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A member of the Senate committee that Chuck Hagel would have to clear if he's nominated for defense secretary told Fox News in an exclusive interview Thursday that she has "serious" reservations about the former senator's past positions.

The comments from Sen. Kelly Ayotte, R-N.H., a member of the Armed Services Committee, followed concerns expressed by other lawmakers about Hagel's stands on Israel, Cuba and other hot foreign policy topics. Hagel, a Republican who served two terms as senator from Nebraska, is considered a leading contender for the top Pentagon post.

"I do have serious concerns about his positions that he's stated on Israel, some of the statements he has made in the past, as well as his positions on Iran," Ayotte said in a brief interview on Capitol Hill. "If he is nominated and comes before the Senate Armed Services Committee, I plan to vigorously question him on his prior statements, and those positions, in particular."

The White House, fearing a replay of the fiasco in which U.N. Ambassador Susan Rice, ensnared in the Benghazi controversy, was forced to withdraw her name from consideration as a potential secretary of state, has quietly mounted a pre-emptive defense of Hagel. The effort has included lining up eminent supporters and reminding Americans of Hagel's infantry service in Vietnam.

"Senator Hagel has been a remarkable servant to this country, a recipient of two Purple Hearts," said White House Press Secretary Jay Carney in a briefing with reporters on Thursday. "He fought for this country and -- and has served this country admirably in a number of capacities."

Daniel C. Kurtzer, the former U.S. ambassador to Israel during George W. Bush's first term as president, also weighed in.  "(Hagel) has been, over the course of a long career in public service, a supporter of the State of Israel and its security requirements," Kurtzer told Fox News. "He has spoken out very forcefully about this and he has written about it in his book."

But a number of Jewish groups and influential editorial page writers have questioned Hagel's fitness for the job. The Washington Post said this week that Hagel's positions - including his opposition to the imposition of sanctions on Iran - are out of "the mainstream," and place him to the left of the president himself.  And the Anti-Defamation League has said that Hagel's statement in 2006 that "the Jewish lobby intimidates a lot of people" on Capitol Hill bordered on anti-Semitism.

"That comment is inappropriate," Sen. John McCain, R-Ariz., told The Associated Press. "There's no such thing as a Jewish lobby. There's an Armenian lobby, there's not a Jewish lobby. There's an Israeli lobby. It's called AIPAC, very influential."

Asked if she thinks Hagel's problems extend beyond the Republican side of the aisle, Ayotte said yes. "Given some of the prior statements he has made with regard to Israel ... other positions he has taken, on Iran sanctions, I would think members of both parties would want to ask very important questions about those positions and whether he still holds them and why he made those statements," she said.

Hagel has favored direct talks with Iran, and criticized considerations of a military strike against the Islamic regime's nuclear facilities by either the United States or Israel.

Opponents have pointed to Hagel's votes against sanctions on Iran and circulated letters that Hagel signed -- and ones he declined to sign -- many of which had been pressed by the American Israel Public Affairs Committee, the powerful pro-Israel lobby. In August 2006, for example, Hagel refused to sign a letter urging the European Union to declare Hezbollah a terrorist organization, making him one of only twelve senators who balked.

In 2007, Hagel sent a letter to President Bush urging talks with Iran.  He may also come under scrutiny for his past opposition to the trade embargo against Cuba. A spokesman for Sen. Marco Rubio, R-Fla., a Cuban-American lawmaker, signaled the issue could prompt Rubio to seek to block the nomination if Hagel is tapped for the Pentagon post.

"Promoting democracy in Latin America is a priority for Sen. Rubio, and he's put holds on other Administration nominees over the issue. If President Obama were to nominate Sen. Hagel for a cabinet position, I'm sure we would have questions about Cuba positions," Rubio spokesman Alex Conant said in a statement.

Conant added that "we don't prejudge the nominations." The White House said no decisions about the defense secretary position have yet been made.

The Associated Press contributed to this report.