington.

Urban’s goal is to aid Toomey on each of these fronts, and ex-Sen. Rick Santorum (R-Pa.) said this effort could prove crucial to the outcome of the race against Sestak.

“There were a lot of Republicans who’ve been close to Arlen for a long time, who are moderates … that were going to be problems for Pat to get, and I think all of those people are very gettable now,” said Santorum, who helped Specter beat Toomey in the 2004 GOP Senate primary by personally vouching for him in conservative circles. Santorum, ousted in 2006, is backing Toomey this time around.

“Urban’s one of those key guys; he knows all of the key players in state. He knows all of the people Toomey needs to get,” Santorum added. “Getting Urban on board was a big move for him, and I think he’ll help Pat get others to come along.”