* Hagel's trip will be closely scrutinised by Republicans
* First trip after bitter confirmation battle
* Will meet Karzai and talk to U.S. commanders and troops (Adds quotes, details)
By Phil Stewart
KABUL, March 8 (Reuters) - Chuck Hagel arrived in Afghanistan on Friday for his first trip abroad as U.S. defence secretary, seeking to make his own assessment of America's longest war as it enters its final stretch.
Hagel said he would meet U.S. commanders and troops, and hold talks with Afghan President Hamid Karzai, whose recent orders to curtail U.S. military activity underscore an often tense relationship with the 66,000 American forces there.
Hagel praised the sacrifices of American troops in Afghanistan.
"As I begin my time as secretary of defence, I look forward to hearing from you, seeing this war from your vantage point and working to make sure you get what you need to finish the fight and come home safe," he said.
Hagel said it was his first trip to Afghanistan since a mid-2008 visit with then-Senator Barack Obama during Obama's campaign for the presidency. Obama, a Democrat, forged a close bond with Hagel, a Republican, and remarked later that summer that the two agreed on almost "every item" of foreign policy.
That included the Iraq war. Hagel was an early Republican critic of the Iraq war, angering party allies in the Senate. They fiercely opposed his nomination to become Obama's defence chief but lacked the votes to stop it.
Hagel was confirmed on Feb. 26 and was sworn into office the next day.
Hagel's advice may help shape some of Obama's most lasting decisions in Afghanistan, notably how large a residual mission to keep there once NATO wraps up its combat mission at the end of next year and the vast majority of foreign forces go home.
"I need to better understand what's going on," Hagel told reporters as he flew to Kabul on the unannounced visit, adding his goal was to "make my own assessment and listen to our commanders".
On Tuesday, the outgoing head of the U.S. military's Central Command, General James Mattis, disclosed that he recommended keeping 13,600 American troops in Afghanistan - above the range of troop levels U.S. officials have said were being considered by the White House and discussed by NATO defence chiefs last month. [ID: nL1N0BXGWZ]
"I think it is important, General Mattis - all of our commanders - have an opportunity for their input. The president wants that, needs that, welcomes that," Hagel said, without disclosing his own thinking. He said Obama had not made a final decision.
Obama last month announced the withdrawal of 34,000 American troops - about half the total - by early next year. Officials also have outlined the expected pace of the withdrawal through next April.
Hagel, a decorated Vietnam veteran with shrapnel wounds in his chest, played down links between Vietnam and the grinding, counter-insurgency battle in Afghanistan. Despite 11 years of fighting and significant gains in Afghanistan, the Taliban remains resilient and enjoys safe havens across the border in Pakistan.
"As to the parallels to Vietnam, there are always parallels to any war," Hagel said.
Talking in broad terms about the end of the U.S. combat mission, Hagel remarked at one point to reporters: "It was never the intention of the United States to stay in Afghanistan indefinitely."
He added that did not mean the residual U.S. force after 2014, whatever size that would be, was not also significant - pointing to lasting U.S. military contingents in Europe, South Korea and Japan. But the role of the U.S. mission would change as Afghans take charge of their security.
"If you look at the role that we've had for the past 12 years as the lead combatant in Afghanistan, that's a totally different role than what we're transitioning into," Hagel said.
Asked about how the war would end, Hagel said: "I think we are transitioning in a way that gives the Afghan people a very hopeful future."
Hagel's visit to Kabul comes after Karzai has taken steps to limit U.S. military activities. On February 13, a NATO air strike requested by Afghan forces killed 10 people - including five children and four women - in the eastern province of Kunar, prompting Karzai to ban his troops from requesting foreign air strikes.
Two weeks later he halted all special forces operations in the central province of Wardak after a series of allegations involving U.S. special forces soldiers and Afghan men said to be working with them.
Asked whether limits on U.S. operations would be discussed with Karzai, Hagel said: "I look forward to talking with the president about many issues. And that, certainly, I'm sure will be one of them."
Hagel, in his message to troops, said he believed putting Afghans in full control of their country's security by the end of next year was a "clear and achievable" goal.
"We are still at war, and many of you will continue to experience the ugly reality of combat and the heat of battle." (Editing by Michael Georgy and Jon Hemming)