Chuck Hagel was forced to make repeated justifications of his positions on Iran, Israel and the Iraq war at a Senate confirmation hearing as Barack Obama's next secretary of defense.

The former senator was accused of holding "extreme views" and endangering US security, in testy exchanges before the armed services committee.

Some of the sharpest exchanges of the lengthy hearing were between Hagel and his old friend Senator John McCain who sought to pin the nominee down over whether he stood by his opposition to the American troop surge in Iraq. Hagel sidestepped the question but was more direct in fending off accusations of being anti-Israel and soft on the Iranian government.

McCain told Hagel that he has "fundamental disagreements" with some of the nominee's positions and that he questioned the "quality of your professional judgement". Several years ago, the two men had a visible falling out over the invasion of Iraq, which Hagel openly questioned.

McCain pressed Hagel to say whether he stood by his opposition to the troop surge in 2007. "Are you going to answer the question, Senator Hagel? The question is whether you were right or wrong," said McCain.

Hagel said he was not going to give a yes or no answer. But McCain came back at him: "I think history has already made a judgement about the surge sir, and you're on the wrong side of it," he said.

Returning to the subject later in the hearing, Hagel talked about his service in Vietnam in 1968, a year in which 16,000 US soldiers died. He said that with that in mind he asked himself before each vote on the Iraq war whether it was worth sending so many soldiers to fight and "in many cases to their deaths".

"I always asked the question: Is it worth the sacrifice?" he said, noting that 1,200 Americans were killed in the surge "Was it necessary? I'm not so sure," he said.

Hagel also noted that the attack on Iraq was at the expense of the war in Afghanistan, the source of the 9/11 attacks.

Iraq was just one line of attack by a string of Republican senators, and some Democrats, who expressed varying degrees of concern over Hagel's positions on a number of issues over the years.

Senator Deb Fischer accused Hagel of "extreme views far to the left even of this administration".

Senator Jim Inhofe said he would not vote to confirm the nominee as secretary of defense. "His record demonstrates what I view as a steadfast opposition to policies that diminish US power and influence throughout the world, as well as a recent trend of policy reversals that seem based on political expediency rather than on core beliefs," he said.

Inhofe, like other senators, zeroed in on Hagel's vote as a senator against labelling the Iranian Revolutionary Guard Corps a terrorist organisation and imposing sanctions against it.

The nominee said he was one of 22 senators who took the same position.He was against the move because the US has "never, ever designated a part of a legitimate government, a state" as a terrorist organisation.

Hagel said the vote would have permitted the US to use force against Iran and America was already in two wars at the time. He noted that John Kerry, the new secretary of state, Joe Biden, now the vice president, also voted against the measure in the Senate.

Hagel was pressed about his opposition to unilateral sanctions against Iran a decade ago, and said that was a different time. He said he regards Iran a state sponsor of terrorism.

Inhofe asked Hagel: "Why do you think the Iranian foreign ministry so strongly supports your nomination for secretary of defense?".

Hagel, exasperated, responded that he had no idea. "I have a difficult time enough with American politics," he said.

Several senators picked up on Hagel's statement in an interview for a book that the "Jewish lobby" intimidates many members of Congress. Hagel later apologised for using "Jewish lobby", saying he should have referred to "pro-Israel lobby".

Senator Roger Wicker pressed Hagel. "Do you stand by your statement they succeed in this town because of intimidation?" he said.

Hagel said he should have described it as influence not intimidation.Senator Lindsey Graham picked up on the issue when he demanded that Hagel name any senator who has been "intimidated by the Israeli lobby" and identify a "dumb thing" Congress has been pressured to do by groups supportive of the Jewish state. "I can't give you an example," said Hagel.

Graham also attacked Hagel for his refusal as a senator several years ago to sign a letter in support of Israel. "The lack of signature by you sends chills up my spine," said Graham.

Hagel repeatedly stated his support for Israel. "I've never voted against Israel, never in the 12 years I was in the Senate," he said.

Later in the hearing Senator Ted Cruz asked about an interview Hagel gave to al-Jazeera in which a caller says Israel is guilty of war crimes. Cruz said Hagel agreed with the viewer and that was "particularly offensive given the Jewish people suffered war crimes" in the Holocaust.

Cruz then accused Hagel of also agreeing with another viewer who described the US as the world's bully.

Hagel also faced repeated questioning over his support for the Global Zero movement which aims to bring about total nuclear disarmament. He was asked if he supported the US unilaterally giving up its nuclear weapons and he said not. "The mainstream thinking of most presidents we've had over the last 65 years ... was reduction of nuclear weapons," said Hagel. © Guardian News and Media 2013