WASHINGTON – Susan Rice, the embattled U.N. ambassador, abruptly withdrew from consideration to be the next secretary of state Thursday after a bitter, weekslong standoff with Republican senators who declared they would vigorously fight her nomination.

The reluctant announcement makes Massachusetts Sen. John Kerry the likely choice to be the nation’s next top diplomat when Hillary Rodham Clinton departs soon. Support for the possible choice of Rice had been waning.

In another major part of the upcoming Cabinet shake-up for President Barack Obama’s second term, former Republican Sen. Chuck Hagel of Nebraska now is seen as the front-runner to be defense secretary, with official word coming as soon as next week.