Greg Swiercz/South Bend Tribune, via Associated Press

Updated | 1:42 p.m.

Gov. Mitch Daniels of Indiana said early Sunday that he would not become a candidate for the Republican presidential nomination, telling supporters in an e-mail message that concerns from his family were the overriding factor in deciding to stay out of the race.

“In the end, I was able to resolve every competing consideration but one,” Mr. Daniels wrote. “The interests and wishes of my family is the most important consideration of all. If I have disappointed you, I will always be sorry.”

His announcement answers one of the most highly anticipated questions about the 2012 Republican campaign, but introduces new uncertainty into the race. He is the latest in a string of prominent Republicans to decline a presidential bid, leaving the field without a clear front-runner less than eight months before the first voting could begin.

Mike Huckabee, the former Arkansas governor; Gov. Haley Barbour of Mississippi; and Donald J. Trump, the businessman and reality TV star, have all announced in recent weeks that they would not seek the Republican nomination. Sarah Palin, a former governor of Alaska, has yet to declare her intentions. But the rest of the field is coming together.

Tim Pawlenty, a former governor of Minnesota, is scheduled to announce his candidacy on Monday. The decision by Mr. Daniels to stay out of the race could elevate the prospects for Mr. Pawlenty, who is trying to become a leading alternative to Mitt Romney, who sought the party’s nomination in 2008 and plans to run again.

Mr. Daniels delivered the news in an unusual way, explaining his decision in a telephone call to a small circle of confidants late Saturday. A few hours later, he sent a brief message to top contributors and political leaders who had expressed an interest in his candidacy. The e-mail was sent after midnight by Eric Holcomb, chairman of the Indiana Republican Party and one of Mr. Daniels’ closest political advisers.

“I hope this reaches you before the public news does,” Mr. Daniels wrote. “If so, please respect my confidence for the short time until I can make it known to all.”

The message, which was obtained by The New York Times, was confirmed by another aide to Mr. Daniels in Indianapolis. It was a crushing blow to admirers who had rallied around the idea of a Daniels candidacy, including more than 1,000 Republicans who filled a hotel ballroom in Indianapolis last week and held signs declaring: “Run Mitch Run.”

For weeks, Mr. Daniels has inched closer to entering the Republican race, declaring recently at the state party dinner: “I’m not saying I won’t do it.” And several party leaders urged him to run, saying that his experience on fiscal issues would strengthen the ticket.

In his brief message early Sunday, Mr. Daniels acknowledged that his decision would be a disappointment to many supporters, but he implored them to understand his rationale.

“If you feel that this was a non-courageous or unpatriotic decision, I understand and will not attempt to persuade you otherwise,” Mr. Daniels wrote. “I only hope that you will accept my sincerity in the judgment I reached.”

Mr. Daniels had been widely expected to make his decision known this week. In an interview with reporters last Thursday in South Bend, Ind., Mr. Daniels signaled that the time had come for him to disclose his intentions.

“People have been very patient and understanding,” he said, “but I have a sensitivity that I owe people an answer.”

Mr. Daniels expounded on his decision in a statement to The Indianapolis Star, saying that the concerns of his wife and his four daughters were the main factors in his determination.

“On matters affecting us all, our family constitution gives a veto to the women’s caucus, and there is no override provision,” Mr. Daniels said. “Simply put, I find myself caught between two duties. I love my country; I love my family more.”

Mr. Daniels kept his own counsel on his decision, aides said, with many of his closest political advisers unaware of his intentions. But he signaled his concerns nearly every time that he spoke about the race publicly.

His wife, Cheri, has made no secret of her distaste for politics. She did not campaign for her husband during his two races for governor. This is her second marriage to Mr. Daniels. In 1993, she left her husband and four daughters and moved to California to marry another man — only to remarry Mr. Daniels in 1997.

Many supporters assumed that his family was warming to the idea of a presidential campaign, particularly when Mrs. Daniels delivered a rare political speech at the state Republican Party dinner on May 12 in Indianapolis. But after the appearance, Mrs. Daniels made clear that the family had not signed off on a campaign, saying: “You have good days and bad days. One day you feel one way, another day you might feel differently.”

For his part, when asked directly whether he wanted to be president, Mr. Daniels said: “I haven’t decided yet.”

