Barack Obama, at the first Democratic presidential debate in nearly two months, urged voters Wednesday night to look past the gaffes and misstatements of the past few weeks, while Hillary Clinton continued to hammer him for recent controversies and raise questions about his electability.

Clinton, however, conceded that Obama can win the White House this fall, undercutting her ongoing efforts to deny him the nomination by suggesting he would lead the party to defeat.

The two candidates faced off in Philadelphia just days before the critical April 22 Pennsylvania primary. The debate came as Obama faced criticism for telling a group of San Francisco donors that small-town voters are bitter over lost jobs, and as there still are lingering questions about his relationship with his former pastor Rev. Jeremiah Wright Jr..

Both matters came up in the first few questions of the debate, which seemed to cycle through all the political mis-steps since the last debate Feb. 26.

Click here to see photos from the Philadelphia debate.

"For us to be obsessed with these kinds of errors I think is a mistake," Obama said in a general comment on campaign bloopers.

On the "bitter" remark, he said he was attempting to say that because voters feel ignored by government on economic issues, "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."

But Clinton again criticized Obama for the statements.

"People don't cling to their traditions on hunting and guns" out of frustration with their government, Clinton said. She added that Obama had a fundamental misunderstanding on the role of religion and faith.

On Wright, she reiterated that the pastor would not have been her pastor and called the issue a "legitimate area ... for people to be exploring."

A few minutes later, it was Clinton's turn to explain a mistake. Asked about her erroneous statement that she had braved sniper fire during a landing in Bosnia as first lady in 1996, Clinton issued a first-ever public apology for the error.

"I may be a lot of things but I am not dumb," she said, adding that she had written in her book that there had been no gunfire during the episode. She said she was embarrassed by her error. "I'm sorry I said it," she added.

Clinton said she's the stronger candidate in the general election because "I have a lot of baggage and everybody has rummaged through it for years," but Obama said Clinton learned the wrong lesson from her scrutiny at the hands of Republicans.

Citing the fallout over his San Francisco comments, he said: "The problem is that's the kind of politics we've been accustomed to, and I think Sen. Clinton's ... adopting the same tactics."

Asked why he doesn't usually wear an American flag pin, Obama again said that's a "manufactured issue." And asked about his association with William Ayers, former member of the violent left-wing group the Weather Underground, he said: "This kind of game in which anybody who I know, regardless of how flimsy the relationship is, that somehow their ideas could be attributed to me -- I think the American people are smarter than that."

Clinton argued the Ayers issue makes Obama vulnerable to Republicans, but Obama shot back that former President Clinton actually pardoned members of Ayers' group, making her a victim of her own "vetting standards."

After nearly a week of increasingly personal criticism, though, both candidates seemed eager to temper their rhetoric slightly.

Asked about reports that she once told New Mexico Gov. Bill Richardson that Obama couldn't win when he called to tell her he would be endorsing the Illinois senator, Clinton said that in fact he can win.

"Yes, yes, yes," she said when pressed about Obama's electability, adding that she thinks she could do a better job.

But neither candidate would pledge a spot on their ticket this fall to the loser of their epic battle for the Democratic presidential nomination.

"I think very highly of Sen. Clinton's record, but I think it is premature at this point to talk about who the vice presidential candidates will be because we're still trying to determine who the nominee will be," Obama said in the opening moments of the debate.

"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," Clinton said.

At the end of the debate, neither rival was willing to say they would ask President Bush to serve in any capacity after he leaves office. Obama volunteered he would be "more likely to ask the advice of the current president's father. He said, that as president, George H. W. Bush had presided over a "wise foreign policy" at the time the Cold War was ending.

Over the course of the two-hour face-off, both rivals pledged not to raise taxes on individuals making less than $200,000, and said they would respond forcefully if Iran obtains nuclear weapons and uses them against Israel.

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

"The U.S. would take appropriate action," Obama said.

They differed over Social Security when Obama said he favored raising payroll taxes on higher-income individuals. Clinton said she was opposed, her rival quickly cut in and countered that she had said earlier in the campaign she was open to the idea.

Under current law, workers must pay the payroll tax on their first $102,000 in wages. Obama generally has expressed support for a plan to reimpose the tax beginning at a level of $200,000 or more.

Obama erred at one point by saying he had never favored a ban on handguns even though as a state Senate candidate in 1996 he filled out a questionnaire from an Illinois voter group saying he would support such a ban.

"My writing wasn't on that particular questionnaire ... as I said, I have never favored an all-out ban on handguns," Obama said, even though his handwritten notes did appear on its front page. The response to the question about guns was typed.

Pennsylvania's primary has 158 convention delegates at stake, the largest prize remaining before the primaries end on June 3.

Obama leads Clinton in the delegate chase, 1,643-1,504. Earlier in the day, he picked up the endorsements of three superdelegates from a pair of states with primaries on May 6 -- Reps. Andre Carson of Indiana and Mel Watt and David Price of North Carolina.

The Associated Press contributed to this report.