But Hagel's expected nomination has drawn sharp criticism in recent weeks, particularly from Republicans who have questioned his commitment to Israel's security.
The choice sets up a nomination fight Obama appeared unwilling to have over his preferred pick for secretary of state, Susan Rice, who pulled out of consideration for that job last month amid Republican complaints over her role in explaining the attacks in Benghazi, Libya, last year that killed Ambassador J. Christopher Stevens and three other Americans.
In an appearance Sunday on CNN's State of the Union, Sen. Lindsey Graham (R., S.C.) called Hagel's selection "an in-your-face nomination."
But Senate Minority Leader Mitch McConnell (R., Ky.) said Hagel's record would be given a fair shake in the Senate if he was nominated. McConnell stopped short of saying whether he was prepared to support or oppose his former colleague.
"He's certainly been outspoken in foreign policy and defense over the years," McConnell said on ABC's This Week With George Stephanopoulos. "The question we'll be answering if he's the nominee is do his views make sense for that particular job? I think he ought to be given a fair hearing, like any other nominee. And he will be."
The Hagel announcement will begin what White House officials have said will likely be a busy week of announcements regarding who will fill out Obama's second-term cabinet and senior staff.
The president returned from a curtailed holiday in Hawaii on Sunday and will begin making a series of final personnel decisions delayed by the year-end negotiations with Congress over taxes and spending cuts in the next few days.
Hagel, who twice received the Purple Heart for wounds in Vietnam, served in the Senate for two terms, ending in 2009.
He was an outspoken and often independent voice as a member of the Senate Foreign Relations Committee, breaking with many in his party to sharply criticize the management of the Iraq was after he initially supported the invasion. Hagel also has been a strong advocate for veterans.
Much of the recent criticism over Hagel's record has focused on his past opposition to imposing sanctions on Iran, against which he voted three times as a senator. He also supported labeling Iran a state sponsor of terrorism.
His record has raised concern among some of Israel's supporters in the United States, who say they fear Hagel may not be sufficiently committed to Israel's security.
But his defenders point to his record as a senior senator on the Foreign Relations Committee, where he voted for nearly $38 billion in military aid to Israel over his tenure.
Obama, who worked with Hagel on nuclear nonproliferation and other foreign policy matters in the Senate, has vowed to prevent Iran from using its uranium-enrichment program to develop a nuclear weapon.
Obama has tightened international sanctions during his term to pressure Iran to give up the effort, of which Hagel has spoken in support of in recent comments. The Iranian government has said it is pursuing nuclear power, not weapons.
Since leaving office, Hagel has served as cochairman of Obama's intelligence advisory board.
Hagel has advised the president to open talks with Hamas, the armed Palestinian movement that does not recognize Israel's right to exist. He also has complained about the influence that Israel's supporters exert on members of Congress.
"If Hagel is nominated, it is very difficult to imagine a circumstance in which I could support his nomination," Sen. Ted Cruz (R., Texas) said on Fox News Sunday.
But Hagel has many supporters, as well, including former ambassadors, senators, and secretaries of state who value his experience and independence.
Hagel, 66, would take over the Pentagon at a time of budget cuts and a changing mission after two long wars from Leon Panetta, who is retiring to his home in California. If confirmed, he would join Transportation Secretary Ray LaHood as the second Republican in Obama's cabinet.