WRAPUP 5-Obama defends 'bitter' remarks; McCain attacks

(Adds Clinton television advertisement, paragraph 4)

By Caren Bohan

PITTSBURGH, April 14 (Reuters) - U.S. Democratic presidential candidate Barack Obama spent a fourth day on Monday defending himself for calling people in small towns with economic blight "bitter" in a controversy that rival Hillary Clinton is trying to use for a comeback.

Republican John McCain sought political gain from the flap, saying it is the people from small towns in America who survived the Great Depression, fought in World War Two and built a strong postwar economy who are the "heart and soul of this country."

Clinton, who is vying with Obama to face McCain in the November presidential election, also pounced on Obama's remarks in an effort to revive her struggling bid to overtake Obama's lead in the state-by-state contest for the Democratic nomination.

Clinton launched a television ad in Pennsylvania featuring an announcer summarizing Obama's comments and five of her supporters in the state condemning them. "I was very insulted by Barack Obama," a woman says in the ad. "Hillary does understand the citizens of Pennsylvania better."

With tests looming in Pennsylvania on April 22 and Indiana and North Carolina on May 6, Obama was forced to spend another day explaining comments he made at a private fundraiser last week, in which the Illinois senator said economic problems had led voters in some small towns to become "bitter" and "cling to guns or religion."

"Now it may be that I chose my words badly. It wasn't the first time and it won't be the last. But when I hear my opponents, both of whom have spent decades in Washington, saying I'm out of touch, it's time to cut through their rhetoric and look at the reality," Obama told steelworkers in Pittsburgh.

Speaking to the Associated Press' annual meeting in Washington, he said many Americans are bitter about Washington not addressing economic dislocations caused by globalization, as well as high health care bills and other woes.