President Obama has picked Sen. John Kerry for secretary of State,hailing him as an extraordinary lawmaker who has played a central partin every major foreign policy debate of the last 30 years.

Kerry,chairman of the Senate Foreign Relations Committee and decorated Vietnamveteran, if confirmed by his colleagues in the Senate would replaceHillary Rodham Clinton if confirmed by his fellow senators.

"Today,I'm looking ahead to my second term and I'm very proud to announce mychoice for America's next secretary of State John Kerry," Obama said.The president added, "Over the years, John has earned the respect andconfidence of leaders around the world. He is not going to need a lotof on-the-job training."

Kerry'spath to the nomination cleared last week when another candidate --United Nations ambassador Susan Rice -- announced she would not pursuethe secretary of State post.

Kerry, who turned 69 this month, hashad lifelong involvement in foreign issues. The son of a foreign serviceofficer, Kerry fought in Vietnam and later became a leader of aveterans' group that opposed the war.

Elected lieutenant governorof Massachusetts in 1982, Kerry won his first U.S. Senate race two yearslater, and is currently in his fifth term. He secured the DemocraticParty's presidential nomination in 2004, but lost the general electionto incumbent President George W. Bush.

During his Senate years,Kerry opposed U.S. assistance to Nicaraguan rebels during the 1980s andcriticized the Iraq war during his 2004 presidential bid against Bush.

SinceObama's election, Kerry has worked to improve U.S. relations withAfghanistan President Hamid Karzai, and spoke with Pakistan leadersafter the 2011 raid that killed Osama bin Laden on Pakistani territory.

If confirmed as Secretary of state, Kerry's departure from the Senate sets up what could a pivotal political battle.

RepublicanScott Brown, who lost his Massachusetts Senate re-election bid inNovember to Elizabeth Warren, has expressed interested in running again.Among Democrats being mentioned as a Kerry replacement: Vicki Kennedy,the widow of long-time Sen. Edward Kennedy, D-Mass.

Over the years, Kerry has also played a key role in Obama's rise to the presidency.

Itwas Kerry who picked Obama, then a relatively unknown figure on thenational stage seeking a U.S. Senate seat, to give the keynote addressat the 2004 Democratic Convention. That speech launched Obama's nationalpolitical career, and Kerry stood in as Mitt Romney during thepresident's debate preparation earlier this year.

"Of course,nothing brings two people closer together than two weeks of debateprep," Obama joked. "John, I'm looking forward to working with youinstead of debating you."

When Obama sought the presidency in2008, Kerry endorsed him at a key moment -- after Obama lost the NewHampshire primary to Hillary Rodham Clinton.

Obama also considered Rice, a long-time aide, for the secretary of State job.

ButRice pulled out after Senate Republicans had criticized her forcomments after the Sept. 11 attack on the U.S. consulate in Benghazi,Libya, setting up the prospect of a tough Senate confirmation fight. In aseries of interviews, Rice attributed the attack to a protest of ananti-Islam video that got of hand; officials later called it anorganized terrorist attack.