By Jeff Mason

NEW YORK (Reuters) -- U.S. Vice President Joe Biden, in an emotional interview with comedian Stephen Colbert on Thursday, said he was not in a place to say he could devote his full self to running for president again.

Biden told the host of CBS' "The Late Show" that anyone running for the White House should be able to tell Americans that his or her whole heart, soul, energy, and passion were committed to the job.

"I'd be lying if I said that I knew I was there," Biden, whose son Beau died recently, said in the interview. "Nobody has a right, in my view, to seek that office unless they’re willing to give it 110 percent of who they are."

Colbert urged the vice president to run.

"I think your experience and your example of suffering and service is something that would be sorely missed in the race," said the comedian, who suffered tragedy himself as a child when his father and two of his brothers died in a plane crash.

Positive poll numbers have led the former senator, who has twice before run for president, to consider joining the race to challenge former Secretary of State Hillary Clinton for the 2016 Democratic presidential nomination.

Clinton's front-runner status has eroded because of controversy over her use of a private email server while working in the Obama administration.

But the death of Beau Biden, who had urged his father to run, has left the vice president struggling to commit to a race.

Biden recalled a recent trip to Denver where he greeted military families and broke down when someone told him he had served with his son in Iraq.

"All of a sudden I lost it," Biden said, suggesting that was not something a presidential candidate should do. "That's not, I shouldn't be saying this: You can’t do that."

Colbert set a serious tone for most of the interview, which took place during his first week hosting the show. A few glitches showed. Biden's microphone did not work at the beginning, so the taping was stopped to fix it.

The vice president, who is known for the occasional gaffe, joked he was used to having the White House shut off his mic too.

(Reporting by Jeff Mason; Editing by Sandra Maler and Peter Cooney)