Mr. Filner, 70, in a hastily called news conference in San Diego, apologized to his staff, his city, his supporters and "most of all, to the women I have offended."
"Words alone are not enough," he said, in an announcement that he had to make twice after the sound system failed, creating an extended, awkward silence soon after he stepped up to the microphone to speak.
"I am responsible for this conduct," Mr. Filner said after leaving the room while the microphone was replaced, and then returning a few minutes later. "I must take responsibility for my conduct by taking action so that such conduct does not ever happen again. So beginning on August 5, I will be entering a behavior counseling clinic to undergo two weeks of intensive therapy."
What was perhaps most striking about Mr. Filner's statement, which lasted less than three minutes, was that he did not entertain the idea of resigning. His news conference came the day after four more women publicly accused the mayor of sexual harassment, in interviews on KPBS News, and when the San Diego County Democratic Party voted for him to step aside. In all, seven women have publicly accused the mayor of sexual harassment.
Indeed, Mr. Filner indicated that he would keep a hand in City Hall even from the seclusion of his treatment program, saying he planned to be briefed every morning and every evening on what was taking place there.
"I must become a better person," he said.
Mr. Filner's appearance Friday is not the first time, since the allegations first arose in mid-July, that he has attempted to defuse them with his remarks. That said, he went considerably further during the news conference than he had before in his apologies.
"The behavior I have engaged in over many years is wrong," Mr. Filner said. "My failure to respect women and the intimidating contact I engage in at times is inexcusable. It has undermined what I have spent my whole professional life doing and working on, fighting for equality and justice for all people."
It remains to be seen whether Mr. Filner's decision to enter a treatment program will be enough to satisfy the growing tide of people — including some of his own supporters — demanding his resignation. City officials said there is no apparent ground for impeachment. But there has been talk of waging a recall effort that would be time-consuming and costly.
Todd Gloria, the president of the City Council and a Democrat, said he was not satisfied with Mr. Filner's announcement and that the mayor needed to leave.
"It's not enough," he said. "The people of this city want this mayor to resign and they want him to do it quickly. His prolonging of this pain is simply unacceptable, and nothing will change as a result of this leave of absence he's taking."
Mr. Gloria said the City Council would"do our best to handle this situation. But we can't be efficient and effective governmental branch until the mayor resigns."
But Francine Busby, the chairwoman of the San Diego County Democratic Party, which voted overwhelmingly on Thursday to ask for Mr. Filner's resignation, said she might be willing to give him some room.
"Democrats aren't going to give him a pass, but may be willing to give him the benefit of the doubt because we've waited so long, nearly 20 years, for a mayor who could put forward a progressive agenda," she said.
"But this doesn't erase what he's done," she said. "It doesn't end the distraction. I don't know if it's enough at this point."
This latest development in Mr. Filner's career marked a sharp turn what had been a short but intense tenure as mayor. He took office last December, vowing to upend San Diego City Hall. Mr. Filner is the city's first Democratic mayor in 20 years, and his campaign had been promoted and embraced by labor organizations, Democrats and many progressive leaders
As soon as the first allegations were made, Mr. Filner acknowledged inappropriate behavior, in how he spoke to women and touched them, but said he had not been guilty of sexual harassment. The initial round of accusations was anonymous, and Mr. Filner said then he deserved due process and a fair hearing to make his case.
But over the past week, the seven women — people who worked for him as well as constituents — have come forward to complain, in detail, of sexual harassment by Mr. Filner.
The flood of accusations was accompanied by a steady crumbling of support for Mr. Filner from the city's political establishment. On Thursday night, the San Diego County Democratic Party called on Mr. Filner to step aside, joining members of Congress and the City Council and his largest supporter, Lorena Gonzalez, a state assemblywoman who was secretary-treasurer of the San Diego labor organization that pumped close to $2 million into his race.
The continuing scandal has captivated San Diego and frozen the government in place. Mr. Filner has repeatedly asserted that the city's business would not be hurt by the distractions of the charges, and repeatedly put out statements making it appear that it was business as usual. But he faced the departure of top people in City Hall, including his chief of staff, and cut down his public appearances as he found himself confronted with questions from reporters about the allegations.
The accusations against him were often presented in some detail; his former communications director talked about how he put her in what became known as a "Filner headlock" and whispered sexually inappropriate remarks into her ear. Mr. Filner, in a videotaped statement, described himself as physically expressive, calling himself a hugger and saying that he offered his embraces to both men and women.
San Diego has dealt with its share of municipal scandals over the years. Mr. Filner joins a line of mayors there who have stepped aside, including Richard M. Murphy, a Republican who was forced out of office in 2005 in the midst of a pension financing crisis that led San Diego to earn the nickname Enron-by-the-Sea.
Ian Lovett and Adam Nagourney reported from Los Angeles, and Rob Davis contributed reporting from San Diego.
