(Reuters) - President Barack Obama on Friday nominated John Kerry to replace Hillary Clinton as secretary of state, calling the veteran U.S. senator the "perfect choice" for America's top diplomat as he began reshaping his national security team for his second term.

Obama settled on Kerry, chairman of the Senate Foreign Relations Committee and the 2004 Democratic presidential candidate, after the frontrunner, U.N. Ambassador Susan Rice, withdrew from consideration last week.

Even as Obama put one important piece of his revamped Cabinet in place, he held off on naming a new defense secretary. The delay came in the face of a growing backlash from critics of former Republican Senator Chuck Hagel, who is considered a leading candidate to replace Leon Panetta at the Pentagon.

With Kerry standing at his side, Obama expressed confidence that the senator - a stalwart supporter who has long coveted the State Department job - would win swift confirmation from his Senate colleagues.

"As we turn the page on a decade of war, he understands that we've got to harness all elements of American power and ensure that they're working together.," Obama said. "John's earned the respect and confidence of leaders around the world. He is not going to need a lot of on-the-job training."

The announcement fell short of the White House's earlier hopes of rolling out national security appointments, including a new CIA director, all at once before Christmas. That ambition was thwarted both by the Hagel controversy as well as other matters that have occupied Obama's attention - the standoff over the "fiscal cliff" and last week's Newtown gun massacre.

Kerry, 69, will take over take over from Clinton, who has been consistently rated as the most popular member of the president's cabinet.

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