WASHINGTON — President Barack Obama on Friday nominated Sen. John Kerry as his next secretary of state, elevating the longtime lawmaker and foreign policy expert to the top diplomatic job he had coveted.

“He is not going to need a lot of on-the-job training,” Obama said, standing alongside Kerry at the White House. “Few individuals know as many presidents and prime ministers or grasp our policies as firmly as John Kerry.”

If confirmed by the Senate, Kerry would replace Secretary of State Hillary Rodham Clinton, who plans to leave Obama’s second-term Cabinet early next year. Clinton, who is recovering from a concussion sustained in a fall, did not attend the Roosevelt Room announcement.

In a statement, Clinton said, “John Kerry has been tested — in war, in government, and in diplomacy. Time and again, he has proven his mettle.”

The 69-year-old Democrat is expected to be easily confirmed by his Senate colleagues. He would be the first of what are expected to be several new faces on Obama’s national security team, including a new defense secretary and director of the Central Intelligence Agency.

The son of a diplomat, Kerry has served as chairman of the Senate Foreign Relations Committee and is a decorated Vietnam veteran who was critical of the war effort when he returned home to the United States. He has represented Massachusetts in the Senate since 1985.

“John’s entire life has prepared him for this role” said Obama, who praised Kerry for his belief that the country must harness “all elements of American power.”

The president picked Kerry for the post even though his nomination could create a political problem in Massachusetts. Republicans are eyeing the Senate seat Kerry will vacate after five terms, and recently defeated GOP Sen. Scott Brown would be a favorite in his party for the job.

Kerry was the Democratic nominee for president in 2004, losing a close election to incumbent George W. Bush.

Kerry’s only other rival for the job, U.N. ambassador Susan Rice, faced harsh criticism from congressional Republicans for her initial accounting of the deadly September attack on Americans in Benghazi, Libya. Obama vigorously defended Rice, a close friend and longtime adviser, but GOP senators dug in, threatening to hold up her nomination if the president tapped her for the post.

Rice withdrew her name from consideration last week, making Kerry all but certain to become the nominee. People familiar with the White House’s decision-making said support within the administration was moving toward Kerry even before Rice pulled out.

The president is also expected soon to nominate a new defense secretary to take over for retiring Leon Panetta and a new director of the Central Intelligence Agency to replace former spy chief David Petreaus, who resigned last month after admitting to an affair with his biographer.

Kerry, the chairman of the Senate Foreign Relations Committee, has long sought the nation’s top diplomatic post. Obama considered him for the job after the 2008 election before picking Clinton in a surprise move.

Since then, Obama has dispatched Kerry around the world on his behalf numerous times, particularly to tamp down diplomatic disputes in Afghanistan and Pakistan. He was also part of Obama’s debate preparations team during the 2012 election, playing the role of Republican challenger Mitt Romney in mock debates.

Kerry also won praise from Obama aides for his sharp national security-focused speech at the Democratic National Convention in August. He memorably told delegates: “Ask Osama bin Laden if he’s better off now than he was four years ago.”

Kerry, who has a consistent pro-Israel voting record, has nonetheless been among the sharpest congressional critics of Israel’s blockade of the Gaza Strip, and is a fierce opponent of West Bank settlement expansion.

He was also a leading critic of what he said was unsuccessful presidential candidate Mitt Romney’s overly aggressive stance on Iran, declaring in March, after Romney published an op-ed slamming Obama’s “feckless” approach, that “Talk has consequences, and idle talk of war only helps Iran by spooking the tight oil market and increasing the price of the Iranian crude that pays for its nuclear program.”

A frequent visitor to Israel, Kerry’s last trip was eight months ago, when he met with President Shimon Peres and with Prime Minister Benjamin Netanyahu soon after the death of Netanyahu’s father. He said on that trip that Israel should have “no doubt” about Obama’s commitment to thwarting a nuclear Iran.

When he ran for president in 2004, losing to Bush, Kerry won 74% of the Jewish vote, according to Gallup polling.

Before nominating Kerry, the White House consulted with congressional Democrats about the fate of the Senate seat he has held for five terms. An open seat in Massachusetts could give recently defeated Republican Sen. Scott Brown a chance to win back a job in Washington.

Democrats have sought to assure the White House that the party has strong potential candidates in the state that could keep Kerry’s seat from falling into Republican hands.

Kerry has pushed the White House’s national security agenda in the Senate with mixed results. He ensured ratification of a nuclear arms reduction treaty in 2010 and most recently failed to persuade Republicans to back a U.N. pact on the rights of the disabled.

As the nation’s top diplomat, Kerry will be tasked with not only executing the president’s foreign policy objectives, but also shaping Obama’s approach. The senator offered some insight into his world view on Thursday during a Senate Foreign Relations committee hearing he chaired on the deadly September attack on a U.S. consulate in Benghazi, Libya.

Kerry called on Congress to put enough money into America’s foreign policy objectives and said doing so is an investment “in our long-term security and more often than not it saves far more expensive expenditures in dollars and lives for the conflicts that we failed to see or avoid.”

And he emphasized the importance of U.S. diplomats being able to work freely in places like Benghazi, despite its dangers.

“There will always be a tension between the diplomatic imperative to get ‘outside the wire’ and the security standards that require our diplomats to work behind high walls,” he said. “Our challenge is to strike a balance between the necessity of the mission, available resources and tolerance for risk.”

Obama and Kerry have developed close ties in recent years. It was Kerry, during his 2004 presidential run, who tapped Obama as the party’s convention keynote speaker, a role that thrust the little-known Illinois politician into national prominence.

Kerry served on Obama’s debate preparation team during the 2012 election, playing Republican challenger Mitt Romney in mock debates.

“Nothing brings two people closer together than two weeks of debate prep,” Obama joked on Friday. “John, I’m looking forward to working with you rather than debating you.”

Former Republican Sen. Chuck Hagel is a front-runner for the Pentagon post, but has been dogged by questions about his support for Israel and where he stands on gay rights, with critics calling on him to repudiate a comment in 1998 that a former ambassadorial nominee was “openly, aggressively gay.”

Hagel apologized for that comment Friday.

Former Pentagon official Michele Flournoy and current Deputy Defense Secretary Ashton Carter are also under consideration to replace Panetta. Obama is also considering promoting acting CIA Director Michael Morell or naming White House counterterrorism adviser John Brennan as the nation’s spy chief.