WASHINGTON: The Democratic candidates took the heat out of what had become an increasingly bitter presidential campaign, with front-runner Barack Obama saying in their nationally televised debate that Hillary Rodham Clinton should not be judged for exaggerated remarks about her trip to Bosnia.

And Clinton, struggling to keep her campaign afloat, acknowledged that Obama could beat Republican John McCain in the November election. But she refused to let up Wednesday night on the Illinois senator's comments that small-town Americans had grown bitter over economic difficulties and were clinging to religion and guns.

Obama holds a sizable _ perhaps insurmountable _ lead in delegates with just 10 primary and caucus contests remaining after Tuesday's critical Pennsylvania vote. She needs to win by a large margin there to keep her candidacy alive.

The senators _ Clinton of New York and Obama of Illinois _ are running rough-and-tumble campaigns for the Democratic nomination and have attacked one another with increasingly personal criticism.

Clinton, apparently trying to put the Bosnia issue behind her, said she was sorry she ``said some things I knew not to be the case.''

On at least three occasions Clinton told campaign audiences that she landed in Tuzla 12 years ago under sniper fire and had to run to waiting vehicles for safety. Television pictures of the event showed Clinton walking calmly to a waiting group of people and no evidence of gun fire.

Obama said she ``deserves the right to make some errors. I've made some too.'' And he decried the tendency of modern-day politics to judge candidates according to the gaffes they make on the campaign trail.

He, too, has struggled in recent days to overcome the controversy caused by his comments about small town despondency.

Obama said he was attempting to say that because voters feel ignored by government, ``they end up being much more concerned about votes around things like guns where traditions have been passed on from generation to generation. And those are incredibly important to them.''

Clinton shot back: ``People don't cling to their traditions on hunting and guns'' out of frustration with their government. She charged that Obama had a fundamental misunderstanding on the role of religion and faith.

While both candidates said they believed either of them could defeat McCain, they declined to offer their rival the vice presidential slot.

Clinton at first sidestepped the question about Obama's ability to win, but when asked a second time, she replied, ``Yes, yes, yes.''

Obama said, ``Absolutely and I've said so before'' _ a not-so-subtle response to frequent claims by Clinton's aides that he could lead the Democrats to defeat in the fall.

On offering one another the vice presidency, Obama said he thought ``very highly of Senator Clinton's record'' but that it was ``premature at this point to talk about who the vice presidential candidates will be.''

Clinton said: ``I'm going to do everything I possibly can to make sure that one of us takes the oath of office next January. I think that has to be the overriding goal.''

Both candidates vowed again to pull U.S. troops out of Iraq. If elected, Clinton said she would immediately call together her military leadership and develop a plan to begin withdrawing forces within 60 days.

Obama said he would live up to his pledge to pull troops out within a year of taking office, realizing he would have to rely on the tactical advice of the military leadership.

On Iran, the agreed the United States should respond forcefully if it obtains nuclear weapons and uses them against Israel.

``An attack on Israel would incur massive retaliation by the United States,'' said Clinton.

Obama said, ``The U.S. would take appropriate action.'' The debate was the 21st of the campaign for the nomination, an epic struggle that could last weeks or even months longer.

Clinton's lead in Pennsylvania has narrowed, according to a new Franklin & Marshall College poll. The survey, released on Wednesday, showed Clinton with a 46-40 percentage point advantage over Obama. Her 6-point lead is just outside the poll's margin of sampling error, which is plus or minus 5.1 percent.

In March the same poll showed her ahead by 16 points, 51-35 percent. The latest poll was conducted April 8-13 among 367 likely Democratic voters.

A new Gallup Poll shows Obama with an 8 percentage-point lead nationally over Clinton, 50-42, among Democrats nationwide. More importantly, he has a solid lead in delegates who will choose the nominee at the party's convention in August. The poll was conducted April 13-15 and surveyed 1,282 Democratic and Democratic-leaning voters.

Going into the Pennsylvania primary, Clinton trails Obama 1,643-1,504. Pennsylvania is the largest state still to vote and 158 delegates are at stake.

Because Democratic state contests are not winner-take-all, it is statistically extremely unlikely for Clinton to overcome Obama's lead in the so-called pledged delegate count.

Neither candidate will be able to clinch the 2,025 delegates needed to win the nomination without the approval of the party's nearly 800 superdelegates. Of that group, 254 have said they back Clinton, and 229 are supporting Obama. His overall delegate lead includes the committed superdelegates.