WASHINGTON (Reuters) - President Barack Obama on Monday will announce the nominations of Republican Chuck Hagel as his next defense secretary and White House counterterrorism adviser John Brennan as the new CIA director, a senior administration official said.

The choice of Hagel, a maverick former Republican senator and decorated Vietnam veteran, had been widely tipped to replace Leon Panetta at the Pentagon. The move will likely set up a tough Senate confirmation battle against critics who have attacked his record on Israel and Iran.

Brennan, who formerly served at the CIA, will succeed retired general David Petraeus, who resigned amid a scandal over an extramarital affair with his biographer.

(Reporting By Matt Spetalnick; Editing by Jon Boyle)