Washington - The CIA said Thursday that it had opened an "exploratory" investigation into the conduct of former Director David Petraeus, who resigned after admitting to adultery, and Defense Secretary Leon Panetta ordered the military services to consider how to strengthen ethics standards "that keep the military well led and well disciplined."

The CIA and Pentagon reviews stem from the resignation of Petraeus, a retired Army general, and revelations that Marine Corps Gen. John Allen exchanged possibly inappropriate emails with the woman who triggered the FBI investigation that exposed Petraeus' affair.

The military also has been rattled by a slew of lesser-known, more serious cases, including a general recalled from Afghanistan who is facing criminal charges of sexually assaulting or committing adultery with five women. The Pentagon, however, said the timing of Panetta's directive was "coincidental."

The FBI, meanwhile, was trying to determine if Paula Broadwell, the Army Reserve intelligence officer with whom Petraeus was romantically involved, had the security clearances needed to possess all of the classified materials found on her personal computer, according to a senior law enforcement official, who spoke on the condition of anonymity to discuss the sensitive subject.

"There are levels of clearance that she may not have had authorization for certain documents," the official said. "That's what they're really trying to sort out is classification levels, clearance levels."

The FBI investigation could take a while, the official said, because the bureau wants "to conduct a thorough investigation to see if there was any classified information that was either compromised or mishandled. That's something (the FBI takes) very seriously."

Security clearances for Broadwell, who allowed the FBI to search her home in Charlotte, N.C., Monday night and remove two computers, were withdrawn by the Army on Wednesday.

The preliminary investigation of Petraeus by the CIA inspector general's office was apparently aimed at assessing his general conduct during his 14-month stint as director.

"At the CIA we are constantly reviewing our performance. If there are lessons to be learned from this case we'll use them to improve," said a statement quoting an unnamed CIA spokesperson. "But we're not getting ahead of ourselves; an investigation is exploratory and doesn't presuppose any particular outcome."

The scope of the investigation wasn't disclosed.

Petraeus will testify today at closed-door hearings of the House and Senate intelligence committees on the circumstances surrounding the Sept. 11 attacks on the U.S. consulate and a nearby CIA annex in Benghazi, Libya. They resulted in the deaths of four Americans, U.S. Ambassador Christopher Stevens, a State Department staffer and two CIA contract security officers.

The attacks ignited a political firestorm, with critics questioning whether the Obama administration had provided adequate security, reacted properly and offered accurate accounts of what happened.

Panetta's order to Army Gen. Martin Dempsey, chairman of the Joint Chiefs of Staff, for the ethical standards review by the service chiefs was announced in Bangkok, Thailand, which the defense secretary was visiting.