FACTBOX: Pennyslvania endorsements for Obama, Clinton

(Reuters) - Barack Obama and Hillary Clinton have been waging a battle of endorsements leading up to Tuesday's Pennsylvania primary which could be pivotal in the Democrats' presidential nomination contest.

Much of the state's Democratic Party establishment has backed Clinton, a New York senator. But Obama, an Illinois senator, also has been able to gain key political support.

Following is a list of some major political endorsements for each candidate showing how they could prove important as Pennsylvania voters head for the polls:

OBAMA ENDORSEMENTS

* U.S. Sen. Bob Casey: Son of former Gov. Robert Casey, the junior Pennsylvania senator's backing could help Obama erode Clinton support from a key segment of the Pennsylvania electorate that is Catholic, blue-collar, socially conservative and known as "Casey Democrats" because of their loyalty to Casey's late father;

* U.S. Rep. Chakah Fattah: A long-time black Democratic leader, Fattah's endorsement could help Obama galvanize black voter support in the city of Philadelphia where analysts say he will need to win by a large margin if he hopes to win the statewide contest;

* U.S. Rep. Patrick Murphy: An Iraq war veteran and Bronze Star recipient from the Philadelphia suburbs, Murphy's support could help Obama among a key bloc of white, affluent, liberal suburban Democrats in southeastern Pennsylvania and bolster the credibility of the Illinois senator's plan to withdraw U.S. troops for Iraq, if elected.

* Allentown Morning Call and Scranton Times Tribune newspapers: The backing of the two dailies could help Obama in areas with large numbers of blue-collar voters who could be expected to back Clinton in the industrial cities of the east and northeast; the Scranton newspaper also represents a community where Clinton has deep family roots;

CLINTON ENDORSEMENTS

* Gov. Edward Rendell: A powerful figure in state Democratic politics, Rendell is a former national Democratic Party chairman whose sway extends across the state and is especially strong in the Philadelphia metropolitan area where he served two-terms as a popular mayor of Pennsylvania's largest city;

* Philadelphia Mayor Michael Nutter and Pittsburgh Mayor Luke Ravenstahl: The chief executives of Pennsylvania's two major cities may help bolster Clinton at the polls with the power of the local party machinery, especially in Philadelphia where Obama is expected to do well among that city's large population of black voters; Clinton also has the endorsement of former Pittsburgh Mayor Sophie Masloff;

* 100 mayors of towns and cities across Pennsylvania: The backing of local mayors could give Clinton an edge in the more populous areas of a state with broad swaths of rural and semi-rural communities;

* 12 Pennsylvania state legislators: Democratic lawmakers from blue-collar industrial centers in the northeast and southwest, as well as the populous Philadelphia and Pittsburgh areas, provide Clinton with influential party backing in key battlegrounds across the state.

(Reporting by David Morgan in Washington, editing by Vicki Allen)

(To read more about the U.S. political campaign, visit Reuters "Tales from the Trail: 2008" online at blogs.reuters.com/trail08/)