WASHINGTON -- As US Defense Secretary Chuck Hagel is stepping down, President Barack Obama is likely to choose a new defense chief who can play ball with the rest of the team, experts said.

Hagel has butted heads with the White House over a number of issues, including how to deal with the onslaught of the Islamic State, a terror group also known as ISIS that has overrun vast swaths of Syria and northern Iraq in a bid to establish its own nation based on a twisted version of Islam.

While initially Hagel's focus was on making military cuts, that changed abruptly when the Islamic State began grabbing global news headlines and the administration shifted its focus toward combating the extremists. As time went on, Hagel was seen to be more on board with US generals than with the White House, and the administration resented his independence, some experts said.

Obama may have a hard time finding a replacement who is not only right for the job but who will also be a team player.

"The next defense secretary will be someone who basically is going to do what the administration wants. It seems that they butted heads over ISIS and the state of the global landscape," Republican strategist Ford O'Connell told Xinhua, speaking about the relationship between Hagel and the White House.

"They want someone who is willing to tow the administration line, and Hagel was not that person," he said. "When things got crazy with ISIS and Russia, he was saying very different things than the administration."

Darrell West, a senior fellow at the Brookings Institution, told Xinhua that Hagel's departure signals the need for a different kind of defense secretary.

"Hagel was brought into the cabinet to help Obama wind down the Iraq and Afghanistan wars," he said. "But circumstances have changed now with the emergence of ISIS in the Middle East and the Taliban in Afghanistan. Obama feels he needs someone who is tougher on foreign policy in order to execute the new strategy. The main challenge for the new appointment will be devising a strategy to confront ISIS and deal with new threats that are emerging around the world."

The rapid advancement of ISIS has alarmed the United States, as Washington's worst nightmare is another attack on the homeland like the Sept. 11, 2001 strikes on New York City and Washington, D. C.

The ISIS has threatened to "fly the flag of Allah in the White House," and the United States has in recent months launched an air- bombardment campaign against the militants, although some have blasted it as weak.

Obama announced earlier this month that he will deploy an additional 1,500 US troops to Iraq as advisers, around three years after the president pulled out the last US troops from the war-torn country, but experts question whether the move will have any impact at all.

Hagel's departure means Obama will find his fourth secretary of defense, and it is rare in US history for one president to go through so many defense secretaries.

Two possible replacements are former Deputy Defense Secretary Ashton Carter and former Undersecretary of Defense Michele Flournoy, who are both viewed as capable.

Flournoy confirmed to the Politico newspaper that she has taken herself out of the running to succeed Hagel.