Pennsylvania Republicans on Tuesday released a surprisingly strong proposed congressional map, on which the GOP could expand on its current advantage in the state’s delegation.

With the GOP controlling 12 of 19 districts in a nominally blue state, and the state losing a seat thanks to population shifts, it was assumed that the GOP would focus its power over redistricting on shoring up its current 12 members and likely not be able to add new opportunities. That likelihood was reinforced by the party’s overreach when it drew the map in 2001 and stretched itself too thin.

But along with shoring up several vulnerable members — most to a significant degree — the GOP was able to create a very winnable district in western Pennsylvania, where the winner of a primary between Democratic Reps. Jason Altmire and Mark Critz will face another battle in the general election.

At the same time, Pennsylvania Republicans will have to defend their 2010 gains for years to come, as Philadelphia-area GOP Reps.Pat Meehan, Jim Gerlach, Charlie Dent and and Mike Fitzpatrick continue to represent swing districts.

The map is expected to pass in the state legislature as soon as this week, with little reason to believe it will be altered. Republicans control the state legislature and the governor’s mansion.

The most important part of the map for the GOP is those Philadelphia-area districts, which while in GOP hands, currently lean Democratic.

In the end, Meehan, Gerlach and Dent all got districts that are between 3 and 5 percent more Republican, according to numbers obtained by The Fix, while Fitzpatrick gained less than a point. All of them remain districts that went for President Bush in 2004 and President Obama in 2008 — showcasing their swing nature.

Fitzpatrick’s Buck’s County-based 8th district could be the hardest to hold in the years to come. Republicans got (ahem) creative in drawing the other three districts, mining Republicans from neighboring districts held by Reps. Tim Holden (D), Allyson Schwartz (D) and Joe Pitts (R) (Meehan’s new 7th district, in particular, is a sight to see and may soon be the subject of a Fix “Name that district” contest), but because Fitzpatrick’s 8th had to retain all of Bucks County, there was as much wiggle room.

The GOP also used Holden to shore up its members in the Northeastern part of the state. Holden took Democratic-leaning Scranton and Wilkes-Barre from freshman Rep. Lou Barletta’s (R) Democratic-leaning 11th district, making both men relatively safe for years to come. Barletta and fellow freshman Rep. Tom Marino (R) both saw their districts stretched into central Pennsylvania in order to get safer. (Marino already had a very Republican district, but it had been held by a Democrat previously.)

Similarly, in Northwestern Pennsylvania, freshman Rep. Mike Kelly (R) got a little help with his 3rd district picking up some more conservative areas close to Pittsburgh. His district got about 2 percent better and is now a district that would have gone about 52 percent for Sen. John McCain (R-Ariz.) in the 2008 presidential race — safer, if not completely safe.

The most surprising part of the map, though, is south of Kelly’s district in the Pittsburgh area, where Critz and Altmire were combined into a new 12th district that stretches from the western border of the state to Johnstown and went about 54 percent for McCain. That’s a better district for the GOP than had been anticipated.

There is a little caveat here, though: Both Critz and Altmire have won in conservative districts in the past, and the region they come from, while conservative, has shown a willingness to vote Democratic. In fact, Altmire’s current district is a 55 percent McCain district.

So while most districts with those presidential numbers would be consider solid GOP districts, this will be somewhat closer to a swing district in the years to come.

(Perhaps more illustrative, both Altmire and Critz have said they like the new district just fine. That may be because they know they can’t do anything to change it, but it still stays something that they aren’t screaming bloody murder right now.)

In the end, while the GOP has drawn a strong map and set itself up to keep a majority of the state’s congressional seats for years to come, it will still have to fight for them. That fight just became quite a bit easier, but it is still a fight, as four or five of the state’s seats will be among the most competitive in the nation for years to come.