In choosing to resign from the governor’s office rather than cling to the post, Eliot Spitzer is trying to do something he probably wishes he had done earlier: think of his family first.

When it became clear he was entangled in a federal prostitution prosecution, Mr. Spitzer’s initial reaction was to step down, but one of his aides, Lloyd Constantine, persuaded him to hang on. Other aides, however, said he needed to protect his family and resign. Mr. Spitzer and his wife have three teenage daughters.

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A source with knowledge about what was going on in the apartment said protecting the family was the paramount factor in Mr. Spitzer’s decision to resign.

Mr. Spitzer’s professional future is uncertain, and he offered limited insight into his post-gubernatorial plans yesterday when, wearing a dark pinstriped suit and a somber expression, he offered an apology.

Speaking in a steady, unwavering voice, but not addressing the allegations against him in detail, Mr. Spitzer said, “As I leave public life, I will first do what I need to do to help and heal myself and my family. Then I will try once again, outside of politics, to serve the common good and to move towards the ideals and solutions which I believe can build a future of hope and opportunity for us and for our children,” he said.

Friends of the 48-year-old Mr. Spitzer have recently worried about whether he is a danger to himself, an aide to Mr. Spitzer said.

A managing director at the legal recruiting firm BCG Attorney Search, Danice Kowalczyk, said Mr. Spitzer, a lawyer by training and profession who has worked for several prominent law firms, could try to jump on the lecture circuit, get into publishing, or return to a law firm. Mr. Spitzer graduated from Horace Mann, Princeton University, and Harvard Law School.

Ms. Kowalczyk cautioned, however, that not everyone would be eager to extend an offer.

“There are some law firms that will be able to look at him as a human being and separate him from the politician. There will be others who won’t be able to do that, who can’t get past what he did,” she said.

Mr. Spitzer is facing the possibility of criminal prosecution in connection with his alleged ties and involvement in the prostitution ring. If Mr. Spitzer were convicted of a felony, he would be disbarred.

Yesterday’s resignation capped off a dizzying plummet from power for Mr. Spitzer, a hard-charging lawyer who ascended to office in a landslide victory less than 15 months ago.

“I am deeply sorry that I did not live up to what was expected of me,” he said yesterday, with his wife, Silda Wall Spitzer, standing by his side. “To every New Yorker and to all those who believed in what I tried to stand for, I sincerely apologize.”

The last New York governor to leave office in disgrace was William Sulzer, who was impeached in 1913 after allegedly dipping into his campaign funds for personal use.

Mrs. Spitzer did not speak during her husband’s press conference in his Midtown Manhattan government office, but kept her eyes fixed on him during portions of the speech.

Mr. Spitzer said he had spent the past few days beginning to atone for his private failings with his wife, his children, and his entire family.

“The remorse I feel will always be with me. Words cannot describe how grateful I am for the love and compassion they have shown me. For those to whom much is given, much is expected. I have been given much: the love of my family, the faith and trust of the people of New York, and the chance to lead this state,” he said.

Mr. Spitzer, a former state attorney general who took on Wall Street, said that over the course of his public life he has insisted that people, regardless of their position or power, take responsibility for their conduct.

“I can and will ask no less of myself. For this reason, I am resigning from the office of governor,” he said. The resignation will be effective Monday. Mr. Spitzer said that was at the request of Lieutenant Governor David Paterson, who will succeed him.

Mr. Spitzer spoke for about two and a half minutes yesterday and did not take questions from the 100 or so reporters crowded into room where he delivered his remarks.

On his way out, a reporter called out to ask the governor if he had ever thought it would come to this and another asked Mrs. Spitzer to see if she was going to leave her husband. The Spitzers ignored them.

Mr. Spitzer sent a resignation letter typed on his official State of New York letterhead, with his name above the title governor in the upper left hand corner, to the speaker of the Assembly, Sheldon Silver, and the state Senate majority leader, Joseph Bruno.

“Dear Speaker Silver and Majority Leader Bruno,” the letter, dated March 12, said. “I am writing to advise you that I am resigning my position as Governor of the State of New York effective at 12:00 noon on Monday, March 17, 2008. Sincerely, Eliot Spitzer Governor.”

