WASHINGTON » Top national security officials trudged to Capitol Hill today to grapple with fallout from the David Petraeus sex scandal as Defense Secretary Leon Panetta asked service chiefs to review ethics training for military officers. He said he was unaware of any other top brass who could turn out to be ensnared in the debacle.

One person missing from the tableau: Afghan war chief Gen. John Allen, whose nomination to take over in Europe is on hold because of suggestive emails turned up in the investigation.

Legislators went forward with a hearing on the nomination of Gen. Joseph Dunford to replace Allen in Afghanistan. But with Allen’s own future uncertain, they put off consideration of his promotion to U.S. European Command chief and NATO supreme allied commander. Allen had initially been scheduled to testify.

Panetta, speaking at a news conference in Bangkok, gave new words of support to Allen, voicing "tremendous confidence" in the general.

Citing a string of ethical lapses by senior military officers, however, Panetta asked the Joint Chiefs of Staff to review ethics training and look for ways to help officers stay out of trouble.

Sen. John McCain, R-Ariz., opened Dunford’s hearing with kind words for Allen, saying, "I continue to believe that General Allen is one of our best military leaders. And I continue to have confidence in his ability to lead the war in Afghanistan."

Leading administration officials, meanwhile, met privately with lawmakers for a third straight day to explain how the Petraeus investigation was handled and explore its national security implications. Among those appearing before the House Intelligence Committee: Director of National Intelligence James Clapper and Acting CIA Director Michael Morell.

Maryland Rep. Dutch Ruppersberger, the committee’s top Democrat, said after the hearing he was satisfied that the FBI had behaved properly in not notifying the White House or lawmakers about the inquiry sooner, in keeping with post-Watergate rules set up to prevent interference in criminal investigations.

But committee member Adam Schiff, D-Calif., said lawmakers would continue to ask questions because "there’s a lot of information we need … with respect to the facts about the allegations against General Petraeus."

Petraeus, the much-honored retired general, resigned his CIA post Friday after acknowledging an extramarital affair with his biographer, Paula Broadwell. The FBI began investigating the matter last summer but didn’t notify the White House of Congress until after the election.

The CIA today opened an "exploratory" investigation into Petraeus’ conduct. The inquiry "doesn’t presuppose any particular outcome," said CIA spokesman Preston Golson. At the same time, Army officials say that, at this point, there is no appetite for recalling Petraeus to active duty to pursue any adultery charges against him.

In the course of investigating the Petraeus situation, the FBI uncovered suggestive emails between Allen and Florida socialite Jill Kelley, both of them married. President Barack Obama then put Allen’s promotion nomination on hold.

Gen. Martin Dempsey, chairman of the Joint Chiefs of Staff, said he expects Allen to eventually take over the European Command, but he acknowledged, "I see this investigation and how long it could take affecting that."

Dempsey said he "absolutely" had confidence in Allen’s ability to continue in command in Afghanistan despite the distraction of the scandal. He spoke in an interview with American Forces Press Service.

While Allen’s nomination has been put on hold, the fact that it wasn’t immediately withdrawn suggests there is at least some feeling that he could survive the investigation.

The initial expectation is that the Defense Department inspector general’s probe into the emails will be done within weeks rather than months. The final decision would likely be made by Panetta and the White House after discussions with Capitol Hill leaders.

Even if Allen’s move to NATO is shelved, Dunford’s nomination to take Allen’s place as the top U.S. commander in Afghanistan will move forward.

Panetta this week sent Dempsey a memo asking the Joint Chiefs to brainstorm "how to better foster a culture of value-based decision-making and stewardship" among senior officers and their staff. In other words: come up with a game plan for ending bad behavior.

"As has happened recently, when lapses occur, they have the potential to erode public confidence in our leadership and in our system for the enforcement of high ethical standards," Panetta wrote. "Worse, they can be detrimental to the execution of our mission to defend the American people."

Panetta didn’t mention Petraeus in the memo, and the defense chief’s spokesman said the request for an ethics review was in the works before the Petraeus matter came to light.

Petraeus, in his first media interview since he resigned, told CNN that he had never given classified information to Broadwell. He also said his resignation had nothing to do with his upcoming testimony to Congress about the attack on the U.S. Consulate and CIA base in Benghazi, Libya, that caused the death of four Americans.

He told the network he wanted to testify about the Libya matter. And he’ll have that opportunity on Friday, when he appears before the House Intelligence Committee. Committee officials planned to limit the subject of that hearing to Libya, ruling out questioning about the affair with Broadwell and any potential national security implications.

Both Petraeus and Broadwell have said she didn’t get any classified documents from him. But the FBI has found a substantial number of classified documents on her computer and in her home, according to a law enforcement official. That official spoke only on condition of anonymity because the official was not authorized to speak publicly about the case.

Broadwell, a former Army intelligence officer, has told agents that she took classified documents out of secure government buildings. The Army has now suspended her security clearance.

Asked why the Justice Department did not inform the president and Congress regarding the investigation involving Petraeus, Attorney General Eric Holder said today, As we went through the investigation and looked at the facts and tried to examine them as they developed, we felt very secure in the knowledge that a national security threat did not exist."

Had there been a security threat, "we would of course have made that known to the president and also to the appropriate members on the Hill," the attorney general said at a New Orleans news conference on another topic.

In the absence of such a threat, "we do not share outside the Justice Department, outside the FBI the facts of ongoing investigations," he added. He said the department does not share information from criminal investigations so that such probes "can be seen as being done in an impartial way."

Burns reported from Bangkok. Associated Press writers Kimberly Dozier, Adam Goldman, Lolita C. Baldor, Pete Yost and Donna Cassata contributed to this report.