Reports Sunday said the White House had notified lawmakers to expect Hagel’s formal nomination as early as Monday.
Hagel’s selection will likely face fierce opposition in the Senate.
Pro-Israel groups have questioned his support for the U.S. ally after a remark he made in office accused the “Jewish lobby” of intimidating fellow lawmakers. Pro-gay rights groups have also hammered Hagel over critical remarks he made toward an openly gay ambassadorial nominee.
Hagel apologized for those comments last month and Obama also publicly defended the former senator.
In an interview last week, the president said he had not made a decision about who would replace current Secretary of State Leon Panetta at the Pentagon, but said nothing in Hagel’s public record disqualified him from serving in that post.
Sen. Lindsey Graham (R-S.C.) on Sunday said Hagel could expect a tough hearing and called the likely selection an “in your face nomination” from Obama.
Graham said Hagel would be the “most antagonistic secretary of Defense toward the state of Israel in our nation’s history.”