WASHINGTON—Nine years ago, John Edwards had this to say about Bill Clinton and the Monica Lewinsky affair: “I think this president has shown a remarkable disrespect for his office, for the moral dimensions of leadership, for his friends, for his wife, for his precious daughter.”

On Friday, after nearly a year of denials, Edwards confessed he’d committed his own “serious error in judgment” as he was preparing to run for president, an affair in 2006 that he said he admitted to his wife but had hoped to keep from the public.

“In the course of several campaigns, I started to believe that I was special and became increasingly egocentric and narcissistic,” Edwards said in trying to explain his behavior.

Six months ago, Edwards was among 10 presidential contenders asked about marital fidelity.

“It’s fundamental to how you judge people,” Edwards told CBS News.

Edwards declared his presidential candidacy in December 2006. His wife was at his side that day and campaigned enthusiastically with him and by herself in the months that followed. She announced in March 2007 that her cancer, formerly in remission, had returned and there apparently was no cure.

She and her husband said it was important for the campaign to continue.

Edwards dropped out midway through this year’s primaries after it became apparent he could not keep up with front-runners Barack Obama and Hillary Rodham Clinton. He recently endorsed Obama and has been mentioned as a possible running mate.

He was John Kerry’s running mate in 2004 when Kerry lost to President Bush.

In his statement Friday, he said, “It is inadequate to say to the people who believed in me that I am sorry, as it is inadequate to say to the people who love me that I am sorry.

“If you want to beat me up feel free. You cannot beat me up more than I have already beaten up myself. I have been stripped bare and will now work with everything I have to help my family and others who need my help.”

In an interview for Friday night’s “Nightline” program on ABC, Edwards admitted he had had the affair with a woman who produced videos for his campaign.

Though acknowledging a sex scandal he had dismissed as “tabloid trash” only last month, Edwards denied fathering a daughter, born to the woman, and he offered to be tested to prove it. A former Edwards campaign staff member professes to be the father. The former North Carolina senator, who was the Democratic vice presidential nominee in 2004, confessed to ABC News that he had lied repeatedly about the affair with 42-year-old Rielle Hunter. Hunter’s daughter, Frances Quinn Hunter, was born on Feb. 27 this year, and no father’s name is given on the birth certificate filed in California. After the story broke Friday, Edwards released a statement that said, “In 2006, I made a serious error in judgment and conducted myself in a way that was disloyal to my family and to my core beliefs. I recognized my mistake, and I told my wife that I had a liaison with another woman, and I asked for her forgiveness. Although I was honest in every painful detail with my family, I did not tell the public.”

“I was and am ashamed of my conduct and choices,” he said. “With my family, I took responsibility for my actions in 2006, and today I take full responsibility publicly.”

The National Enquirer first reported on the affair in October 2007, in the run-up to the Democratic primaries.

“The story is false,” he told reporters then. “It’s completely untrue, ridiculous.” He professed his love for his wife, who had an incurable form of cancer, saying, “I’ve been in love with the same woman for 30-plus years and as anybody who’s been around us knows, she’s an extraordinary human being, warm, loving, beautiful, sexy and as good a person as I have ever known. So the story’s just false.” Last month, the Enquirer carried another story — the blaring headline referred to an Edwards “love child” — stating that its reporters had accosted Edwards in a Los Angeles hotel where he had met with Hunter after her child’s birth. Edwards called it “tabloid trash,” but he generally avoided reporters’ inquiries, as did his former top aides. He said in his statement Friday he had “used the fact that the story contained many falsities to deny it,” and he called that “being 99 percent honest.”