Choosing sides in the increasingly contentious Democratic presidential contest, Sen. Bob Casey (D-Pa.) plans to endorse Sen. Barack Obama (D-Ill.), a spokeswoman for Casey confirmed on Friday morning.

The move is significant because Casey had pledged to remain neutral before Pennsylvania’s April 22 primary, the next big prize in the nomination fight.

It could also help Obama persuade working-class white voters, specifically men, to support his candidacy in a state where his primary foe, Sen. Hillary Rodham Clinton (D-N.Y.), is leading handily in the polls. Obama has lagged with those voters in contests in Ohio and Texas.

Casey, the son of a popular former Keystone State governor, appeals to Catholics because he is conservative on some social issues, opposing abortion rights and gun control.

Casey will join Obama as he kicks off a six-day tour of the state on Friday.

The move highlights what is becoming an increasingly fierce Democratic primary battle in which every endorsement counts. The endorsement fight is playing out in the halls of Congress, where Obama and Clinton are dueling for the allegiance of superdelegates to the national convention in Denver in August.

Meanwhile, Democratic National Committee Chairman Howard Dean told CBS News on Friday morning that superdelegates should make a decision on who they will support by July 1.

— Rachel Van Dongen and Erin P. Billings