In a stunning announcement made with his wife at his side, New Jersey’s governor, James McGreevey, said yesterday he had an affair with a man and would resign in November.

“My truth is that I am a gay American,” the twice-married father of two told reporters at a hastily called press conference at the statehouse in Trenton, N.J. “Shamefully, I engaged in an adult consensual affair with another man which violates my bonds of matrimony. It was wrong, it was foolish, it was inexcusable.”

The unexpected declaration came after a former aide, Golan Cipel, threatened to file a sexual harassment suit against Mr. McGreevey, 47, unless the governor paid him millions of dollars, an adviser to the governor said. He characterized the threat as “a clear extortion attempt.”

Mr. McGreevey, a Democrat, will resign November 15, effectively blocking any chance for a special election in which a Republican governor could be elected. The state Senate president, Democrat Richard Codey, will finish out Mr. McGreevey’s term, which ends in January 2006.

Mr. McGreevey, a former mayor of Woodbridge, said he would resign because the affair and his sexuality leaves the governor’s office “vulnerable to rumors, false allegations, and threats of disclosure.”

“It makes little difference, as governor, that I am gay,” Mr. McGreevey said. “Given the circumstances surrounding the affair and its likely impact on my family and my ability to govern, I have decided the right course of action is to resign.”

Throughout the press conference, Mr. McGreevey’s wife, Dina, stood by his side, along with his parents. The governor, a Catholic who was once an altar boy, was emotional as he spoke about his sexuality, telling the public he always felt that he was somehow different.

“From my early days in school until the present day, I acknowledged some feelings, a certain sense that separated me from others,” the governor said. “I forced what I thought was an acceptable reality onto myself – a reality which is layered and layered with all the quote ‘good things’ and all the quote ‘right things’ of typical adolescent and adult behavior.”

The announcement effectively ends Mr. McGreevey’s political career, which has been plagued by scandals involving some of the governor’s closest confidants, including his biggest contributor, Charles Kushner, a real estate developer accused last month of trying to blackmail a grand jury witness in a campaign finance investigation.

Two sources close to Mr. McGreevey said the man involved in the affair was Mr. Cipel, a 35-year-old Israeli poet who worked briefly for the governor as a $110,000-a-year homeland security adviser despite having no security experience.

Both sources, senior advisers to Mr. McGreevey, said Mr. Cipel threatened Mr. McGreevey several weeks ago that unless he was paid “millions of dollars,” he would sue the governor for sexual harassment.

Mr. McGreevey hired Mr. Cipel in February 2002. Mr. Cipel resigned from the position a month later after the political outcry, but continued to work for the administration, at the same salary, with a vague job description, according to published reports.

Mr. Cipel finally left the governor’s office in August 2002 to work for a private public relations firm that represented Mr. Kushner. Mr. Cipel could not be reached for comment.

Rumors have long circulated that the New Jersey governor was gay, and it was unclear whether his wife would seek a divorce. Mr. McGreevey has two daughters, one from his second marriage, and one from his first wife, Kari, who lives in British Columbia with the child.

According to the Web site of New Jersey Capital Report, Mr. McGreevey took time out from his transition plans to accompany Mr. Cipel on a last minute walk-through of a West Windsor townhouse Mr. Cipel was about to purchase.

Capital Report quoted the seller, Elaine Dietrich, as saying Cipel “want ed to have a place that was in close proximity to where the governor was because he was a personal adviser on call 24 hours a day.”

Mr. McGreevey’s political stances on gay issues are a mixed bag. He signed into a law that allowed domestic partners to make medical decision for each other and file joint state tax returns, but fell short of legalizing gay marriage.

But when New Jersey’s attorney general said gay marriage in the state was illegal, Mr. McGreevey skirted the issue. “The state is bound by the court and the court has held that it is not legal,” he told reporters at the time. “Ultimately we’re a nation of laws and we need to abide by the laws.”

On the political front, Republicans yesterday accused Mr. McGreevey of posturing, saying he was waiting to resign so that Democrats could hold on to the governor’s office.

“His resignation is in the best inter est of the people of New Jersey; however, he should be resigning now rather than delaying his resignation,” said the executive director of the New Jersey Republican State Committee, Brian Nelson. “Waiting until November is “political gamesmanship to avoid holding a special election.”

The governor’s advisor denied that claim, saying Mr. McGreevey wants to make a smooth transition. “You can’t just walk out,” he said.

“My heart goes out to Jim Mc-Greevey and his family during this difficult personal time,” Mr. Codey, an undertaker who will take the reins from McGreevey in November, said in a statement.

Mr. McGreevey’s decision to out himself and declare his resignation came on the same day that the California Supreme Court said a state law defines marriage as between a man and woman and voided all of the nearly 4,000 gay marriages performed in San Francisco this year. The court also ruled unanimously that the city’s mayor does not have the authority to issue licenses to same-sex couples.

Despite the setback in California, gay-rights activists said Mr. Mc-Greevey’s decision to come out of the closet was one small step forward in their community.

“I think that whenever a prominent person comes out of the closet it paves the way for more people to come out. Certainly no one envies Governor Mc-Greevey with the circumstances in which he came out of the closet,” said the executive director of the Lesbian, Gay, Bisexual & Transgender Community Center, Richard Burns. “But it again emphasizes the message that gay people are everywhere.”

Mr. McGreevey is the second governor to resign in the tri-state area. His announcement comes two months after Connecticut’s governor, John Rowland, was forced out of office.