His possible nomination has been rumored for weeks and sparked criticism. Republican lawmakers have already stood in line to voice their opposition to Obama's selection of Hagel, raising questions over whether the former senator would be a strong ally of Israel and be tough enough on Iran.
U.S. House Majority Leader Eric Cantor issued a statement on Monday, calling Hagel "the wrong man for the job at such a pivotal time."
Hagel and Brennan, along with veteran Democratic Senator John Kerry, Obama's nominee for secretary of state announced last month, would form the centerpiece of the president's second-term national security team.
But unlike Kerry who has won bipartisan support, the nominations for Hagel and Brennan could face controversy and even a confirmation fight at the Capitol Hill.
Brennan, a 25-year CIA veteran, withdrew from consideration for the CIA's top position in 2008 amid questions about his alleged connection to harsh interrogation techniques used during the George W. Bush administration.
If confirmed by the Senate, Brennan would succeed retired General David Petraeus, who resigned abruptly days after Obama won the re-election due to a scandal over his extramarital affair with his biographer.
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