U.S. Attorney General Eric Holder speaks at a news conference in New Orleans November 15, 2012. (Jonathan Bachman/Reuters)

Attorney General Eric H. Holder Jr. on Thursday defended the Justice Department’s handling of the investigation that ledDavid H. Petraeus to resign as CIA director, saying that the department was right to keep the inquiry secret from the White House until after last week’s presidential election.

Holder’s first public comments on the controversy came as the CIA opened an internal inquiry of Petraeus’s conduct during his 14-month tenure as director. The move means that there are three active investigations related to a scandal that has scrambled President Obama’s national security team.

“What we did was conduct the investigation in the way we normally conduct a criminal investigation,” Holder said in a news conference in New Orleans.

He said the inquiry was handled “in an impartial way. We follow the facts. We do not share outside the Justice Department, outside the FBI, the facts of ongoing investigations.”

Holder’s remarks were aimed at quieting criticism that has grown sharper in recent days as the initial shock waves from Petraeus’s resignation have given way to questions about Justice Department decisions during its probe.

Some of those questions have focused on Fred Humphries, an FBI agent in Tampa whose concerns that the investigation had uncovered possible national security risks led to a chain of events that resulted in a House Republican leader raising the issue with the office of FBI Director Robert S. Mueller III. A person close to Humphries said he had no intention of being a whistle-blower, but the agent’s informal comments may have triggered the disclosure of Petraeus’s affair.

Republicans have accused Holder of withholding the results of the investigation until after the election for political motives. At the same time, some Democrats have begun to draw comparisons between the exposure of an adulterous affair by Petraeus and the bureau’s history of digging up dirt on Washington officials during the tenure of founding FBI Director J. Edgar Hoover.

“We don’t want to return to those days,” said Rep. Adam B. Schiff (D-Calif.), a member of the House intelligence committee and a former federal prosecutor. “The FBI was trying to find the right line here,” he said, even as it unearthed “what may have been an affair that had nothing to do with national security.”

Lawmakers from both parties have faulted the FBI for not notifying Congress that a criminal probe had turned up compromising material on the CIA director as well as potentially inappropriate communications between a Tampa socialite at the center of the case and Gen. John R. Allen, the U.S. military commander in Afghanistan.

Holder fired back Thursday, saying the Justice Department “made the determination as we were going through that there was not a threat to national security.” Because of that conclusion, he said, there was no reason to advise officials outside the department before the investigation was complete.

The FBI notified the executive branch with a call to Director of National Intelligence James R. Clapper Jr. on the evening of Election Day, Nov. 6. Holder said the call was made then because the bureau had “conducted a critical interview the Friday before. When we got to that point, we thought it appropriate to notify the president.”

Law enforcement officials said the “critical interview” was a Nov. 2 meeting with Paula Broadwell, the Petraeus biographer whose affair with the CIA director was exposed by the FBI investigation. The officials spoke on the condition of anonymity because they were not authorized to talk publicly.

Broadwell and Petraeus are both married. The case was triggered by harassing e-mails Broadwell sent to the Tampa woman, Jill Kelley, who was close to Petraeus and Allen, the commander of allied forces in Afghanistan.

It is unclear what FBI agents covered in that final interview with Broadwell, but the investigation has focused on her possession of classified material. She and Petraeus have denied that he was the source of any classified files.

The same question may now be at the heart of an internal CIA investigation of Petraeus’s conduct launched by the agency’s inspector general. Officials described the probe as “exploratory,” suggesting a broad inquiry into whether Petraeus’s personal transgressions crossed over into professional misconduct or created a security risk.

As CIA chief, Petraeus was charged with safeguarding some of the nation’s most precious secrets. He traveled extensively and has said through associates that his affair with Broadwell began shortly after he was sworn in.

“If there are lessons to be learned from this case, we’ll use them to improve,” CIA spokesman Preston Golson said. “But we’re not getting ahead of ourselves; an investigation is exploratory and doesn’t presuppose any particular outcome.”

Petraeus denied mishandling classified information in communications with a CNN reporter, according to a report by the cable news channel on Thursday. The reporter, Kyra Phillips, said that the retired general told her that he “had engaged in something dishonorable,” that he has not been in communication with Broadwell since their affair was exposed and that “he insisted to me that he has never passed classified information to Paula Broadwell.”

The former CIA boss is scheduled to testify in closed-door sessions Friday morning with the House and Senate intelligence committees. But Petraeus has said that he will discuss only the Sept. 11 attack on a U.S. diplomatic outpost in Benghazi, Libya, in which four Americans were killed.

The inspector general at the Defense Department has initiated an investigation of hundreds of e-mails exchanged between Kelley and Allen.

New information about the investigation indicates that Allen may have received the first harassing e-mail from Broadwell in mid-May through one of several alias accounts she set up.

Law enforcement officials have said Broadwell’s e-mails were aimed at souring Kelley’s relationships with Allen and Petraeus. Both men have denied having a physical relationship with Kelley, who was a volunteer at MacDill Air Force Base in Tampa, where both generals were based before their separate tours in Afghanistan.

Allen’s associates have said he did nothing wrong, but U.S. officials have said the e-mails he exchanged with Kelley were sexually explicit and inappropriate.

Allen forwarded Broadwell’s warning to Kelley, officials said. In the following weeks, Kelley and her husband, Scott, began receiving harassing messages on their joint e-mail account, prompting Kelley to consult Humphries, the FBI agent whom she had known for some time.

Humphries turned over copies of the e-mails to the bureau. Concerned that the sender had intimate knowledge of Petraeus and Allen’s schedules, the FBI began an inquiry that over months would accumulate thousands of pages worth of documents, including details of the personal lives of two top national security officers.

In August, Kelley was told that Broadwell had sent the e-mails. At some point, Petraeus learned of the messages and urged Broadwell to stop sending them, officials said. Senior Justice Department officials were not informed of the probe until late summer.

Holder’s explanation of the timing of the FBI’s disclosure to the administration runs counter to speculation that the bureau revealed the investigation’s existence because Humphries’s concerns had made their way to House Majority Leader Eric Cantor (R-Va.) on Oct. 27. Four days later, Cantor’s office contacted Mueller’s staff to express concern about a possible breach of national security involving Petraeus.

“We felt very secure that a national security threat did not occur that warranted sharing,” Holder said at a news conference called to announce a $4 billion settlement with BP over the 2010 Gulf of Mexico oil spill.

Aspects of the investigation remain open. FBI agents searched Broadwell’s home in Charlotte on Monday night for evidence that she had classified files.