FACTBOX: Clinton and Obama face showdown in Pennsylvania

(Reuters) - Pennsylvania holds a Democratic primary contest on Tuesday that could determine whether the party's presidential nomination goes to Illinois Sen. Barack Obama or New York Sen. Hillary Clinton.

Following are facts about the state.

* Pennsylvania has 7.2 million registered voters. Nearly 4 million are Democrats.

* The state has voted for a Democrat in presidential general elections since it backed Republican George H.W. Bush over Democrat Michael Dukakis in 1988.

* Clinton had been leading Obama by double-digit margins, but the state race has tightened. A new Quinnipiac University poll showed her lead at 7 points, down from 12 points in mid-March.

* Clinton, who lags Obama in national polls, must win Pennsylvania to remain in the race.

"If she can't win Pennsylvania, she's done. Every argument she's had is gone," said Terry Madonna of Franklin and Marshall College in Lancaster. "If Obama can cut her lead to low single-digits, he could declare victory in a state where she was expected to do better than Ohio, which she won by 10 points."

* With the electoral battle along racial, class and geographical lines, the key to victory may lie with moderate suburban Democrats in areas where newer high-tech and biomedical industries have replaced the state's traditional steel and coal economy.

Obama needs to win big in the city of Philadelphia, which has a large black population; Clinton is likely to do best in the industrial centers in the northeast and western sections of the state, home to large numbers of white, blue-collar voters and the elderly.

* Pittsburgh and the densely populated Philadelphia suburbs could help Obama with a large number of Democrats who are white, educated, affluent and liberal.

(Reporting by David Morgan; editing by David Wiessler)

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