Video: Sen. John McCain and Chuck Hagel tangle over Iraq

President Barack Obama's nominee for defense secretary said Thursday he would not hesitate to use the "full force of the U.S. military" as he plunged into a Senate confirmation fight with critics from his own Republican Party, who worry that his past statements about Israel, Iran and nuclear weapons are signs of weakness.

Chuck Hagel's appearance at a Senate Armed Services Committee hearing could be crucial in determining whether he will win Senate confirmation to succeed Defense Secretary Leon Panetta in Obama's second-term national security team.

The hearing was the first time the former senator has publicly addressed the barrage of criticism that he is not sufficiently pro-Israel or tough enough on Iran. His past comments about the influence of a "Jewish lobby" and his description of a diplomatic nominee as "openly, aggressively gay" have been scrutinized. Hagel also has questioned the efficacy of unilateral sanctions on Iran, arguing that penalties in conjunction with international partners made more sense.

Hagel's record "is deeply troubling and out of mainstream views," Sen. Jim Inhofe, the top Republican on the committee, said shortly after the hearing began. Republican Sen. John McCain had even sharper words for Hagel during a spirited exchange over the war in Iraq.

Crucial for Hagel was Thursday's feisty questioning by McCain. Hagel and McCain are fellow Vietnam veterans who once had a close relationship during their years in the Senate, but Hagel's evolving opposition to the Iraq war caused a split between the two men that was on full display.

McCain pressed Hagel on whether he was right or wrong about his opposition to the influx of 30,000 U.S. troops in Iraq in 2007. 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.

"Were you right? Were you correct in your assessment?" McCain asked.

"I would defer to the judgment of history to sort that out," Hagel said as the two men talked over each other.

McCain has praised Hagel's military service but said he had serious concerns about positions the nominee has taken on various issues. He said he is reserving judgment until after the hearing.

Hagel has been meeting one-on-one with senators, winning support from influential Jewish Sen. Charles Schumer, and he has taken a harder line on Iran. Hagel also has insisted that he will implement the military's policy allowing gays to serve openly and move ahead on opening combat roles to women.

Hagel would be the lone Republican in Obama's Cabinet if the Senate confirms him, but the prospect has failed to placate Republican senators in a post-election atmosphere that remains politically divisive.

Once the hearing was under way, the Republican National Committee put out a news release titled "Chuck Hagel is the Wrong Choice for Secretary of Defense," contending that he would weaken the nation's military.

Hagel said he was committed to Obama's goal of ensuring that Iran does not obtain a nuclear weapon, and he insisted that all options, including military force, are on the table.

"My policy is one of prevention, and not one of containment — and the president has made clear that is the policy of our government," Hagel said.

Hagel said he always supported multilateral sanctions against Iran. He also expressed support for maintaining a strong, modern nuclear arsenal, a position that has been challenged because of his support for the Global Zero organization's recommendation of nuclear cuts.

"We are not going to unilaterally disarm," Hagel said.

Hagel added that America "must engage — not retreat — in the world," and he insisted that his record is consistent on that point.

If confirmed, Hagel, a decorated Vietnam combat veteran, would be the first enlisted man and first Vietnam veteran to serve as defense secretary.

Six Republicans, including four members of the Armed Services panel, have said they will oppose Hagel's nomination.

In responses to a questionnaire before the hearing, Hagel adopted a hard line on Iran and its possible pursuit of a nuclear weapon. He echoed Obama's view that all options are feasible to stop Tehran, praised the rounds of penalties and warned of "severe and growing consequences" if Iran balks at international demands.

He said that he would continue to put in place the "smart, unprecedented and effective sanctions against the Iranian regime" that Congress and the Obama administration have adopted in recent years.

The criticism of Hagel has surprised some of Hagel's strongest backers.

"This idea that's being propagated that he might be soft on adversaries. Chuck Hagel's not soft on anybody, particularly himself," said Democratic Sen. Jack Reed, a member of the Armed Services Committee, in a conference call with Hagel allies.

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Associated Press writer Donna Cassata contributed.

Copyright 2013 The Associated Press.