When Sen. Arlen Specter (Pa.) announced last month that he planned to switch parties to run for re-election as a Democrat in 2010, he had the backing of Democratic Senate leaders and the full support of President Barack Obama and the White House.

But less than one month after his surprising announcement, Specter’s support from his Democratic colleagues in the Keystone State delegation is a mixed bag — with a few openly backing him but a majority choosing to keep their powder dry for now.

“I think we’re all waiting to see how Sen. Specter votes,— Rep. Patrick Murphy (D) said. “We have to make sure we pass the agenda for the American people, but we welcome him into the Democratic family.—

Some Democratic Members might be holding off on wading into the race until Rep. Joe Sestak (D) makes a decision about whether he will challenge Specter. With more than $3 million in his campaign bank account, Sestak said last week that he was still “very strongly considering getting in— the race — even if it means running against a 30-year Senator backed by Obama and the state’s two pre-eminent Democrats, Gov. Ed Rendell and Sen. Bob Casey.

Sestak, or any other Democratic candidate, would initially appear to have a tough time beating Specter in the primary, according to a new poll conducted for the Democratic Senatorial Campaign Committee and obtained by Roll Call.

Specter led Sestak 56 percent to 16 percent among self-identified Democratic primary voters in the Garin-Hart-Yang Research Group poll of 603 registered voters taken in early May — about one week after the Senator announced he was switching parties. An additional 16 percent of survey respondents were undecided.

Since Specter’s announcement, Sestak has protested his party leadership’s unequivocal support for the Senator and their anointment of him as the party’s 2010 nominee. He said he has not approached Democratic Members from Pennsylvania but that several Members have come to him to offer encouragement.

“I’ve been kind of touched by the number who have stopped by and said something while I’ve been walking and made a nice supportive comment,— Sestak said. “These are Members. There have been some Pennsylvania Members, but there have also [been] Members throughout the House.—

Sestak declined to name which Members have spoken to him, but added that he was flattered by their offering of support.

Rep. Jason Altmire (D) said he will support both Sestak and Specter until the two-term Congressman makes a decision.

“I support both of them,— Altmire said. “They’re great. Sen. Specter is someone I’ve worked with. It doesn’t matter to me what the letter by his name is. He’s somebody who’s always been even-handed, that I get along with and have always worked well.—

Altmire said he had no plans to endorse one Democrat over the other, adding that he likes both of his Pennsylvania colleagues.

“Congressman Sestak is a friend,— Altmire said. “I came in with him in 2006, and I think he would be a great Senator. And if he chooses to run, then certainly we’re going to have a problem and [we’ll] have to make a decision.—

But not everyone is choosing to sit on the sidelines or hedge their bets while Sestak mulls the race.

Specter’s most vocal supporter within the House delegation thus far appears to be Rep. Chaka Fattah (D), who represents Specter’s base in Philadelphia and wholeheartedly gave the Senator his endorsement.

“I’m enthusiastically supporting Arlen Specter for the Democratic nomination and for re-election to the Senate,— Fattah said in a phone interview Tuesday.

Fattah cited numerous examples of work he had completed for the Philadelphia area with Specter, who he said often took the lead as a Republican. He said he told Specter last week that he would do anything to help him keep his Senate seat as a Democrat.

Rep. Robert Brady (D) stopped short of endorsing Specter’s re-election bid, but he had nothing but kind words for him. Because Brady is also the chairman of the Philadelphia Democratic Party, he said in a phone interview that he must adhere to his organization’s endorsement process later this year.

“There’s no question [Specter] would be the frontrunner right now,— Brady said. “But we have a process.—

Brady said that he recently granted Specter speaking time at a fundraising dinner this month for Philadelphia Democrats and that the crowd received him “very warmly.—

“He’s not a stranger,— Brady said. “He’s from the city of Philadelphia. … We have a great relationship, and this is only making it better.—

Rep. Tim Holden (D) has also thrown his support behind Specter, according to Trish Reilly, a top aide to the Congressman.

Democrats have picked up five House seats in Pennsylvania since Specter ran for re-election in 2004 as a Republican, just one indication of the state’s ideological shift over recent election cycles. Specter barely won the 2004 Republican primary over then-Rep. Pat Toomey, but he won re-election that year by 11 points because of crossover support from Democrats.

Specter’s switch greatly improves the chances that the seat will stay in Democratic hands in 2010. Toomey’s decision to try again to knock off Specter in the primary was a deciding factor in the Senator’s decision to bolt the party. But many GOP strategists don’t believe Toomey can win the general election, and the party continues to search for another candidate.

Rep. Christopher Carney (D), who defeated a deeply flawed Republican incumbent in 2006, said he welcomed Specter to the party, but he hedged on making an official endorsement.

“We’re talking to him,— Carney said. “We have a meeting with him coming up, and we’ll see what he has to say.—

Freshman Rep. Kathy Dahlkemper (D) also said she did not plan to wade into the race.

“I haven’t gotten involved in that race at this point,— Dahlkemper said last week. “I’m busy trying to do my job here and not worrying about the politics of 2010 at this point.—

Rep. Allyson Schwartz (D), who considered running for Senate until recently, said through spokeswoman Rachel Magnuson that she welcomed Specter to the Democratic Party but declined to make an endorsement in the race for the Democratic nomination.

When asked about Specter, Rep. Paul Kanjorski’s (D) office referred to a statement from the Congressman that welcomed him to the Democratic Party following his announcement. Kanjorski said on April 28 that he hoped his relationship with Specter “will only continue to grow as he joins the Democratic Party.—

An aide for Rep. John Murtha (D) did not return a request for comment on the matter, and Rep. Mike Doyle (D) could not be reached for an interview.