The probe is still in the planning stages, but would be a broad examination beyond the particulars of Army psychiatrist Nidal Malik Hasan, officials said. Defense Secretary Robert Gates wants a unified probe that hits all corners of the Pentagon, Pentagon Press Secretary Geoff Morrell said.
"This is shaping up to be a DoD effort," Morrell said, using shorthand for the Department of Defense.
"This is larger than the Army. There are issues that need to be looked at department-wide, and the focus at this point is trying to figure out some of those questions," he added.
The investigation would consider some questions Morrell described as immediate, although he would not be specific, and some he said will take longer to frame and sort through.
Another official said there will be a fast look at whether the military has missed red flags that might signal there are other potentially dangerous service members out there. That official spoke on condition of anonymity because the investigation is still being organized.
The Army has also been preparing to launch its own internal probe. The Pentagon review could supersede that, although it is not clear whether the Army will still go ahead separately.
Though it's still undecided who would do such a review and exactly what it would include, officials are working to make an announcement on it soon, a senior defense official said Tuesday on condition of anonymity because plans are still fluid.
Morrell said there has ben no decision on the structure, time line or staffing for a review.
"He's trying to come to a resolution of this as quickly as possible, but this has not been nailed down quite yet," Morrell said of Gates.
Hasan, an Army major, is accused of killing 13 people in the Nov. 5 shooting rampage at the Texas base.
Army Chief of Staff Gen. George Casey had said earlier that the service would take a hard look at itself following the Nov. 5 shooting.
Any new review would be have to be careful not to interfere with the ongoing criminal investigation, defense officials said. And so it could look at things outside that realm such as personnel policy and practices and whether there are adequate health services for troubled troops, one official said.
A top priority, this official said, likely would be to look at red flags missed in Hasan's case, with an eye toward ensuring there are not other similar missed cases out there waiting to happen.
"A tragedy like this certainly gives this institution an opportunity to reflect on whether we are doing everything that we can and should to prevent something like this from happening," said Defense Department spokesman Bryan Whitman. He said Gates has not made any decision on a defense-wide review.
Two military officials said Tuesday that Casey is looking at forming an investigative panel. It would look at Hasan as a whole, his career development and at what point someone should have or might have raised an alarm, one of the officials said. The other said the terms of what the panel would do have not been defined.
The proposed Army probe would focus on Hasan's six years at Washington's Walter Reed Medical Center, where he worked as a psychiatrist before he was transferred to Fort Hood in July, one said.
The doctors who oversaw Hasan's medical training had discussed at a meeting concerns about Hasan's overly zealous religious views and strange behavior months before the attack, a military official told The Associated Press last week. Hasan also was characterized as a mediocre student and lazy worker, but the doctors saw no evidence that he was violent or a threat. The military official spoke on condition of anonymity because the official was not authorized to speak publicly about the meeting.
The FBI learned late last year of Hasan's repeated contact with a radical Muslim cleric in Yemen who encouraged Muslims to kill U.S. troops in Iraq. President Barack Obama already has ordered a review of all intelligence related to Hasan and whether the information was properly shared and acted upon within government agencies.
The Senate Homeland Security and Governmental Affairs Committee on Thursday will hold its first public hearing about the incident. Obama on Saturday urged Congress to hold off on any investigation, pleading for lawmakers to "resist the temptation to turn this tragic event into the political theater."