Under intense pressure from his Democratic colleagues, Rep. David Wu of Oregon said Tuesday that he would resign from Congress after accusations that he had an inappropriate sexual encounter with a young woman last year.

Wu, a seven-term member of Congress, has not publicly discussed the allegations by the woman, who was 18 at the time, although he has said their encounter was consensual. But the episode is only the most recent part of a public unraveling over the last year in which Wu, 56, had acknowledged mental-health issues and erratic behavior.

Even before the latest allegations were reported Friday by The Oregonian newspaper of Portland, Wu was considered so politically vulnerable that two fellow Democrats already had announced plans to challenge him in next year's primary. His district, which stretches from Portland to the Pacific Ocean and is home to many high-tech workers, has been in Democratic hands for more than three decades and is likely to stay that way.

The Oregonian reported that over Thanksgiving, while he was visiting a high-school friend and political donor in Orange County, Calif., Wu went outside with the friend's daughter and some sort of sexual encounter occurred.

A few months later, the newspaper said, the young woman called Wu's office and left a distraught message on the main phone line, saying Wu had forced himself on her. She did not report the encounter to the police. After the newspaper reported that phone message, Wu's aides confronted him; he acknowledged a sexual encounter, according to The Oregonian, but said it had been consensual.

The newspaper has not published the young woman's name, and neither she nor her family has come forward publicly.

Pressure mounted on Monday for Wu to resign. He said he would not seek re-election but would remain in office until the end of his term, in 2012. Then, Rep. Nancy Pelosi, D-Calif. and the House minority leader, called for an ethics investigation into the allegations.

"The well-being of my children must come before anything else," he wrote in his statement. "With great sadness, I therefore intend to resign effective upon the resolution of the debt ceiling crisis. This is the right decision for my family, the institution of the House, and my colleagues."

His exact departure date is uncertain. Lawmakers in Washington are racing against an Aug. 2 deadline to raise the nation's debt ceiling. Wu has been voting in Washington but has largely remained sequestered from the news media.

Wu's resignation marks the second time in two months that a Democratic congressman has been forced from office over allegations of sexual improprieties. Former Rep. Anthony Weiner, of New York, resigned on June 16 after denying and then acknowledging that he had sent sexually explicit online messages to at least six women.

Wu has been under fire for months as he fought earlier allegations of a mental breakdown after a divorce last year. In February, several staff members quit after describing erratic behavior and unwanted emails that included a picture of Wu dressed in a tiger outfit.