COLUMBIA, S.C. - After going AWOL for seven days, Gov. Mark Sanford admitted yesterday that he had secretly flown to Argentina to visit a woman with whom he was having an affair.

Wiping away tears, he apologized to his wife and four sons, and said that he will resign as head of the Republican Governors Association.

"I've been unfaithful to my wife," Sanford, 49, told a news conference in which he ruminated aloud on God's law, moral absolutes and following one's heart. He said he had spent the past five days "crying in Argentina."

Sanford, who in recent months had been mentioned as a possible presidential candidate in 2012, ignored questions about whether he would step down as governor.

As a congressman, Sanford voted to impeach President Bill Clinton, citing the need for "moral legitimacy."

The affair is now over, Sanford said, describing the woman who lives in Argentina as a "dear, dear friend" that he has known for about eight years and been romantically involved with for about a year.

He said that he has seen the woman three times since the affair began and that his wife found out about it five months ago.

His family did not attend the news conference.

His wife, Jenny, said that two weeks ago, she asked Sanford to leave and to stop speaking with her.

Sanford said that he wants to reconcile, and his wife's statement said that her husband has earned a chance to resurrect their marriage.

"This trial separation was agreed to with the goal of ultimately strengthening our marriage," she said.

Sanford denied instructing his staff to cover up his affair, but acknowledged that he told them he thought he would be hiking on the Appalachian Trail and never corrected that impression after leaving for South America.

"I let them down by creating a fiction with regard to where I was going," Sanford said.

"I said that was the original possibility. Again, this is my fault in . . . shrouding this larger trip."

Questions about Sanford's whereabouts arose early this week.

For two days after reporters started asking questions, his office had said he had gone hiking on the trail.

Cornered at the Atlanta airport by a reporter from the State newspaper, Sanford disclosed yesterday morning that he'd gone to Argentina for seven days.

When news broke about his mysterious disappearance, Jenny Sanford said that she did not know where her husband had gone for the Father's Day weekend.

Sanford emerged yesterday afternoon at a news conference, where he mused openly of his love of hiking and how he used to guide trips along the Appalachian Trail, and, eventually, tearfully apologized to his wife, his staff and his friends, but without yet saying why he was apologizing.

"I hurt a lot of different folks," he said, occasionally choking up throughout the news conference, which lasted about 20 minutes.

With those watching still wondering what he was admitting, Sanford said: "The odyssey that we're all on in life is with regard to heart."

The State newspaper published steamy e-mails between Sanford and the unidentified woman.

One e-mail from the governor read: "I could digress and say that you have the ability to give magnificent gentle kisses, or that I love your tan lines or that I love the curve of your hips, the erotic beauty of you holding yourself (or two magnificent parts of yourself) in the faded glow of the night's light - but hey, that would be going into sexual details."

"What I did was wrong. Period," Sanford said yesterday. State Rep. Todd Rutherford, D-Columbia, called for Sanford's resignation.

"There is nothing left to save," Rutherford said. "There is no reason for him to remain as governor."

Sanford, a former three-term congressman, was elected governor in 2002. He has more than a year remaining in his second term.

Jenny Sanford, a millionaire whose family fortune comes from the Skil Corp. power-tool company, has been central to Sanford's political career.

She ran his congressional campaigns and his first race for governor. She was an almost daily fixture at senior staff meetings, and often could be seen driving a minivan away from the Statehouse in the mornings.

The two met when Sanford, who has an MBA, was trying his hand on Wall Street. She was working at a brokerage house when he entered a training program.

Sanford's announcement came a day after another prominent Republican, Sen. John Ensign, of Nevada, apologized to his GOP Senate colleagues after revealing last week that he had had an affair with a campaign staffer and that he was quitting the GOP leadership. *