Rep. Joe Sestak’s (D) anticipated 2010 Senate bid would immediately put his southeastern Pennsylvania district in play and give Republicans a shot at regaining some of the territory lost over two disastrous election cycles.

Sestak has said he intends to run against party-switching Pennsylvania Sen. Arlen Specter in the Democratic primary, provided that his family signs off on the decision in the coming weeks.

Several Pennsylvania Republicans and at least one state Democrat agreed the 7th district would be the GOP’s best pickup opportunity in the state next year if there is an open-seat race. If Sestak runs for re-election, Republicans are unlikely to mount a competitive campaign against the two-term Congressman, who has proved to be a prodigious fundraiser in a district that slightly favors Democrats.

Republicans are especially optimistic about their chances of picking up the seat if former U.S. Attorney Patrick Meehan decides to switch gears and drop out of the gubernatorial race to run for Congress instead.

Meehan, who lives in Delaware County, has not publicly expressed interest in the House seat, but it has been reported that he would consider running for it. A senior adviser on his statewide campaign, Vince Galko, said he is focused on the gubernatorial race but did not explicitly rule out Meehan running for another office.

“Pat Meehan is focused on building his exploratory committee in order to bring much needed change to Harrisburg,— Galko said. “Pat has received calls from local, state and national leaders asking him to consider the House seat. He is a serious and deliberate public servant and he is always thinking of ways to best serve his community and commonwealth.—

Businessman Steven Welch (R) has already expressed interest in running for the seat. Although Republicans agree that Meehan would be their best candidate, Welch has personal wealth — a major advantage in the district that is covered by the expensive Philadelphia media market.

A source close to former Assistant U.S. Attorney Craig Williams (R) confirmed that he is interested in running for the seat again, whether or not Sestak leaves to run for Senate. Williams received 40 percent of the vote against Sestak in 2008.

More Republicans could come out of the woodwork once Sestak officially makes his move to the Senate race, according to Pennsylvania Republican Party spokesman Mike Barley.

“Once it becomes clear that Sestak’s definitely going to run and not going to pull back, I think you’re going to see some people really going to get serious about it,— Barley said.

The Democrats’ top candidate has already announced he is preparing to run for the seat.

State Rep. Bryan Lentz (D) said Friday that he intends to run for Sestak’s seat as long as the two-term Congressman goes through with his statewide bid. Lentz filed to run for the seat in 2006, but local Democratic leaders pushed him out of the race in favor of Sestak.

“I’m going to take the next week or so and form a top-notch finance committee with the bigger political fundraisers and contributors from Delaware County and the region, and shortly thereafter file the papers,— Lentz said in a phone interview last week.

Party leaders in Washington, D.C., indicated that Lentz is their first choice to run to succeed Sestak. According to one Democratic strategist who has worked in the area, he is the only Democrat who could hold the seat.

“Bryan Lentz is the strongest candidate for that seat in the general election, and he would be a very strong primary candidate as well,— the Democratic strategist said.

State Sen. Daylin Leach said Monday he’s not interested. Leach said in a phone interview that he did not want to run for the House seat, plus he believes that Sestak will run for re-election to the House instead of Senate in 2010.

“I don’t feel a burning need to run for that right now,— Leach said. “If Joe Sestak does run for the Senate, I’ll certainly support Bryan and be grateful that I’m not having to run next year.—

But if Lentz does not run for the seat, there is no shortage of Democrats in the area that could make a bid. It’s unclear whether state Sen. Andy Dinniman (D) or businessman Richie Phillips (D) are interested in running for Sestak’s seat, but their names have both been mentioned as possible candidates for Rep. Jim Gerlach’s (R) neighboring 6th district seat.

Dinniman is not up for re-election until 2012, although Democrats warn that he would be more likely to run for Gerlach’s seat. An ally of Gov. Ed Rendell (D), Phillips would bring political connections and a great deal of personal wealth to the table if he decided to run for the seat — but he also lives outside of the district.

Former National Constitution Center President Joe Torsella (D) dropped out of the Senate race last month. According to a source close to Torsella, he has no interest in running for Sestak’s seat.

Democrats have carried the district in all three of the presidential elections this decade. President Barack Obama won 56 percent there last year.

Rep. Curt Weldon (R) represented the district for two decades before Sestak defeated him in 2006 after it was revealed that Weldon was the target of a Justice Department corruption probe. No formal charges were ever filed against him.