WASHINGTON (Reuters) - President Barack Obama on Friday will announce the nomination of Senator John Kerry as secretary of state to succeed Hillary Clinton, marking his first major step in the overhaul of his national security team on the cusp of his second term.

Kerry, chairman of the Senate Foreign Relations Committee and the Democratic presidential candidate in 2004, had been widely tipped to become America's top diplomat after U.N. Ambassador Susan Rice withdrew her name from consideration last week. The Massachusetts Democrat is expected to win easy confirmation from his Senate colleagues.

Obama will announce Kerry's nomination on at 1:30 p.m. on Friday but will withhold any decision on a new defense secretary, senior administration officials said. The president faces a growing backlash from critics of former Republican Senator Chuck Hagel, considered a leading candidate to replace Leon Panetta at the Pentagon.

Kerry, a stalwart Obama supporter known to have long coveted the secretary of state post, will take over from Clinton who has been consistently rated as the most popular member of the president's cabinet.

But he will also have to pick up the pieces after a scathing official inquiry found serious security lapses by the State Department in the deadly September 11 attack on the U.S. consulate in Benghazi, Libya - a report that has tarnished the final days of Clinton's tenure.

Kerry's nomination follows a political firestorm that engulfed Rice, seen as the early favorite for the State job, spearheaded by Republicans highly critical of her role in the administration's early explanations for the Benghazi assault.

Rice, defended by Obama and other senior members of the administration, said last Thursday she was withdrawing her name from consideration to avoid a potentially lengthy and disruptive confirmation process in the U.S. Senate.

Kerry, known nationally through his presidential run and for his role as a Democratic power broker in the Senate, offers no such challenges.

After losing narrowly to Republican George W. Bush in the 2004 presidential election, Kerry forged a new identity as a congressional leader on foreign policy, often serving as a low-profile emissary for the White House.

Kerry's departure from the Senate forces Democrats to defend his seat. The just-defeated but still-popular Massachusetts Republican Senator Scott Brown, who took office in early 2010 after winning the last special election for a Massachusetts seat, is widely expected to run for Kerry's seat.