WASHINGTON -- A deeply divided Senate voted on Tuesday to confirm Republican Chuck Hagel to be the next U.S. defence secretary, handing President Barack Obama's pick the top Pentagon job just days before billions of dollars in automatic, across-the-board budget cuts hit the military.

The vote was 58-41, with four Republicans joining the Democrats in backing the contentious choice.

Republicans had opposed their onetime colleague, casting him as unqualified for the job, hostile toward Israel and soft on Iran. They described him as a radical and far out of the mainstream.

The vote came just hours after Republicans dropped their unprecedented delay of a Pentagon choice and allowed the nomination to move forward on a 71-27 vote.

Hagel, 66, a former 12-year senator and twice-wounded Vietnam combat veteran, succeeds Defence Secretary Leon Panetta. Hagel is expected to be sworn in at the Pentagon on Wednesday.

Obama welcomed the bipartisan Senate vote, although 41 Republicans opposed his nominee, and said in a statement that "we will have the defence secretary our nation needs and the leader our troops deserve."

He looked past the divisions and said he was grateful to Hagel "for reminding us that when it comes to our national defence, we are not Democrats or Republicans, we are Americans, and our greatest responsibility is the security of the American people."

Republican objections remained strong well after the vote.

"I continue to have serious questions about whether Chuck Hagel is up to the job of being our secretary of defence," Sen. Lindsey Graham, a Republican, said in a statement. "I hope, for the sake of our own national security, he exceeds expectations."

Hagel joins Obama's retooled second-term, national security team of Secretary of State John Kerry and CIA Director-designate John Brennan at a time of uncertainty for a military emerging from two wars and fighting worldwide terrorism with smaller, deficit-driven budgets.

Among his daunting challenges are deciding on troop levels in Afghanistan as the United States winds down its combat presence and dealing with $46 billion in budget cuts set to kick in on Friday. He also will have to work with lawmakers who spent weeks vilifying him.

Republicans insisted that Hagel was battered and bloodied after their repeated attacks during the protracted political fight.

"He will take office with the weakest support of any defence secretary in modern history, which will make him less effective on his job," said Sen. John Cornyn of Texas, the Senate's No. 2 Republican.

Not so, said Democratic Sen. Jack Reed, who pointed out that Hagel now has the title and the fight is history.

"All have to work together for the interest of the country," said Reed.

The vote ended one of the most bitter fights over a Cabinet choice and former senator since 1989 when the Democratic-led Senate defeated newly elected President George H.W. Bush's nomination of Republican John Tower to be defence secretary.

In the course of the rancorous, seven-week nomination fight, Republicans, led by freshman Sen. Ted Cruz and Sen. Jim Inhofe, insinuated that Hagel has a cozy relationship with Iran and received payments for speeches from extreme or radical groups. Those comments drew a rebuke from Democrats and some Republicans.

Sen. Carl Levin, a Democrat and the chairman of the Armed Services Committee, dismissed the "unfair innuendoes" against Hagel and called him an "outstanding American patriot" whose background as an enlisted soldier would send a positive message to the nation's servicemen and women.

Sen. Claire McCaskill, a Democrat, questioned how the confirmation process devolved into a character assassination in which Hagel was accused of "having secret ties with our enemies."

"I sincerely hope that the practice of challenging nominations with innuendo and inference, rather than facts and figures, was an aberration and not a roadmap," she said in a statement after the vote.

Sen. John McCain, a Republican, clashed with his onetime friend over his opposition to President George W. Bush's decision to send an extra 30,000 troops to Iraq in 2007 at a point when the war seemed in danger of being lost. Hagel, who voted to authorize military force in Iraq, later opposed the conflict, comparing it to Vietnam and arguing that it shifted the focus from Afghanistan.

McCain said several Republican lawmakers also had "a lot of ill will" toward the moderate Republican for his criticism of Bush and his backing for Democratic candidates. McCain voted against Hagel.

Republicans also challenged Hagel about a May 2012 study that he co-authored for the advocacy group Global Zero, which called for an 80 per cent reduction of U.S. nuclear weapons and the eventual elimination of all the world's nuclear arms.

In an echo of the 2012 presidential campaign, Hagel faced an onslaught of criticism by well-funded, Republican-leaning outside groups that labeled the former senator "anti-Israel" and pressured senators to oppose the nomination. The groups ran television and print ads criticizing Hagel.

Opponents were particularly incensed by Hagel's use of the term "Jewish lobby" to refer to pro-Israel groups. He apologized, saying he should have used another term and should not have said those groups have intimidated members of the Senate into favouring actions contrary to U.S. interests.

Hagel's nomination also became entangled in Republican demands for more information about the deadly assault on the U.S. diplomatic mission in Benghazi, Libya, last September. Ambassador Chris Stevens and three other Americans were killed in that attack.

Republicans allowed the nomination to move forward, with 18 Republicans joining the Democrats. Many had warned against the precedent of denying a president his Cabinet choices.