WASHINGTON — An investigation into whether retired Army Gen. David H. Petraeus illegally shared classified information will be conducted fairly, Attorney General Eric H. Holder said Sunday in the wake of reports that federal prosecutors have recommended that Petraeus be charged.

Holder, or his successor, would have to make the final decision about whether to file felony charges. Petraeus is suspected of sharing classified information with his mistress while serving as CIA director.

Holder said he would not comment on an ongoing investigation. But he said on ABC’s “This Week” that “any investigation that is ongoing will be done in a fair and an appropriate way.”

Petraeus led U.S. forces in Iraq during the surge that turned the tide of the war there and is credited with drafting the military’s counterinsurgency doctrine. He also commanded NATO troops in Afghanistan before taking over the CIA. He was popular politically until the affair with his biographer came to light and he resigned.

He has admitted showing poor judgment in having the affair but said he never gave the woman classified information. Law enforcement agents have reportedly found such material on her home computer in North Carolina.

Asked on CNN’s “State of the Union” about the reports, Democratic Sen. Dianne Feinstein of California defended Petraeus and argued against charges.

“This man has suffered enough, in my view,” she said. “… People aren’t perfect. He made a mistake. He lost his job as CIA director because of it. I mean, how much do you want to punish somebody?”

Petraeus’ attorney has not commented on the prosecutors’ recommendation to file charges.