- The White House has struggled to find a successor for Chuck Hagel as Defense Secretary
- An early top choice, Michele Fournoy, removed her name from consideration
- The new frontrunner is Ashton Carter, a former Pentagon official with years of DOD experience
- DHS Secretary Jeh Johnson is also a possible nominee
Washington (CNN) -- Ashton Carter, the former second-in-command at the Pentagon appears to be the top choice to replace outgoing Secretary Chuck Hagel, an administration official tells CNN.
While other candidates could emerge, a separate official acknowledged that Carter is very high on the list of possible candidates as the White House has made it clear an announcement is likely to come very soon.
The candidates for Secretary of Defense An administration official tells CNN that Homeland Security Secretary Jeh Johnson, a former General Counsel at the Pentagon, is also still on the list of possibilities. But the prospect of an additional confirmation hearing for Johnson's replacement if he were to move to the Pentagon as the Senate switches to Republican control could be too problematic for the White House.
Chuck Hagel out as defense secretary 
Pentagon: U.S. putting more boots in Iraq Related: Was Hagel doomed from the start?
Hagel announced his resignation last week, but has said he will stay on until his successor is confirmed by the Senate.
Carter, who served as Deputy Defense Secretary under both Leon Panetta and Hagel, would bring a wide range of experience to a department confronting multiple crises in the Middle East and preparing to enter a new phase in Afghanistan as the NATO combat mission ends.
Carter's ability to hit the ground running from his past experience at the Pentagon, in addition to the respect many senior military leaders have for him are seen as major benefits to winning confirmation should Obama nominate him.
"His career has sort of prepared him perfectly for this kind of a moment," says Michael O'Hanlon, a defense industry analyst at the Brookings Institution.
In addition to a broad understanding of the Pentagon bureaucracy, Carter is seen as a master of managing large budgets, a premium in the present era of continued belt tightening on Capitol Hill, as well as an expert on weapons acquisitions.
Related: White House struggles to find Hagel successor
He also has a firm grasp on understanding the trends and technology of warfare in the future.
"On paper and in terms of his resume and preparation you probably couldn't do much better," O'Hanlon said.
But Carter does lack certain experience shared by Hagel, Panetta had and many other secretaries - first--hand military experience. Carter has extensive experience at the Pentagon and in academia, but he was never actually in the military.
"You can always find things that you would have loved in a hundred year life span to have seen everyone do before they take this job, but realistically he has accomplished about as much as you could ask," O'Hanlon said.
Pentagon: Resignation not about Iraq 
Defense Secretary Hagel to step down Whoever is ultimately selected may not have much opportunity to make a mark at the Pentagon. They'll likely have less than two years likely on the job after confirmation. The next defense secretary will confront the specter of another possible round of automatic budget cuts known as sequestration to navigate with Congress, along with a White House known by some for micromanaging foreign and defense policy.
While Carter was always seen likely on Obama's short-list of candidates, his name gained prominence following the withdrawals from consideration by former Pentagon official Michele Flournoy and Sen. Jack Reed that they not be considered for the post.
Carter, who does not have a background as a political operative, is believed to be open to returning to the Pentagon, and would likely generate a smooth confirmation process officials tell CNN.
He was previously a professor at Harvard's Kennedy School, and was recently listed as a senior executive at the Markle Foundation.
CNN's Jim Acosta contributed reporting from the White House
A Palestinian man argues with Israeli police officers as he waits to get permission to enter the Temple Mount on Wednesday, November 5, in Jerusalem. Police clashed with Palestinians there on Wednesday, leaving more than 15 people injured in the latest round of unrest at the holy site. 
An Israeli soldier aims tear gas during clashes with Palestinian protesters following a rally Sunday, November 2, at a checkpoint between Jerusalem and the West Bank city of Ramallah. Tension in Jerusalem is perhaps at its greatest since the end of the second intifada, or Palestinian uprising, 10 years ago -- stoked by a rash of what some call hate crimes and others acts of terror. 
