It’s crunch time in Pennsylvania.

Just four weeks before the filing deadline in the presidential battleground state, Republicans and Democrats are scrambling to fill gaps in key Congressional races.

Democrats have tried to knock off Republican Members in four suburban Philadelphia districts for a couple of cycles in a row, and they succeeded in 2006 at putting Reps. Joe Sestak and Patrick Murphy in office. But they’d like to try again in the two other districts, even though they don’t have strong contenders now.

All four southeastern Pennsylvania districts voted for Sen. John Kerry (D-Mass.) in 2004 and Al Gore in 2000, albeit by very small margins.

Meanwhile, Republicans are looking to take back the seats now held by the two freshman Democrats. Marine Reserve Officer Tom Manion (R) — whom local pols consider an A-list candidate — announced Tuesday that he was running for Murphy’s 8th district seat.

Neil Oxman, a national Democratic consultant who does work for Sestak, said Manion is the Republicans’ best chance to pick up a seat in the state. He said recruiting Manion “says they’re really going to raise real money for the guy and they’re going to have a real horse race.”

“They’re going to play there for real,” he added.

Mark Campbell, a national Republican consultant who counts Rep. Jim Gerlach (R-Pa.) as a client, said he thought Manion had a better change of winning than former Rep. Mike Fitzpatrick (R), whom Murphy defeated by about 1,500 votes in 2006. Fitzpatrick did not publicly rule out a rematch until late last year.

“Republican chances in that seat are very, very good,” Campbell said. “Manion is a top-tier candidate that folks have been talking about for a while; it just took Fitzpatrick a while to say he’s not running. Quite frankly, I think Manion has a better chance of winning as a fresh face.”

However, Republicans have so far come up short in their search for a candidate just west of Philadelphia in the 7th district seat currently held by Sestak, who had banked $1.4 million in cash on hand at the end of September.

Oxman said the National Republican Congressional Committee likely will have to put up a “sacrificial lamb” against his client.

“No matter what they say, the guy against Sestak is auditioning to run for another office,” Oxman said. “I’d be shocked if he raises much more than a half a million dollars.”

But despite their 2006 success in the region, Gerlach’s exurban Philadelphia district and Rep. Charlie Dent’s (R) seat in the Lehigh Valley remain elusive for Democrats. So far, Allentown Democratic Chairwoman Sam Bennett is running, but her paltry fundraising — only about $91,000 through the end of September — raised eyebrows.

Pennsylvania Democratic political consultant Mark Nevins said that while Dent’s district has “traditionally been less” competitive than Gerlach’s, a top-tier candidate like Lehigh County Executive Don Cunningham (D) would be “formidable” if he ran.

In the 6th district, no candidates have filed yet with the Federal Election Commission to run for the seat, though activist and former businessman Bob Roggio (D) recently announced a bid against Gerlach.

Attorney and businessman Richard Phillips Jr. (D) said he has been approached by Gov. Ed Rendell (D) and other local officials about running for the Gerlach seat. In an e-mail, Phillips added that Rendell has offered his support if he decides to run.

Democrats have aggressively courted candidates for the 6th district this cycle, reportedly including former “West Wing” actress Melissa Fitzgerald and Philadelphia Magazine Editor Larry Platt, both of whom are in good company in declining to run for the seat.

Meanwhile, Democrats also are looking to expand their playing field in the 3rd and 18th districts, seats held by seven-term Rep. Phil English (R) and three-term Rep. Tim Murphy (R).

Campbell pointed to English’s valuable spot on the Ways and Means committee, plus his history in the district, as proof that the Congressman is entrenched — despite having close elections sometimes.

“Phil English might only win by 2 or 3 points, but he’s going to win by 2 or 3 points every time,” he added.

Republicans are having a similar problem in the 10th district, an area that leans decidedly Republican but where freshman Rep. Christopher Carney (D) won last year after longtime Rep. Don Sherwood was embroiled in a personal scandal. The two Republican frontrunners for the nomination, Dan Meuser and Chris Hackett, are both wealthy business owners who are running in a field of less well-known candidates.

“The big danger there is that two rich guys will blow each other’s brains out,” Campbell said.

The only open-seat race in the state could possibly add to Republican woes.

Rep. John Peterson’s (R) retirement announcement in early January left only a few weeks for candidates to decide whether to run for his now-open seat. After leading candidate and heir-apparent state Sen. Jake Corman (R) declined to run last week in favor of spending more time with his family, the field was left wide open.

According to Republican sources and local news reports, former Centre County Commissioner Chris Exarchos, hotel developer Matt Shaner and financial consultant Derek Walker are very close to announcing their bids for the Republican nomination.

One local Republican said Walker is the likely frontrunner out of those three, given he has enough funds to scare other candidates out of the race and does not carry some of the personal or political baggage that the other candidates have.

For the Democrats, 2006 Democratic nominee Don Hilliard is reportedly running again, joined by Lock Haven Mayor Rick Vilello Jr. and Iraq War veteran and former Washington newspaper correspondent Bill Cahir. However, the seat is a Republican stronghold and one of the most rural districts in the state, making it a long shot for Democratic hopefuls.

“It’s important to separate [Democratic Congressional Campaign Committee] rhetoric from what they’re actually going to do,” Campbell said. “I think they will sucker someone into running and not give them any resources, because it’s a really bad bet.”

But political consultants on both sides of the aisle point out that if candidates do not have a serious primary race, they have plenty of time to raise the money necessary to wage a competitive general election bid.

“I think it’s hard to say right now that there’s a missed opportunity,” Nevins said. “Because I think that there are some districts where there are people percolating that haven’t officially declared because they’re kind of waiting to file for the deadline, but they’re not in a rush to do so.”