Chuck Hagel, GOP Senators Butt Heads at Defense Secretary Confirmation Hearing

"When I voted against some of those unilateral sanctions on Iran, it was a different time," Hagel said, referring to votes in the early 2000s. "We were in a different place with Iran at that time. As a matter of fact, the Bush administration did not want a five-year renewal of [the Iran and Libya Sanctions Act] at that time because they weren't sure of the effectiveness of the sanctions."

Hagel said his record of public statements shows he has consistently referred to Hamas and Hezbollah as terrorist groups and Iran as a state sponsor of terrorism.

McCain Pushes Hagel: 'You Were on the Wrong Side of History' Watch Video

Graham Says Hagel 'Sends Chills Up My Spine' Watch Video

Obama Announces Chuck Hagel for Secretary of Defense Watch Video

"The way I approached every vote I took in the Senate was what I thought would be the most effective," Hagel said, defending his vote against labeling Iran's guard corps as a terrorist group. "What was the situation at the time, how can we do this smarter and better?"

Sen. James Inhofe, R-Okla., the committee's top Republican, said he will oppose Hagel's nomination.

"Senator Hagel is a good man who has a record of service," Inhofe said of his former GOP colleague, while concluding, "He is the wrong person to lead the Pentagon.

Hagel was introduced at the hearing by former Sens. Sam Nunn, D-Ga., and John Warner, R-Va., two respected former members of the Armed Services Committee, both of whom lavished praise on Obama's nominee.