Right-wing Israelis are stopped by Israeli policemen as they try to access the al-Aqsa Mosque compound, part of the Temple Mount, on November 2. The Temple Mount is the holiest site in Judaism and the third-holiest site in Islam. 
Israeli border police block a road in Jerusalem as Muslims pray Friday, October 31. A day after taking the rare step of closing the Temple Mount, Israel partially reopened access for Muslim prayers Friday. But midday access was granted only to men over 50 and women. Israeli police said this was meant to prevent demonstrations by young Muslim men following the recent shootings of a controversial rabbi and a Palestinian suspect in the rabbi's shooting. 
Israelis walk at the Jewish quarter in the Old City overlooking the Temple Mount on October 31. 
Israeli police detain activist Noam Federman after he tried to enter the Temple Mount on Thursday, October 30. The closing of the holy site -- the first in more than a decade -- infuriated Palestinians, with a spokesman for Palestinian President Mahmoud Abbas calling it a "declaration of war." 
A van burns in Jerusalem during clashes between Palestinians and Israeli security forces on October 30. 
Israeli police scuffle with activists trying to enter the Temple Mount on October 30. 
Israeli police patrol Jerusalem during clashes on October 30. 
Palestinians throw stones in the streets of Jerusalem on October 30. 
Israeli police surround the Jerusalem home of Mu'taz Ihjazi on October 30. Police spokesman Mickey Rosenfeld said Ihjazi, a Palestinian suspect in the shooting of Rabbi Yehuda Glick, was shot and killed after he opened fire on police. Glick, an advocate of Jewish prayer rights on the Temple Mount, was shot after he gave a presentation in Jerusalem on Wednesday, October 29. 
Israeli demonstrators wave flags outside the Menachem Begin Heritage Center, where Glick was shot in Jerusalem on October 29. 
Israeli emergency personnel carry a body outside a synagogue on Tuesday, November 18, in the deadliest attack in Jerusalem in six years. Armed with knives and axes, two Palestinian men broke into the synagogue in the Har Nof area of western Jerusalem, killing four worshippers and wounding six others, Israeli police said. 
Emergency workers carry a body from the synagogue on November 18. Three of the men killed were dual Israeli-U.S. citizens, and the fourth was a dual British-Israeli citizen, an Israeli police spokesman said. 
A woman cries near the synagogue while looking on the scene of the attack November 18. Jerusalem has been on edge after a series of deadly stabbings and vehicle attacks. 
Response teams clean blood from the scene November 18. Police also shot and killed the attackers. 
An emergency responder wipes blood off the street outside the synagogue November 18. 
People appear dazed outside the synagogue after the attack November 18. 
People watch responders at the scene of the attack November 18. The FBI will investigate the synagogue attack because three victims were U.S. citizens, a U.S. law enforcement official said. 
A response worker navigates the scene of the attack. 
The body of a Palestinian attacker lies covered on the rails at a Jerusalem light train station on Wednesday, November 5. A police spokeswoman said the man was shot and killed after he deliberately rammed his vehicle into a crowd of pedestrians, then got out of the vehicle and attacked people with a metal bar. One pedestrian, an Israeli border police officer, was killed and 14 other people were injured. 
Police and investigators inspect the van used in the hit and run. Police said the suspect ran over three border police officers waiting to cross the road, then drove into pedestrians standing at the train station. 
Police officers patrol the scene of the attack. A police spokesman called the incident a terrorist attack. 
Israeli firefighters inspect the scene of the attack. Police identified the driver as a member of the militant Islamic group Hamas. 
Onlookers gather at the crime scene. A police spokeswoman said the attacker was 38 years old and had been released from prison recently. 
Rescue workers and paramedics carry an injured man to an ambulance. 
Investigators inspect the scene. 
Investigators look over the vehicle used in the attack. A witness said he heard police fire about 20 shots at the suspect.