A few minutes later, when pressed again, he added: “You have to decide if this is really the way you’d like to spend – maybe – the rest of your life.”

While Mr. Daniels said that family concerns ultimately kept him from the race, he issued a separate statement to The Indianapolis Star seeking to clarify one period of his family’s history. The couple got married in 1978, divorced in 1994, and remarried in 1997. Mrs. Daniels briefly moved to California, while Mr. Daniels took primary care of their four girls.

“The notion that Cheri ever did or would abandon her girls or parental duty is the reverse of the truth and absurd to anyone who knows her, as I do, to be the best mother any daughter ever had,” Mr. Daniels said in the statement. He added, “Until we remarried, we shared custody fully, the girls dividing their time between the two homes.”

Mr. Daniels, a former budget director in the White House under President George W. Bush, had secured the fund-raising commitments and political support from a large contingent of alumni from the Bush network. In recent days, aides said, several contributors sent word to Mr. Daniels that they needed an answer soon.

The message from Mr. Daniels early Sunday indicated that he appreciated the support.

“The counsel and encouragement I received from important citizens like you caused me to think very deeply about becoming a national candidate,” he wrote.

He added, “Many thanks for your help and input during this period of reflection. Please stay in touch if you see ways in which an obscure Midwestern governor might make a constructive contribution to the rebuilding of our economy and our Republic.”

Both supporters and rivals praised Mr. Daniels on Sunday.

Newt Gingrich, the former house speaker and a Republican presidential candidate, called Mr. Daniels “a terrific talent” and “one of the great reform governors in this country.” “He would have been a very formidable competitor. I mean, I really thought he would be in the front-runners from day one if he had decided to run,” he told CBS’s “Face the Nation” on Sunday.

Representative Paul Ryan of Wisconsin, the chairman of the House Budget Committee, who has also been a keen proponent of fiscal austerity, said he was disappointed that Mr. Daniels had dropped out. He dismissed any suggestion that he himself was considering running. “I am disappointed. I think his candidacy would have been a great addition to this race and I think it’s unfortunate that he’s not going to run,” he told NBC’s “Meet the Press.”

Mark Lubbers, a long-times associate and adviser to Mr. Daniels, told The Indianapolis Star it was ironic that Mr. Daniels had ultimately made family a priority over politics, since in the past, he had come under criticism by some on the religious right for making economics more important than divisive social issues like abortion. “I think it’s fabulously ironic that the candidate criticized by the family values caucus has made a decision based 100 percent on family values,” he said.

Mr. Holcomb, who managed the governor’s 2008 re-election campaign, told The Star that his emotions were “bittersweet.” He said the nation would miss a unique talent who is able to connect with voters while also possessing a wonkish ability to work on nuanced policies.

“For his 800-pound brain, he’s got a populist instinct that is just remarkable,” Mr. Lubbers said.

The Indiana Democratic Party said Mr. Daniels would have brought a degree of gravitas to the race. “We’ve disagreed with Mitch Daniels myriad times, but there’s no doubt that his decision not to enter this race is a loss for Republicans,” said Dan Parker, the chairman. “Daniels would have brought a serious tone to a G.O.P. field that’s thus far been characterized by silliness and distraction.”

Mr. Daniels, who is popular in his own state, came to prominence in Indiana as an austerity-minded fiscal conservative who privatized some government services, including the construction of highways. During his first term, he became known as “Governor Privatize,” a name he disliked. Mr. Bush nicknamed him “the Blade” in reference to his acumen as a cost-cutter.

A political assistant in the White House under President Ronald Reagan, he subsequently became an executive at Eli Lilly in his native Indiana. In 2004, he was elected governor; he was re-elected, more narrowly, in 2008.

Mr. Daniels’s fiscal prudence was considered a key asset in elections where the deficit is expected to feature prominently. As governor, he has reduced the number of state workers by 18 percent and held spending growth below inflation. Under his stewardship, Indiana finds itself in better fiscal health than many other states.

In an interview on Thursday in Indiana, Mr. Daniels said that he was still actively considering the race. When asked whether it was a painful decision to make, he said: “It’s complicated.”

Dan Bilefsky contributed reporting from New York.

