© Dave Kaup / Reuters
The White House informed the Hagel camp over the weekend that Obama intends to announce the nomination at the White House on Monday.
The two people with knowledge of the process, who spoke on the condition of anonymity because they were not authorized to speak about the nomination before Obama does, said key members of Congress were being being notified Sunday afternoon about the decision.
Hagel would add a well-known Republican to the president's second-term Cabinet at a time when Obama, after a bitter presidential campaign, is looking to better bridge the partisan divide.
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 that Hagel's record would be given a fair shake in the Senate if he is 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 probably 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.
Concerning the opposition that has arisen on the Hill before Hagel's formal nomination, a senior administration official said Sunday that the White House expects Democrats to support the choice, as well as many Republicans who served with Hagel.
"Having a name floated and having one officially put forward are two different things," the official said.
Hagel, who twice received the Purple Heart for wounds suffered in Vietnam, served in the U.S. 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 war after he initially supported the invasion.
"A lot of Republican opposition is rooted in the fact that he left his party on Iraq," the senior administration official said. "And we think it will be very hard for Republicans to stand up and be able to say that they oppose someone who was against a war that most Americans think was a horrible idea."
Hagel also has been a strong advocate for veterans, an issue Obama has spoken about frequently as tens of thousands of U.S. troops return from battlefields after more than a decade of war. The administration official said Hagel, as a result, is "uniquely qualified" to help wind down the Afghan war in the next two years and make budget decisions to support the returning troops.
Some of the recent criticism directed at Hagel has focused on his mixed record regarding the imposition of sanctions on Iran. During his time in the Senate, Hagel opposed several bills to impose sanctions against Iran unilaterally. But he also supported measures to do so as part of multinational efforts, and he endorsed labeling Iran a state sponsor of terror.
His record has raised concern among some of Israel's supporters in the United States, who 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 $40 billion in military aid to Israel over his tenure.
Obama, who worked with Hagel on nuclear non-proliferation issues and other foreign policy matters in the U.S. 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 the Islamic Republic 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 co-chairman 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, telling writer Aaron David Miller that "the Jewish lobby intimidates a lot of people up here."
"If Hagel is nominated, it is very difficult to imagine a circumstance in which I could support his nomination," Sen. Ted Cruz (R-Tex.) said on "Fox News Sunday."
But Hagel has many supporters, including former ambassadors, senators and secretaries of state who value his experience and independence.
A network of his supporters has rallied in recent weeks to offer a defense of Hagel's record as the criticism has grown, and say privately that they expect him to receive strong public defense from many Republicans and Democrats alike once the nomination is official.
Writing last week in the Wall Street Journal, Ryan Crocker, the former U.S. ambassador in Iraq and Afghanistan, called Hagel "a statesman," adding that "America has few of them."
Hagel, 66, would be taking over the Pentagon at a time of budget cuts and a changing mission after two long wars. Defense Secretary Leon Panetta is retiring to his home in California.
If confirmed, Hagel would join Transportation Secretary Ray LaHood as the second Republican in Obama's Cabinet.
I see they are not letting up on trying to create the illusion that the obama admin are 'at odds' with israel.