* Petraeus to be solo witness before House, Senate panels
* Acting CIA director, others testified on Thursday
By Susan Cornwell
WASHINGTON, Nov 16 (Reuters) - Former CIA Director David Petraeus will testify Friday on Capitol Hill about the recent attack on the U.S. diplomatic mission in Benghazi, Libya, but is also expected to be asked about his resignation last week over an extramarital affair.
Petraeus has been invited to testify behind closed doors to the House of Representatives and Senate intelligence committees that are probing what happened in Benghazi on Sept. 11 when attacks by militants on the mission and nearby CIA annex killed the U.S. ambassador to Libya and three other Americans.
Lawmakers said on Thursday that the subject of Petraeus' affair and resignation is also likely to be raised, at least in so far as lawmakers want to know whether it had any impact on national security.
"I'm sure that issue will come up," said C.A. Dutch Ruppersberger, the top Democrat on the House Intelligence Committee.
Petraeus and his biographer, Paula Broadwell, have said that their affair did not put national security at risk - a central question hovering over the scandal that brought down one of the United States' most respected public figures last week.
FBI agents have found a substantial amount of classified information on Broadwell's personal computer since they searched her Charlotte, North Carolina, home with her consent on Monday.
Sources briefed on the investigation said the documents date from before August 2011, when Petraeus took up his post at the CIA and the two started their affair. None of the material comes from the CIA.
Petraeus has told the television network HLN that he resigned from the CIA because of the affair, not the attacks in Benghazi.
The assault on the U.S. mission in Benghazi has turned into a flash point between President Barack Obama and Republicans who accuse Obama's administration of misleading the public in the days following the attack.
Administration officials say their initial comments that it appeared the attack grew spontaneously out of protests over an anti-Muslim film rather than a premeditated strike were based on the best available information at that time.
Before his resignation, Petraeus had gone to Libya to interview people about what happened in Benghazi, Senate Intelligence Committee Chairwoman Dianne Feinstein said on Thursday. "So the opportunity to get his views, I think is very important."
"We'll get his (Petraeus') perspective on what information he knew and how his assessment of that intelligence changed over time," said Democratic Representative Adam Schiff, a member of the House intelligence committee.
Before his resignation, Petraeus had been scheduled to testify on Thursday at closed Senate and House intelligence committee hearings on the Benghazi attack.
Instead, acting CIA Director Mike Morell was a witness Thursday along with other U.S. officials from the FBI and intelligence community. Petraeus will be a solo witness before the same panels on Friday.
The CIA said on Thursday it had opened an "exploratory" investigation into Petraeus' conduct, building on what started as an FBI probe. Law enforcement officials have said they believe the FBI investigation is likely to end without criminal charges.