* Iran, Iraq, defense budget cuts top concerns of panel
* McCain presses Hagel on past opposition to troop surges
* "Tough day for Chuck Hagel"
* Support from Democrats (Adds analysts' comments, details)
By Phil Stewart and Patricia Zengerle
WASHINGTON, Jan 31 (Reuters) - Republican lawmakers attacked Chuck Hagel on Thursday at a contentious hearing over his nomination to become the next U.S. defense secretary, questioning his judgment on war strategy and putting him broadly on the defensive.
In one of the most heated exchanges, Senator John McCain aggressively questioned Hagel, interrupting him and talking over him at times. He voiced frustration at the former Republican senator's failure to say plainly whether he was right or wrong to oppose the 2007 "surge" of U.S. troops in Iraq.
"Your refusal to answer whether you were right or wrong about it is going to have an impact on my judgment as to whether to vote for your confirmation or not," McCain said.
Hagel, who like McCain is a decorated Vietnam War veteran, declined to offer a simple yes or no answer, responding, "I would defer to the judgment of history to sort that out."
As President Barack Obama's choice to lead the Pentagon in his second term, Hagel could clinch Senate approval thanks to help from majority Democrats. But he appeared to pick up little new Republican support as his hours-long hearing wore on.
Although Republicans could create procedural hurdles to block him, there were no overt promises at the hearing to do so.
"Unless the Republicans filibuster him, the nomination is going to go through," said Bill Galston, a former adviser to President Bill Clinton.
Ford O'Connell, a Republican strategist, said, "It's been a tough day for Chuck Hagel overall."
"I think the Republicans are trying to decide whether they really want to push the pedal to the floor with Hagel," he said.
The Senate Armed Services Committee's Democratic chairman, Carl Levin, praised Hagel's performance after the nearly eight-hour hearing ended. "I thought he did very well. I thought he was responsive. He kept his cool. His experience was both modestly and eloquently described," the Michigan senator said.
The earliest the committee will vote on Hagel's nomination is next Thursday, Levin added.
Hagel's fellow Republicans dredged up a series of his past controversial statements on Iran, Israel and U.S. nuclear strategy, trying to paint him as outside mainstream security thinking. Even in polarized Washington, the grilling was highly unusual for a Cabinet nominee.
Senator Lindsey Graham of South Carolina laid into Hagel for once accusing a "Jewish lobby" of intimidating people in Washington, comments Hagel repeatedly said he regretted. Asked whether he could name one lawmaker who had been intimidated, Hagel said he could not. It was one of the many times he appeared uncomfortable.
"I can't think of a more provocative thing to say about the relationship between the United States and Israel and the Senate or the Congress than what you said," Graham said.
SEEKING TO SET RECORD STRAIGHT
If he is ultimately confirmed, Hagel will take over the Pentagon at a time of sharp reductions in defense spending, and with the United States still facing major challenges, including China, Iran and North Korea.
Hagel, speaking publicly for the first time since the attacks against his nomination began, seemed cautious and halting at times. He sought to set the record straight, assuring the panel that he backed U.S. policies of preventing Iran from obtaining a nuclear weapon and supporting a strong Israel.
"No one individual vote, no one individual quote, no one individual statement defines me, my beliefs, or my record," Hagel said in opening remarks to the packed hearing room.
"My overall world view has never changed: that America has and must maintain the strongest military in the world."
In an unusual reversal of partisanship, Democrats, more than Republicans, gave Hagel sympathetic support and time to air his views, which adhered broadly to Pentagon policy.
"I feel like I want to apologize for some of the tone and demeanor from today," said Senator Joe Manchin, a Democrat from West Virginia.
Galston said Thursday's hearing appeared to sap some of the momentum Hagel had going into the session after weeks of pushback by his allies against criticism.
He added, "It's going to be harder to present Hagel's confirmation now as a victory for bipartisanship - overcoming doubts, or coming together around sensible mainstream policies."
Despite the harsh tone from many Republicans, some senators from the party approached Hagel more collegially.
Senator Saxby Chambliss of Georgia called Hagel by his first name and exchanged jokes with him during his testimony. He served alongside Hagel in the Senate.
But Hagel years ago angered many Republicans by breaking with his party over the handling of the Iraq war.
It was one of several contentious chapters of modern U.S. history that surfaced during the session, from the Vietnam War, where Hagel served as an infantryman and was wounded, to former President Ronald Reagan's call for nuclear disarmament.
Hagel, who would be the first Vietnam veteran to serve as Pentagon chief, also was questioned on his view of the Pentagon budget. He is known as an advocate for tighter spending controls.
'WRONG' MAN FOR THE JOB
Even before Hagel started speaking, James Inhofe, the panel's senior Republican, called him "the wrong person to lead the Pentagon at this perilous and consequential time."
"Senator Hagel's record is deeply troubling and out of the mainstream. Too often it seems he is willing to subscribe to a worldwide view that is predicated on appeasing our adversaries while shunning our friends," said Inhofe of Oklahoma.
McCain's harsh attitude toward Hagel - whom he also singled out for opposing Obama's increase of forces in Afghanistan - was a far cry from their past, warm ties. McCain campaigned for Hagel in his Nebraska U.S. Senate race in 1996, and Hagel was national co-chairman of the Arizona Republican's unsuccessful 2000 presidential bid.
On Thursday, McCain said concerns about Hagel's qualifications ran deep.
"Our concerns pertain to the quality of your professional judgment and your world view on critical areas of national security, including security in the Middle East," he said.
In the entire Senate, which would vote on Hagel if he is cleared by the committee, only one of the 45 Republicans - Mississippi's Thad Cochran - has said he backs Hagel.
Senators Marco Rubio of Florida and Dan Coats of Indiana on Thursday joined the list of Republicans who said they would vote against Hagel.
(Additional reporting by David Alexander; Editing by Warren Strobel, Jackie Frank and Peter Cooney)