PoliticsPA is has begun ranking the most vulnerable U.S. House seats in Pennsylvania.

In the battle for the U.S. House in 2010, there may be no state as decisive as Pennsylvania.

According to the House race ratings by handicapper Charlie Cook, 10 out of Pennsylvania’s 19 House districts are in play this fall. That’s more seats than any other state, and more than any other big state on a percentage basis.

In addition, of those 10 seats, Cook considers seven “toss-up,” “lean Democratic” or “lean Republican” – the most competitive categories. That’s also the most of any single state, both on an absolute and a percentage basis.

This is why we’re starting a new feature at PoliticsPA: a monthly ranking of the most vulnerable U.S. House seats in Pennsylvania.

In our rankings, the seats are numbered in descending order by the likelihood of a party switch.

We’re kicking off the rankings this month with 11 lawmakers; we’re considering the other eight seats safe, though that could change if circumstances shift.

The Democrats have the most at risk. Of the 11 seats we’re focusing on, seven are currently held by Democrats and another one is the vacant seat previously occupied by the late Rep. John Murtha (D). And with the national climate leaning against the Democrats, at least for now, the Keystone State could prove pivotal, as it has in several recent election cycles.

“Once again, Pennsylvania is one of the hot spots for congressional races,” said Nathan Gonzales, who handicaps races for the Rothenberg Political Report. “It’s very difficult to see Republicans getting back to the majority without doing very well in Pennsylvania.”

One caveat: It’s still early for Congressional races, and the outcomes of the May 18 primary could dramatically alter the contours of each contest listed here. These rankings give a general idea of where each race stands, but they are subject to significant change through the year.

PoliticsPA has ranked the 10th District of Pennsylvania, currently held by Chris Carney (D), as the fifth most likely to switch parties in November.

Carney won his northeastern Pennsylvania district seat in 2006 by ousting scandal-tarred incumbent Don Sherwood (R). The district went for McCain over Obama by nine points, and three Republicans have lined up to challenge Carney — former U.S. Attorney Tom Marino (an early primary frontrunner), businessman Dave Madeira and Snyder County Commissioner Malcolm Derk. But Carney has helped himself – he’s cultivated a middle-of-the-House voting record, including bucking his party on a key cap-and-trade vote earlier this year, and his continuing service as a commander in the Naval Reserve bolsters his bona fides in the district. He apparently was even bipartisan enough that House GOP leaders, with McCain’s help, courted him to switch parties late last year. The key question is whether voters will look past his party affiliation in what’s looking ever more like a wave election.

For the full list and article please visit PoliticsPA.