FACTBOX: Clinton and Obama navigate religion in Pennsylvania

(Reuters) - Religious affiliations among voters could play a vital role in the outcome of Pennsylvania's crucial April 22 presidential primary showdown between Democrats Hillary Clinton and Barack Obama.

Clinton, a New York senator, is expected to poll strongly among blue-collar Catholic voters known as "Casey Democrats" for their loyalty to the late Democratic Gov. Robert Casey.

But Obama has also attracted support from that group, with the help of an endorsement from Casey's son, Sen. Bob Casey of Pennsylvania.

Below is a breakdown of religious affiliation in Pennsylvania from the 2008 U.S. Religious Landscape Survey conducted by Washington-based Pew Forum on Religion & Public Life.

Pew surveyed 1,896 Pennsylvania adults as part of its nationwide survey and produce data for the following breakdown on religious affiliation. The survey has a 2.5 percent margin of error for Pennsylvania:

* CATHOLIC...29 PCT

* PROTESTANT MAINLINE.......25 PCT

* PROTESTANT EVANGELICAL....18 PCT

* PROTESTANT HISTORICALLY BLACK.............7 PCT