With polls showing the Pennsylvania Republican primary closing in the homestretch, National Republican Senatorial Committee Chairman George Allen (Va.) exhorted his GOP colleagues on Wednesday to pitch in and help embattled Sen. Arlen Specter.

Specter, who is locked in an ideology-driven fight with Rep. Pat Toomey (R), was campaigning in Pennsylvania and did not attend Wednesday’s GOP Conference meeting during which Allen issued the all-hands-on-deck plea.

After the luncheon, several Senate Republicans sounded cautiously optimistic that Specter will pull out a victory in the end, although all agreed the race will go down to the wire. Privately, some Republicans concede that it will be very difficult to hold the Pennsylvania seat if Specter is defeated in next Tuesday’s primary.

Allen said he is “reasonably confident” that Specter will win. But in the end, he said, “it depends on who shows up,” and he predicted that a larger turnout will benefit Specter.

“I think he’s going to win. It will be close,” Allen added. “From all indications it will be close. But all indications also are that Arlen will win. And I sure hope he does.”

Senate GOP Conference Chairman Rick Santorum (Pa.), whose support of Specter has been crucial in helping to blunt Toomey’s charges that the senior Senator is too liberal, also expressed reserved confidence in his home state colleague’s ability to win.

“This is going to be a very close race but I think Senator Specter is going to pull it out,” Santorum said. “He’s worked it hard. He’s done it in typical Arlen fashion — workman-like, leaving no stone unturned.”

Santorum said he expected the race to tighten all along, but believes that Specter’s service to the state is his ultimate trump card.

A Quinnipiac University poll released this week showed the margin separating Specter and Toomey had narrowed to just 5 percentage points. A Keystone Poll due to be released today is expected to show Specter with a 6-point lead, but still under the 50 percent mark.

A Quinnipiac survey in early April showed Specter ahead by 15 points and also indicated that Toomey had yet to unify support among his conservative base. The new poll, however, found 51 percent of the likely voters surveyed said Specter is “too liberal,” up from 43 percent in the last poll.

“I’ve been saying from day one this was going to be a race that was decided by less than a handful of points,” said Santorum, who will campaign with Specter around the state on Monday.

Senate Majority Whip Mitch McConnell (R-Ky.) campaigned for Specter in Lancaster and Berks counties on Monday, as President Bush attended a Specter rally and fundraiser in Pittsburgh.

“I think that everybody in the conference, in one way or another, has tried to help Arlen Specter — by going there or contributing or both,” McConnell said. “We think his continued service in the Senate is important.”

Senate Republican Policy Committee Chairman Jon Kyl (R-Ariz.), who is in line to become Judiciary chairman if Specter loses the primary, has contributed to Specter and went to the state to campaign on his behalf.

Kyl said he had another trip scheduled but it was pre-empted by Bush’s visit Monday.

“It’s going to be a tight race,” Kyl said. “There’s still the perception that he’s going to win, but it’s going to be a tight race.”

During Allen’s presentation to the conference, some of Specter’s colleagues appeared to be caught off guard when they learned that the Pennsylvania primary is in less than one week.

“Some of the Senators who have still not contributed to him from their leadership PACs, said they would,” Allen said. “I said, ‘Well just call them up so they know they can buy the ads, don’t wait for it to get in the mail.’”

But while some Senators readily opened their checkbooks, time constrictions appeared to make 11th hour campaign appearances on Specter’s behalf in the final weekend before the primary virtually impossible.

Senate Majority Leader Bill Frist (R-Tenn.), for example, said his schedule was so tight over the next week that he didn’t think he would be able to parachute into Pennsylvania.

Frist’s largest fund-raising event of the year is this weekend in Nashville, for donors to his Volunteer PAC, an event from which Specter was a major beneficiary last year. In addition to receiving $10,000 from Frist’s VOLPAC, Specter took in $100,000 in bundled donations last year from the biggest contributors to the leader’s political action committee.

Specter has spent upwards of $10 million on the primary so far. Toomey, meanwhile, has spent more than $3 million.

Toomey has benefited greatly from bundled contributions from the conservative Club for Growth, which has made Specter its number one target so far this cycle.

The group estimates it has helped funnel between $925,000 to $1.1 million to Toomey’s campaign, and it has also spent $1.4 million on ads attacking Specter.

The group’s latest ad, funded through its PAC, hits Specter for going on taxpayer-funded luxury junkets around the world. The second installment of the $400,000 ad buy is expected to begin running Friday.

Allen said independent groups have the freedom to run any advertising they want, but he lamented, “It’d be nice if such a group would run positive ads.”

Sen. Susan Collins (R-Maine), one of a handful of moderates in the chamber, called Specter an “exceptional Senator” and expressed her disappointment with the efforts to defeat him.

“I think it’s destructive, the Club for Growth to go after Republicans, and it jeopardizes our ability to retain the seat,” Collins said.

Democrats’ hopes of winning in November largely hinge on Specter’s defeat in the primary. The winner of the primary will face Rep. Joe Hoeffel (D-Pa.), who has the same southeastern Pennsylvania base of support as Specter.

Specter has also argued that his presence on the ballot would help Bush win the key battleground state. Allen said Bush’s visit this week was a big boost for Specter, even as his opponents sought to frame the visit as a last-minute sign of desperation with Toomey surging in the polls.

Specter’s foes were also heartened by word that a citizens’ group is requesting that the Justice Department investigate allegations that Specter made federal aid for a transportation project in Pennsylvania contingent on his gaining support from the local GOP officials.

“I think we’ve got some momentum here at the end,” said Jon Lerner, a Toomey campaign consultant. “I think there’s much more energy among our voters then there is among his.”

Lerner predicted that Specter will get “exceedingly little of the undecideds” still left.

With little other activity on the ballot in the state next week, turnout in the primary is expected to be extremely low.

However, Specter could be boosted by a competitive GOP primary in Hoeffel’s current 13th district, an urban/suburban Philadelphia district that includes portions of Specter’s Montgomery County base.

With negative ads from both candidates flooding the state’s airwaves, one Specter supporter said the Senator’s campaign is also prepared to battle Toomey on the ground.

“You’d much rather be where Arlen is than Pat is,” said Bob Holste, chief of staff to Rep. Phil English (R-Pa.). “But you’ve got to do the turnout and that’s what everything is focused on now. It’s really a turnout game.”

English, a vocal Specter backer, recently taped a video endorsement for the Senator that will run in his western Pennsylvania district.

“You have to make sure that you have a ground game, not just an air war and they’ve got that ready,” Holste said. “It’s all in the execution now.”

Paul Kane and Mark Preston contributed to this report.