in Iraq, resigned last week to pre-empt revelations of an affair with biographer Paula Broadwell, a married army reservist.
Former CIA director David Petraeus and Paula Broadwell
The US commander in Afghanistan, General John Allen, is still under investigation over mails he sent a Florida socialite who blew open the affair when she complained to an FBI agent of threatening emails from Broadwell.
The scandal has rocked the Washington security establishment but, beyond any personal failings it may have revealed, Obama said he had seen no evidence it had harmed the security of the nation or its troops.
"I have no evidence at this point from what I have seen that classified information was disclosed that in any way would have a negative impact on our national security," he told his first news conference after his re-election.
"General Petraeus had an extraordinary career," he said. "But by his own assessment, he did not meet the standards that he felt were necessary as the director of the CIA with respect to this personal matter."
Petraeus is due to testify to Congress later this week on the September 11 assault in Benghazi, Libya, which killed four Americans including US ambassador Chris Stevens and two former Navy SEALs working for the CIA.
He took command of the CIA 14 months ago, retiring from the military after a storied career in which he commanded troops in Iraq and Afghanistan.
In probing Petraeus and Broadwell, the FBI happened upon a vast trove of messages Allen had sent Jill Kelley, a married 'social liaison' for US Central Command in Florida who hosted parties with Tampa-based officers.
It was Kelley's decision to inform an FBI friend she had received threatening emails -- that turned out to be from Broadwell -- that led to the investigation into Petraeus and his eventual resignation.
The White House has expressed confidence in Allen, after the four-star commander was placed under investigation by FBI agents.
The married general denies any sexual liaison with 37-year-old Kelley, but the volume of flirtatious correspondence could amount to "conduct unbecoming an officer," informed sources have said.
Allen had been due to face lawmakers this week for a hearing to confirm his promotion to the post of NATO's supreme commander in Europe, but Obama has put his career on hold until the Pentagon completes its investigation.
Lawmakers have accused the FBI of withholding information about the inquiry from congressional oversight committees, but Obama told reporters he could not interfere in the investigations under way, and would await their conclusions.
"I am withholding judgment with respect to how the entire process surrounding General Petraeus came up," he said.
"And we don't have all the information yet. But I want to say I have a lot of confidence generally in the FBI."
Petraeus resigned last week when it became clear his affair with Broadwell, who traveled to Afghanistan to write a fawning biography of him, would soon become public.
Broadwell has hired Washington power attorney Robert Muse to represent her. No criminal charges have been filed, but FBI agents searched her North Carolina home earlier this week and seized several boxes and pictures.
US media reports Wednesday suggested some classified material had been found, but nothing that would trigger a security alert.
The emails Broadwell sent to Kelley suggest the biographer was jealous of the socialite's rapport with generals, including Allen and Petraeus.
US media reported that Broadwell had criticized Kelley to senior generals under the online pseudonym KelleyPatrol, including one mail to Allen in which she called Kelley a 'seductress.'
Broadwell was photographed on Wednesday in Washington, staying at her brother's house, but has not addressed the media scrum camped outside.