Obama seeks to show he can "stand the heat"

PHILADELPHIA (Reuters) - Hammered by Hillary Clinton's claim he is not tough enough for the U.S. presidency, Barack Obama worked to show that he could "stand the heat" as he faced a possible defeat in Pennsylvania on Tuesday.

As Pennsylvanians cast ballots in the state's closely watched Democratic primary, Obama took in a game of basketball, something he does often on voting days to work off stress.

Then he parried questions on subjects from the White House race to the Middle East at a Pittsburgh diner before flying to Philadelphia to indulge in the city's famous cheesesteak sandwich and court voters in a neighborhood barbershop.

Pennsylvania marks the first showdown in six weeks between Obama and Clinton who are battling for the Democratic presidential nomination and the right to face presumptive Republican John McCain in the November election.

A win for Clinton would give her candidacy a lift but many analysts say it would be extremely difficult for her to catch up to the overall lead he holds in the Democratic race.

Obama and his aides have played down expectations for his chances in Pennsylvania, where Clinton leads in the polls. They have emphasized advantages for her such as her family roots in Scranton and the strong support her husband, former President Bill Clinton, has in the state.

"As I said before, it is an uphill battle," Obama, an Illinois senator, said in Pittsburgh. "Sen. Clinton had a 20-point lead to start with and we think we have closed it but we still I think have to consider ourselves the underdog."

Outside Pat's King of Steaks, a landmark cheesesteak restaurant in Philadelphia, Obama told a radio station he would eventually emerge the winner in the Democratic race.

"A win is 50 plus one. If Senator Clinton gets over 50 percent, she has won. And I don't try to pretend I enjoy getting 45 percent and that's a moral victory. We've lost the state," he said. "I do believe we're coming to the end of this process," he said.

IN THE KITCHEN

Obama may be determined to project confidence after Clinton suggested he lacked the toughness to handle the pressures of the White House.

"If you can't stand the heat, don't run for president because it's a really hot kitchen in the White House," Clinton said on the campaign trail. She also ran an ad on the theme.

Republican allies to McCain have launched a similar line of attack against Obama, portraying him as thin-skinned because of his critique of questions posed to him in a ABC News debate with Clinton, who would be the first woman president.

Obama, who would be the first black president, was asked in the debate about comments by his fiery pastor Rev. Jeremiah Wright, his relationship with a 1960s radical and his failure to wear a lapel flag pin. The Illinois senator complained the debate did not focus enough on issues like the economy.

(Editing by Doina Chiacu and David Wiessler)