Mayor Bill de Blasio's former campaign treasurer and nominee to lead the Department of Investigation Thursday faced relentless questioning by City Council members on whether his friendship with the mayor compromises his objectivity.

Mark Peters was grilled even by Speaker Melissa Mark-Viverito, herself criticized for being too close to de Blasio after the mayor lobbied council members on her behalf in the speaker's race.

"How do you feel that you can dutifully exercise -- fully -- independence and fulfill the responsibilities that this position calls for?" she asked.

Peters said his long career in "good government" was rooted in impartiality. He recalled fining former Gov. David A. Paterson $62,125 for improperly accepting World Series tickets when Peters was a member of the state Public Integrity Commission -- despite working for a past Paterson State Senate campaign and despite their two-decade friendship.

Peters testified before the rules committee for about 2 1/2 hours at City Hall. The council is scheduled to vote Tuesday on his confirmation.

"If you can't separate out your personal feelings from where the facts are taking you, you're not cut out for law enforcement," Peters said, adding, "I would investigate the mayor's office under the same circumstances that I would investigate any other agency."

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Peters, 48, an attorney at a private law firm, is a close friend of de Blasio and served with him on a Brooklyn school board.

As investigations commissioner, he would be charged with investigating corruption, fraud and waste and have the high-profile task of appointing an NYPD inspector general.

He said he would present a candidate for IG in the next 60 days and prefers someone with a background in New York law enforcement. The inspector general should have a staff and office separate from the Department of Investigation and NYPD, he said.

Peters said de Blasio would have "significant input" in the selection, a phrase that troubled Council Member Jumaane Williams (D-Brooklyn).

Williams said he is "grappling" with whether Peters would have the appearance of impartiality.

Asked about the council's concerns, mayoral spokeswoman Marti Adams referred to de Blasio's Jan. 18 statement nominating Peters and touting his "immense personal integrity."

Peters said that while he does not plan to update de Blasio every day on the investigations he conducts, but does need to be in regular communication with the mayor.

Dick Dadey, executive director of the watchdog group Citizens Union, testified Thursday that Peters is qualified and can maintain objectivity.