Mitt Romney tells supporters in a conference call that he will not run for president in 2016. (The Washington Post)

Mitt Romney told supporters Friday that he would not run for president in 2016, ending three weeks of public speculation and sparing the Republican Party a potentially bruising nominating battle between its past nominee and its rising stars.

“After putting considerable thought into making another run for president, I’ve decided it is best to give other leaders in the party the opportunity to become our next nominee,” Romney said in a statement he read to supporters on a conference call Friday morning.

Romney insisted that he would have had enough support from potential donors to be “more than competitive” and that the positive reaction he heard from Republican activists was “surprising and heartening.” He noted that he led the GOP field in recent public polls.

“I am convinced that we could win the nomination, but fully realize it would have been difficult test and a hard fight,” Romney said in remarks he delivered by phone from New York with his wife, Ann, by his side.

“You can’t imagine how hard it is for Ann and me to step aside, especially knowing of your support and the support of so many people across the country,” he added. “But we believe it is for the best of the party and the nation.”

Mitt Romney visits with diners at Little Dooey, a barbecue restaurant in Starkville, Miss., on Wednesday. (Rogelio V. Solis/AP)

Romney spoke for four minutes before signing off by telling supporters, “Bye bye.” He encouraged his allies to “stay engaged” in the 2016 campaign and to “feel free” to sign up with any of the other potential candidates.

Romney had been publicly weighing a third run at the White House for three weeks after telling a group of former campaign donors in New York on Jan. 9 that he still wanted to be president.

His dalliance invited a barrage of critical reaction from many Republican leaders, conservative commentators and major donors. The influential Wall Street Journal editorial page was particularly harsh, describing Romney’s political profile as “protean,” his political team as “mediocre” and his managerial skills as questionable based on his 2012 loss to President Obama.

Romney’s advisers discounted the impact those criticisms would have on the former Massachusetts governor’s ultimate decision. Instead, they said earlier, Romney was spending his time as he always had under such circumstances: gathering data, speaking to as many people as possible and then weighing the evidence before making any final decision.

Romney’s decision to forgo a third run came after a lengthy meeting of Romney’s inner circle in Boston last Friday, during which they evaluated feedback from former campaign donors and activists in key early voting states. The assessment was realistic — “we were not Pollyanaish,” one adviser said — and included reports from Iowa, New Hampshire and South Carolina, where Romney would have lost some key precinct leaders although still had considerable support.

Many participants left that session convinced that it was all but certain he would run again. In the end, however, Romney balked. One person close to the family said he made up his mind last weekend, but wanted to give himself the week to think it over before making his decision final.

“It’s a very personal decision,” said a senior adviser, who like others interviewed requested anonymity to speak candidly. “All the political metrics were positive. Ultimately, running for president, you just have to feel right about it in your heart. They just didn’t feel it was right. He’s a happy person. He’s not a needy, desperate guy.”

Ron Kaufman, a longtime Romney adviser and confidant, said he and others in the circle believed Romney would have made an excellent president and that he was sad the country would not have the chance for him to serve.

“As much as you might want to be the candidate, you sometimes realize you can be more effective at helping fulfill a different role,” Kaufman said. “He’s an amazing person and he doesn’t need to have the captain’s seat.”

Romney, in recent conversations with intimates as well as his public appearances, sounded eager to step back into the political ring. Those who have spoken to Romney said they came away from the conversations believing he was likely to run again for several reasons, including that he views the emerging GOP field of contenders as too weak to defeat likely Democratic candidate Hillary Rodham Clinton, that he believes he would be a better candidate after his experiences in 2012, and that he sensed an opportunity to win.

Romney signaled that if he ran again, his campaign would focus on three themes: foreign policy, expanding opportunities for the middle class and eradicating poverty.

In Friday’s call, Romney said: “I also believe with the message of making the world safer, providing opportunity for every American regardless of the neighborhood they live in, and working to break the grip of poverty, I would have the best chance of beating the eventual Democrat nominee, but that’s before the other contenders have had the opportunity to take their message to the voters.

“I believe that one of our next generation of Republican leaders — one who may not be as well-known as I am today, one who has not yet taken their message across the country, one who is just getting started — may well emerge as being better able to defeat the Democrat nominee. In fact, I expect and hope that to be the case.”

Romney’s announcement comes as former Florida governor Jeb Bush has taken aggressive steps toward a campaign, traveling around the country meeting with donors and other party figures, many of them loyal to Romney in 2012. Bush has set up a leadership PAC and a super PAC, both with the name “Right to Rise,” and has been test-driving a campaign message centered squarely on middle-class opportunity.

Bush wrote in a Facebook post on Friday that Romney “has been a leader in our party for many years” and that “there are few people who have worked harder to elect Republicans across the country than he has.”

“Though I’m sure today’s decision was not easy, I know that Mitt Romney will never stop advocating for renewing America’s promise through upward mobility, encouraging free enterprise and strengthening our national defense,” Bush added. “Mitt is a patriot and I join many in hoping his days of serving our nation and our party are not over.”

Another potential candidate, Sen. Marco Rubio (R-Fla.), said of Romney, “He certainly earned the right to consider running, so I deeply respect his decision to give the next generation a chance to lead. I wish him, Ann and his entire family the best and hope he will continue to serve our country and his community as he’s done throughout his life.”

Romney is scheduled to have dinner Friday night with New Jersey Gov. Chris Christie (R), who also is eyeing a 2016 run, a get-together was planned before Romney’s announcement. Romney was already scheduled to be in the New York area Friday, because he and Ann are slated to attend a lunchtime function in Manhattan.

While the two men are friends, longtime supporters do not expect Romney to throw his weight behind Christie or any other candidate in the immediate future.

In a speech to the Republican National Committee meeting in San Diego two weeks ago, Romney said that dealing with wage stagnation, the middle class economic squeeze and lifting people out poverty should be among the handful of pillars for a 2016 GOP campaign.

At the same meeting, Romney also signaled that, if he ran, he would be far more forthcoming about — and presumably comfortable with — his Mormon faith, which he largely avoided talking about in his first two campaigns. Romney told friends that he wanted to be a more authentic candidate if he ran in 2016 than he was in 2008 or in 2012.

This was Romney’s way of trying to tell people that the stereotype of him as a cold-hearted businessman was a false construct by his opponents, and that his faith and good works would show a more empathetic side to the public.

But Romney also dealt with some serious defections from his political operation and donor network. On Thursday, David Kochel, an adviser to Romney for more than a decade and his top strategist in Iowa, announced he would work instead for Bush. Should Bush launch a presidential campaign, Kochel is in line to become national campaign manager.

The Kochel move shook some in Romney’s orbit, which had included the former aide on some recent strategy talks and believed he would be on board with Romney in 2016. But two close Romney advisers said Kochel’s departure had no impact on his decision.

Many longtime figures in Romney’s political orbit advised him through his deliberations, including former Utah governor Michael O. Leavitt, strategist Stuart Stevens, close friend Bob White, political advisers Kaufman, Beth Myers, Eric Fehrnstrom and Peter Flaherty, and policy adviser Lanhee Chen.

Romney’s announcement Friday comes a day before arriving in Washington for the annual dinner of the exclusive Alfalfa Club, where he is being inducted as a new member.

Seven Bush family members are members, but none is attending the annual dinner on Saturday night. As a result, one member says, attention will focus heavily on Romney. The former Massachusetts governor will be seated at the head table next to Wisconsin Gov. Scott Walker and Indiana Gov. Mike Pence, both potential 2016 rivals.

Matea Gold and Tom Hamburger contributed to this report.