* As secretary of state, he would face Syria, Iran challenges
* Kerry seen as able negotiator, cautious public speaker
* Decision-making likely to remain centered in White House
By Patricia Zengerle
WASHINGTON, Dec 21 (Reuters) - John Kerry gave up his presidential dreams after a narrow loss to Republican George W. Bush in the 2004 U.S. election, but forged a new identity as a congressional leader on foreign policy - and dutiful supporter of President Barack Obama.
Obama rewarded the five-term Massachusetts senator on Friday by nominating him to succeed Hillary Clinton as U.S. secretary of state.
Kerry, a patrician Yankee, will confront a raft of policy problems as the United States' top diplomat, ranging from the Syria crisis and impasse over Iran's nuclear program to mapping out the next phase of U.S. relations with prickly powers such as China and Russia.
He also will face the personal challenge of succeeding Clinton, who has become one of Obama's most popular and most visible Cabinet secretaries during her four years in office.
Obama's choice of Kerry comes after Susan Rice, the U.S. ambassador to the United Nations who had been the front-runner for the job, withdrew from consideration amid scathing Republican criticism of her handling of the attack on the U.S. consulate in Benghazi, Libya.
Even Republicans in Congress said they expect Kerry to sail through the confirmation process.
Kerry has sometimes served as Obama's special emissary in times of crisis. He flew to Afghanistan in 2009, when he helped talk President Hamid Karzai into agreeing to a runoff election, and to Pakistan in 2011 amid an uproar over a U.S. government employee who was arrested for killing two people allegedly trying to rob him.
But Obama has centralized national security decision-making in the White House and analysts say Kerry's selection could signal an even firmer White House hand in Obama's second term.
Kerry, known as an able negotiator and cautious public speaker, is likely to be put to the test soon after taking over at the State Department as two major U.S. foreign policy challenges move to the fore.
The 21-month uprising against Syrian President Bashar al-Assad appears to be nearing a tipping point as rebels advance, leaving Washington scrambling to map out policies to deal with everything from a power vacuum to the potential use of chemical weapons as a last-ditch defense by Damascus.
As senator, Kerry visited Damascus repeatedly prior to the outbreak of protests and was a proponent of U.S. re-engagement with Assad, partly in hopes of nudging Syria toward peace talks with Israel. He later joined the chorus calling for Assad to step down, saying he had been wrong in his earlier view of the Syrian president as a potential reformer.
On another issue, the United States and other major powers may soon start new talks with Tehran about its nuclear program, hoping to breathe life into thus-far fruitless negotiations aimed at heading off a wider confrontation that could draw in key U.S. ally Israel and wreak havoc on the global economy.
CLOSE TIES TO WHITE HOUSE
Republicans criticized Rice for being more of an Obama ally than a stateswoman. But Kerry, 69, has his own close ties to the Democratic president and little of the personal celebrity wattage that Clinton used to bolster her term in office.
Kerry supported Obama, then a Senate colleague, early in his 2008 presidential campaign and was thought to be a leading contender for his first secretary of state before Obama made the surprise choice of Clinton, his erstwhile rival for the Democratic nomination.
Despite losing out to Clinton, Kerry wan an important Obama ally in the Senate and a strong defender of administration policies on everything from the need to keep funding foreign aid to stepping up sanctions on Iran.
This year, the senior senator from Massachusetts helped the president prepare for his campaign debates with Mitt Romney, standing in for the Republican as Obama practiced for their three head-to-head encounters.
Kerry became chairman of the Senate Foreign Relations Committee in early 2009, replacing Vice President Joe Biden. But he has been a specialist in foreign affairs for years, both boosting and damaging his political career.
The Yale-educated son of foreign service officer Richard John Kerry, he differed from most of well-heeled peers in the 1960s by enlisting in the U.S. Navy and serving two tours of duty during the Vietnam War.
But he broke from - and enraged - the military establishment by becoming a prominent antiwar demonstrator after he returned home, testifying before Congress and even famously throwing away some of his medals.
Foreign policy also helped deal the biggest blow of Kerry's political life - his narrow loss to Republican incumbent Bush in the 2004 presidential election.
Kerry centered his campaign on his opposition to the Iraq war, but Bush's team was able to paint Kerry as a "flip-flopper" for switching policy positions, including his stance on that conflict.
After losing a race for the U.S. House in 1972, Kerry went to Boston College Law School, became a county prosecutor and worked his way up the political ladder before winning his Senate seat in 1984.
He spent his early Senate career in the shadow of his senior Senate counterpart, the late Edward Kennedy. Kerry's background is solidly patrician, like Kennedy's. He can trace his roots back to the first Massachusetts governor, John Winthrop.
He also is one of the Senate's richest members, thanks to his second wife's fortune. Ketchup heiress and philanthropist Teresa Heinz Kerry was the widow of the late Pennsylvania Republican Sen. John Heinz.