WASHINGTON — President Obama is expected to nominate Chuck Hagel, a former Republican senator and Vietnam veteran, to be secretary of Defense, officials said, setting up a confirmation battle with lawmakers and interest groups critical of his views on Israel and Iran.

White House officials said Friday afternoon that the president hadn’t formally offered the job to Hagel, but others familiar with the process said that the announcement could come as soon as Monday

By nominating a Republican to run the Defene Department, Obama gives his second-term national security team a bipartisan cast at a time when the White House is rapidly winding down the war in Afghanistan and planning for even deeper cuts in the defense budget.