President Barack Obama will nominate Chuck Hagel as his next defense secretary, a senior administration official said Sunday, Jan 6 choosing a former Senate colleague and a decorated Vietnam veteran and signaling he's ready for a contentious confirmation fight likely dominated by questions about Hagel's stands on Israel and Iran, The Associated Press reported.

Obama, who avoided a Capitol Hill battle by deciding not to nominate U.N. Ambassador Susan Rice as his first choice for secretary of state, went ahead with Hagel, 66, even as leading Republicans announced their opposition though they stopped short of saying they might try to block Hagel.

Seeking to soften the ground, the White House was alerting Senate Democrats that Hagel's selection as the successor to Defense Secretary Leon Panetta in Obama's second-term Cabinet was imminent, according to a congressional official.

Obama, who returned to Washington on Sunday from his Hawaiian vacation, was expected to nominate Hagel on Monday. Congress is on break this coming week.

The officials requested anonymity in order to discuss Hagel's nomination ahead of Obama.

Hagel, a moderate Republican, built a strong relationship with Obama during their travel as senators. But the former Nebraska lawmaker has faced withering criticism from Congress since emerging as the front-runner for the Pentagon post.