Pennsylvania and New Jersey each will lose a seat in Congress as a result of slow population growth over the last decade.

The losses, announced Tuesday by the U.S. Census Bureau, reflect the decades-long shift of political clout from the Northeast and Midwest to faster-growing areas of the West and South.

In other words, Florida's and Texas' gain are Pennsylvania's and New Jersey's loss.

With 435 seats in the House of Representatives to be apportioned on the basis of the 2010 census, Pennsylvania's share will drop from 19 seats to 18 and New Jersey's from 13 to 12.

Texas will gain the most seats, four. It will rank second only to California, which retains 53 seats.

The Lone Star State will have twice the House delegation it had in 1920. Pennsylvania, which has lost more seats than any other big state, will have half what it had 90 years ago.

"Although it is disappointing, this result was expected," said State Senate Majority Leader Dominic Pileggi (R., Delaware). "It is one of the consequences of the fact that Pennsylvania's population growth has not kept pace with other states."

Gov. Rendell, appearing Tuesday night on CNN, said Pennsylvania's plight could have been worse. He noted that the state had lost "multiple seats" in several previous censuses.

Still the sixth-largest of the 50 states, Pennsylvania had its population grow 3.4 percent from 2000 to 2010, compared with 9.7 percent for the nation as a whole. As of April, according to the census, it had 12,702,379 residents.

New Jersey's population grew at a slightly faster rate - 4.5 percent, to 8,791,894. It slid from ninth-largest to 11th.

The population changes tallied by the census every 10 years dictate a reallotment of congressional seats. They also set the stage for state legislative districts to be remapped to account for shifts within states. That makes the count critical to both major parties' interests in Harrisburg and Trenton.

More detailed community-by-community population data are to be released by the census starting in February. But party leaders are already thinking about which members of Congress may get squeezed out by the realignment.

If the past is any guide, the remapping is likely to be highly politicized. In Pennsylvania, Republicans will be in the driver's seat.

That is because the Nov. 2 election gave Republicans control of the governorship and state House; they already ruled in the Senate. This puts them in position to redraw districts to suit their own needs.

Courts have held that districts must have equal populations. But they can be gerrymandered to favor one party.

Pennsylvania political sources say GOP leaders are likely to push two Western Pennsylvania Democrats - incumbents Jason Altmire and Mark Critz - into the same House district. The pair would then have to fight it out in a 2012 Democratic primary.

Population estimates have shown growth in some areas of the state - the Poconos and parts of the South and Southeast - while other areas, especially in Western Pennsylvania, have declined.

There is talk that the GOP may also move to protect Bucks County's Republican congressman-elect, Mike Fitzpatrick, by rejiggering district lines. Some Philadelphia voters now within the borders of his Bucks-centered district may be moved to U.S. Rep. Allyson Schwartz's district.

Schwartz, a Democrat in a district that is mostly in Montgomery County, is already in a strong position politically, so the shift would not affect the power balance.

Like most states, Pennsylvania allows party chiefs to control the remapping triggered every 10 years by the census.

"Our process is totally political," said former U.S. Rep. Joseph M. Hoeffel III, now a Montgomery County commissioner. "Other states have figured out ways to make it much less political. They have a commission. They have figured out a way to do it on a more bipartisan basis."

Hoeffel knows how these things play out. A decade ago, he was in Congress when the census dictated that Pennsylvania would lose two seats.

Republicans, also in control of Harrisburg then, combined Hoeffel's district with that of U.S. Rep. Robert Borski, a Philadelphia Democrat. It looked as if Hoeffel and Borski were headed for a primary battle in 2002 till Borski decided to retire.

New Jersey, by contrast, has a bipartisan commission handle redistricting. Twelve members, evenly divided between the parties, select a 13th who becomes chairman - and possibly the tie-breaking vote in mapping disputes.

New Jersey GOP Chairman Jay Webber, a Morris County assemblyman, said: "Taking it out of the legislative process does make it as apolitical as you can make it - which isn't very much."

Rider University political scientist Ben Dworkin said New Jersey was unique because it does not redraw districts based on which party is in power. Though Republican Christopher J. Christie is governor, Democrats control both houses in Trenton.

This system gives both parties a fair shot at maintaining some control over who gets axed, Dworkin said.

Even so, there will be blood. No House member from the Garden State has announced plans to retire, and one must go.

But go from where? Not likely South Jersey, said U.S. Rep. Robert Andrews, a Democrat who represents parts of Camden and Gloucester Counties. He points out that the main loss of population has been farther north.

"It's really a tale of two states," Andrews said. "There has been population growth in our part of the state."

It is impossible to figure out what the state's redistricting commission will do. But it is likely that, as in Pennnsylvania, two incumbents will see their districts combined and be forced to run against each other if both want to remain in Congress.

Only six other states use commissions to redraw House districts, said Tim Storey, redistricting analyst for the National Conference of State Legislatures - Hawaii, California, Washington, Idaho, Arizona, and Montana.

"Redistricting is an imperfect science, and it's political no matter how you do it," Dworkin said. "It's almost impossible not to be political, especially when you have this musical-chairs situation where someone is going to lose his seat."

Contact staff writer Tom Infield at 610-313-8205 or tinfield@phillynews.com.