WASHINGTON: President Barack Obama's nominee for defense secretary defended himself Thursday against critics from his own Republican Party who have seized on his past statements about Israel, Iran and nuclear weapons that stray from their usual stances.

Chuck Hagel said he cannot be defined by a single vote or quote and insisted that his worldview hasn't changed. He said the U.S. must maintain the strongest military in the world and lead internationally.

His 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 is 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 comments about the influence of a "Jewish lobby" and his view of gay rights and past description of a diplomatic nominee as "openly, aggressively gay." In the past, Hagel has questioned the efficacy of unilateral sanctions on Iran, arguing that penalties in conjunction with international partners made more sense.

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.

But a number of political action groups continue to attack Hagel on those issues and discourage the approval of his nomination.

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. Sen. Jim Inhofe, the top Republican lawmaker on the committee, has said he and Hagel are "too philosophically opposed."

Crucial for Hagel is the questioning by Republican Sen. John McCain. Hagel and McCain are fellow Vietnam veterans who once had a close relationship during their years in the Senate, but politics and Hagel's opposition to increased troop numbers in Iraq divided the two men.

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. Sen. Lindsey Graham earlier this month described Obama's selection as an "in-your-face" pick but was a bit less critical this week.

"Who are we getting - the guy today or the guy who said things before?" Graham said Tuesday after a 20-minute meeting with Hagel. Graham said he doesn't doubt Hagel's "personal integrity, but I do have real concerns about his policy positions."

Hagel addressed several of the issues in a 112-page questionnaire to the committee in which he said his wartime experience would shape his decisions about using military force.

"I understand what it is like to be a soldier in war," wrote Hagel. "I also understand what happens when there is poor morale and discipline among the troops and a lack of clear objectives, intelligence and command and control from Washington. I believe that experience will help me as secretary of defense to ensure we maintain the best fighting force in the world, protect our men and women in uniform and ensure that we are cautious and certain when contemplating the use of force."

In his responses, 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.

Questioned about all options, Hagel said, "If confirmed, I will focus intently on ensuring that the U.S. military is in fact prepared for any contingency."

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. "He drives hard. He's someone who searches for the right approach and the right policy."