Neil Goldschmidt, 63, who was elected mayor at age 32 and served one term as governor from 1987-1991, told The Oregonian about the relationship for a story in Friday editions, shortly after resigning from two chairmanships Thursday.
According to Oregon laws in 1975, sex with a girl under 16 constituted third-degree rape, but the statute of limitations expired in 1979.
Citing only health problems, Goldschmidt on Thursday relinquished his posts from the Oregon Board of Higher Education and a company that has been trying to acquire Portland General Electric. He has been diagnosed with heart arrhythmia and blocked arteries that put him at risk of a heart attack.
Following his resignations, Goldschmidt told the newspaper he came forward after learning a weekly paper was on the verge of reporting the relationship. The Willamette Week, which publishes Wednesdays, reported on its Web site that it told the governor a day earlier it was preparing a story about his affair.
In a statement to The Oregonian, Goldschmidt said he has lived with "enormous guilt and shame" in the 30 years since the nine-month affair, which started in 1975 when he was 35. He was married at the time.
Goldschmidt said he agreed to a financial settlement with the woman in 1994, "believing I was partly responsible for her difficulties coping with her life." He did not identify her; the story on the Willamette Week's Web site said she was the daughter of a Goldschmidt aide and sometimes babysat for Goldschmidt's children.
"How can such behavior be erased when the damage to others and to myself lives on?" he said. "I have sat in places of worship each year at Yom Kippur, the day of atonement in my religious tradition (Judaism), reading in silence, searching for personal peace. And I have found that the answer to that question is that it cannot be erased.
"The pain and damage that I have caused have been with me constantly. I have known all along that my private apologies and actions, deep and true though they were, would never be enough. I apologize now, publicly and completely."
Rumors of extramarital affairs were hinted at during Goldschmidt's political career, and he decided against a second term as governor after his first marriage ended.
Besides serving as governor and Portland mayor, Goldschmidt was transportation secretary for the Carter administration, an executive with Nike and an international trade consultant.