Mr. Paterson, who will be sworn in on Monday, said yesterday that he was saddened by the turn of events. He is on the brink of becoming the first black governor in the state and apparently the first blind governor in American history.

“On a personal level Governor Spitzer and Silda have been close and steadfast friends,” he said in a statement. “As an elected official the Governor has worked hard for the people of New York. My heart goes out to him and to his family at this difficult and painful time.”

He added: “It is now time for Albany to get back to work as the people of this state expect from us.”

Basil Paterson, a former state senator from Harlem and secretary of state of New York who is the father of David Paterson, and Carl McCall, a former state comptroller, were in Albany yesterday to help with the transition.

Mr. Spitzer’s cabinet also held a meeting in Albany yesterday, led by the governor’s chief of staff, Richard Baum, and Mr. Paterson’s chief of staff, Charles O’Byrne.

A man identified in a federal affidavit as “Client 9,” who is believed to be Mr. Spitzer, was caught on a wiretap arranging to meet with a woman named Kristen at the Mayflower hotel in Washington on February 13. The woman was described in a report on the New York Times Web site as a 22-year-old high school dropout from New Jersey with a history of drug abuse.

Mr. Spitzer allegedly spent $4,300 on the rendezvous. Several newspaper reports have claimed that the governor had been meeting with prostitutes for as many as 10 years and spent as much as $80,000.

After a brief public statement on Monday immediately following the first disclosure of his alleged ties to the prostitution ring, Mr. Spitzer spent Tuesday holed up in his Fifth Avenue apartment, wavering between resigning and defiantly clinging to the office.

As Mr. Spitzer announced his resignation yesterday, Mayor Bloomberg was in the middle of a press conference in Brooklyn. He showed sympathy for the governor, and expressed confidence in his replacement. He also rejected the idea that he might run for the state’s highest office.

“My thoughts are with the governor and his family at this difficult time and I think what we have to do now is to move forward,” Mr. Bloomberg said. “The state has to have an effective government and they will be effective.”

The governor did not call the mayor to inform him of his decision, Mr. Bloomberg said, but the mayor spoke later in the day to Mr. Paterson, who invited Mr. Bloomberg to attend the swearing-in ceremony. Mr. Bloomberg said he’d be there.

Asked whether Mr. Spitzer should face jail time for his alleged involvement in a prostitution ring, Mr. Bloomberg said, “that’s up to the legal authorities.”

The mayor had kind words for Mr. Paterson, saying he thinks he understands the responsibilities of the office and will work hard.

“He’s somebody that everybody says nothing but nice things about, and I think he can pull this state together and carry it through what’s obviously a very difficult period for all of us,” he said.

Mr. Bloomberg appeared upbeat when addressing reporters, cracking a large smile when asked about a Quinnipiac University poll released yesterday showing that 57% of New York City voters think he should stay in politics after his term expires.

The poll also found that 73% of city voters think Mr. Bloomberg would make a good governor. With Albany in turmoil, speculation has increased that he may run for governor. The mayor denied harboring such ambitions.

“I have no interest in running for governor. I’ve said that repeatedly,” he said.

Mr. Silver, who some political insiders predict will exert more influence after Mr. Spitzer’s exit, said yesterday was “a painful day for New York.”

“Now is the time to pray for the Spitzer family. Now is the time to move forward with the people’s business,” he said in a statement.

Mr. Bruno, who was a political adversary of Mr. Spitzer’s, said the events of the past few days were “a crisis unlike any other ever faced in State history.”

He said in a statement that his heart goes out to Mrs. Spitzer and the Spitzer family, adding that the governor “must deal with his own problems in his own way.”

Senator Schumer, in Washington yesterday, said during an interview on CNN that public officials should be held to the highest standards.

When asked if Mr. Spitzer should be punished, Mr. Schumer said the governor was undergoing plenty of punishment right now. He declined to comment on the possibility that the governor will face prosecution.

Senator Clinton said in a statement that she is saddened by the turn of events and said her thoughts are “with Governor Spitzer’s family during this painful time.”