WASHINGTON -- President Barack Obama's pick of Chuck Hagel to run the Pentagon faces rough going in the Senate as a handful of Republicans quickly announced their opposition to a former GOP colleague, and several skeptical Democrats reserved judgment until the nominee explains his views on Israel and Iran.

The concerns about Hagel complicate his path to Senate confirmation but are not necessarily calamitous as the White House pushes for the first Vietnam War veteran to oversee a military emerging from two wars and staring at deep budget cuts.

Obama also tapped White House counterterrorism adviser John Brennan to head the CIA. Brennan, a 25-year CIA veteran, faces no major obstacles, but he is expected to be hit with questions about torture and administration leaks of secret information.

Moments after Obama announced his selection of Hagel and called him "the leader that our troops deserve," some Senate Republicans voiced opposition to the former Nebraska lawmaker who spent 12 years in the Senate.

"Given Chuck Hagel's statements and actions on a nuclear Iran, Hamas and Hezbollah, I think his confirmation would send exactly the wrong message to our allies and enemies alike," Sen. David Vitter, R-La., said in a statement. "Israel, our strongest ally in the region, is dealing with a lot of threat and uncertainty right now; Hagel would make that even worse."

Other Senate Republicans, including the No. 2 GOP lawmaker, John Cornyn of Texas, new member Ted Cruz of Texas and Mississippi's Roger Wicker, signaled they would vote against the nomination.

Hagel has upset some Israel backers with his comment about the "Jewish lobby," his votes against unilateral sanctions against Iran while backing international penalties on the regime in Tehran and his criticism of talk of a military strike by either the U.S. or Israel against Iran.

He also upset gay rights groups over past comments, including his opposition in 1998 to President Bill Clinton's choice of James Hormel as ambassador to Luxembourg. He referred to Hormel as "openly, aggressively gay." Hagel recently apologized, saying his comments were "insensitive."

Those remarks and actions have created fierce opposition from some pro-Israel groups, criticism from some Republicans and unease among some congressional Democrats.

The Log Cabin Republicans took out a full-page ad in The Washington Post highlighting their opposition to Hagel, and Gregory T. Angelo, interim executive director of the gay rights group, said the gay and lesbian grassroots organization is considering other steps in a campaign against Hagel's nomination.

House Majority Leader Eric Cantor, R-Va., who does not have a vote on the nomination, called Hagel the "wrong man" for the job and complained that "his inflammatory statements about Israel are well outside the mainstream."

In an interview with the Lincoln (Neb.) Journal Star, Hagel said his statements have been distorted and there is "not one shred of evidence that I'm anti-Israeli, not one (Senate) vote that matters that hurt Israel."

In a critical sign of support for Hagel's prospects, the 66-year-old moderate Republican attracted words of praise from Senate Majority Leader Harry Reid, D-Nev., Senate Armed Services Committee Chairman Carl Levin, D-Mich., and Sen. Dianne Feinstein, D-Calif., who heads the Intelligence panel.

Levin called Hagel "well-qualified." Feinstein described him as "a knowledgeable and independent voice with a strong grasp of the pressing national security issues facing our country." Reid said "few nominees have such a combination of strategic and personal knowledge of our national defense needs."

Sen. Patrick Leahy, D-Vt., said Hagel "is a combat veteran who still carries shrapnel in his body from his wounds. He will not need on-the-job training."

Several Democrats, most notably Sen. Chuck Schumer of New York, and a number of Republicans, including Jim Inhofe of Oklahoma and John McCain of Arizona, said they would await the Senate process and the opportunity to question Hagel. That raises the stakes for his private meetings with senators and his confirmation hearing in the next few weeks before the Armed Services Committee.

While some opposition was expected for Obama's nominee, no senator has threatened to block the selection. Republican and Democratic congressional aides said the White House wouldn't have put forth the nomination if it didn't think it had the votes for Hagel's confirmation. Democrats hold a 55-45 advantage in the Senate.

Former Sen. Max Cleland, D-Ga., himself a wounded Vietnam veteran, said he thinks Hagel "has to clarify" his positions on issues like Iran and Israel.

But Cleland also said in an interview on "CBS This Morning" Tuesday that Hagel is battle-tested and ready for the challenges of a confirmation process, accusing the Nebraskan's critics of "swatting at nothing, shadow-boxing."

Hagel's hopes rest on the willingness of senators to give a president his picks for the Cabinet, and the high threshold of deeming a nominee unfit for a civilian appointment. Politically, it would be remarkable for the Democratic-controlled Senate to deny Obama his nominee and undercut the president at the start of his second term and in the midst of fierce budget negotiations with Republicans.

The Senate has rejected one of its own in recent years.

In 1989, the Democratic-led Senate voted down the nomination of John Tower to serve as defense secretary over questions about the former Republican senator's personal life. It was an embarrassment to President George H.W. Bush, who then turned to Dick Cheney to lead the Pentagon.

While the Armed Services Committee decides Hagel's fate, the Senate Intelligence panel will decide on Brennan, 57, a close Obama adviser for the past four years.

Brennan withdrew from consideration for the spy agency's top job in 2008 amid questions about his connection to harsh interrogation techniques used during the George W. Bush administration. He is certain to face questions about the issue again from Democrats while Republicans press him on leaks of classified information in the Obama administration.

In announcing the nominations in the East Room, Obama urged the Senate to move quickly.

"When it comes to national security, we don't like to leave a lot of gaps between the time that one set of leaders transitions out and another transitions in," the president said.