WASHINGTON (AP): Barack Obama is increasingly turning his political guns on John McCain, blasting the presumptive Republican nominee's stands on the Iraq war and the economy while seeming to ignore his rival for the Democratic presidential nomination, Hillary Rodham Clinton.

In a town-hall session in northeastern Pennsylvania on Tuesday, and in other campaign appearances in recent days, Obama has sought to transform what is still a nomination fight with Clinton into a general election matchup between him and McCain.

In Philadelphia, however, Clinton was lashing both the Republicans and Obama, most notably with vows not to quit the race and comparisons of herself to the legendary film boxer Rocky Balboa from the Pennsylvania city.

Clinton has come under pressure from some Obama supporters in recent days to drop out of the contest because of what some see as the Illinois senator's insurmountable delegate lead with just 10 primaries and caucuses to go.

``Let me tell you something, when it comes to finishing a fight, Rocky and I have a lot in common. I never quit. I never give up. And neither do the American people,'' Clinton said at the Pennsylvania AFL-CIO convention. The organization is one of America's largest labor union federations.

The April 22 Pennsylvania vote, in which polls show Clinton leading Obama by double-digits, is key to the former first lady's bid to whittle down her opponent's overall lead in popular votes, delegates and states won.

According to the Associated Press tally of delegates, Obama leads Clinton 1,632-1,500, including the so-called superdelegates, elected officials and party leaders who can vote for whichever candidate they want regardless of primary and caucus outcomes. A total of 2,024 delegates are needed to win the nomination at the party's national convention this summer in Denver.

But Obama is attempting a pivot, turning his attention to McCain as if victory in the increasingly bitter nomination race against Clinton were a foregone conclusion.

``He's on a biography tour right now,'' Obama said of McCain. ``Most of us know his biography, and it's worthy of our admiration. My argument with John McCain is not with his biography, it's with his policies.''

McCain has opened a drive in recent days to define himself as a candidate with an impeccable military pedigree and experience in national security issues absent in either Clinton or Obama.

For his part, Obama has argued that a McCain victory would be another four years of President George W. Bush on economic and military policies.

``Senator McCain has been saying I don't understand national security, but he's the one who wants to keep tens of thousands of United States troops in Iraq for as long as 100 years,'' Obama said.

McCain has said the U.S. could end up having a long-term military presence in Iraq, similar to the more than 50-year presence of U.S. soldiers in Germany and South Korea.

``One hundred years in a country that had nothing to do with 9/11 may make sense to George Bush and John McCain but it is the wrong thing to do,'' Obama said, drawing applause at the town-hall session.

McCain spokesman Tucker Bounds said Obama's remarks showed his ``complete lack of preparedness to be commander in chief.''

``His attempt to paint McCain's position as something else is nothing but the disingenuous, old-style politics that he claims to reject,'' Bounds said.

Clinton assaulted McCain as a candidate who would stand back and watch as the U.S. economy spiraled downward and blamed Bush for the nation's deepening financial difficulties.

The New York senator announced plans to create 3 million new jobs to rebuild the U.S. infrastructure _ a bid to appeal to working-class voters, an important voting bloc in the Pennsylvania primary, where 158 delegates are at stake.

Clinton said her 10-year jobs-creation program _ an ``aggressive infrastructure agenda'' _ was needed because ``President Bush has stood by and watched as we've lost 3 million manufacturing jobs. And he's done nothing about the loopholes in our tax code that actually encourage companies to ship jobs overseas.''

Obama latched onto the same theme, promising to create jobs by using $60 billion (euro38.31 billion) he said would be saved by ending the Iraq war.

Race and gender, two issues that can produce heated debate in the United States, cast a long shadow over the Democratic contest this year. A November victory by either candidate would be historic _ Obama would become the first African-American president, Clinton would be the first woman.

That subtext prompted an African-American congressman who backs Clinton to say white voters are supporting Obama because he is articulate and his election would signal, true or not, that race was no longer a dominant issue.

``For white Americans, it's like, this guy can speak,'' Missouri Rep. Emanuel Cleaver told the Canadian Broadcasting Corporation. ``If you put him on a level with a lot of other African-American public speakers, he may not even measure up.''

``I think for many white Americans, they are looking at Barack Obama and saying 'This is our chance to demonstrate that we have been able to get this boogeyman called race behind us,''' said Cleaver, who predicts Obama will win the presidency.