The last time Michael Armstrong was involved in keeping an eye on the police department, he was 38 years old and the chief counsel for a group of attorneys and investigators appointed by Mayor John Lindsay to confront pervasive corruption in New York’s police department in the wake of the Frank Serpico disclosures.

Now, 34 years and 10 police commissioners later, Michael Armstrong, 72, is again at the helm of a group of attorneys charged with monitoring corruption in the police department, the city’s Commission to Combat Police Corruption.

This time, however, the problem is not the diffuse, low-level bribe-taking cops of the era before the Knapp Commission or the drug-dealing officers operating before the Mollen Commission, he said. The question he is dealing with is: How does his commission “combat” police corruption when there doesn’t appear to be any of the systemic permissiveness and opacity of previous administrations?

“It’s an inherent problem when you have an auditing group that is supposed to audit an organization that seems to be operating very well,” Mr. Armstrong said. “The best formula for a corruption-free department is to have a tough, knowledgeable, hands-on police commissioner, and we have one. That doesn’t mean there aren’t problems.”

Mr. Armstrong’s predecessor, Mark Pomerantz, quit his position last summer after charging that the police department refused to give him access to documents and personnel.

“We write letters, we have meetings, and nothing happens,” Mr. Pomerantz testified at a City Council oversight hearing in April 2005, according to news reports. The problem, he said, was a dispute over jurisdiction on issues like abuse of overtime pay and alleged sexual and domestic misconduct by off-duty officers — issues that the police said were administrative business and not subject to the commission’s corruption investigations.

Ever since Mr. Pomerantz’s departure, Mr. Armstrong and the staff of the commission have pushed aside their investigative work to fine tune the boundaries between the commission and the police department’s own Internal Affairs Bureau. The goal is not only to clarify the roles of the two auditing bodies, but also to preserve the commission’s authority in the future, he said.

The commission does not have subpoena power except for in extreme circumstances through the Department of Investigation. Consequently they rely mostly on the police commissioner’s cooperation in getting access to the department.

“However good Kelly may be, if his predecessor was involved with the kind of problems that [Bernard] Kerik was involved in, it certainly illustrates the fact that good commissioners come and go,” Mr. Armstrong said. “One of the things I learned in the Knapp Commission is that you can have a cesspool where everyone looking at it thinks it is just a smooth lake.”

Commissioner Kelly said in an interview that he wants Mr. Armstrong’s commission to be more involved in the department’s day-today investigations as well as attend steering committee meetings.

“When we talk about corruption, we’re talking about crime,” he said. The internal affairs bureau, headed by Chief Charles Campisi, reports directly to the police commissioner and regularly conducts integrity and police impersonation investigations, he said.

The struggle to define the role of the commission is only the latest chapter in the city’s history of trying to set up the right apparatus to monitor the largest police department in the world. Before the Knapp Commission, the police department was monitored solely by its Internal Affairs Bureau. But in the aftermath of the widely televised hearings, the Mayor and governor set up a special prosecutor with the power to subpoena documents and conduct what Mr. Armstrong called “front-line investigations.”

Eventually Governor Cuomo dissolved that position, and the police department again went unmonitored by an outside agency. But after the Mollen Commission in the early 1990s the Commission to Combat Police Corruption was created to monitor the effectiveness of the department’s internal investigations. The Civilian Complaint Review Board, which has been in place in its current form since 1993, investigates reports of excessive or unnecessary force, abuse of authority, discourtesy, or the use of offensive language by police officers. It is not involved in corruption investigations.

For now, Mr. Armstrong said he is confident the department is worlds away from the Knapp Commission days. It’s the years to come that worry him: Without a strong commissioner, the corrupt minority of the department could recede into their old ways. And without a strong commission, those problems could go unhindered for years, he said.

Frank Serpico, 70, who runs his own Web site, frankserpico.com, said police corruption hasn’t gone away — it’s just hidden better. “I could tell you chapter and verse about e-mails I’m getting from cops all over the country who are trying to do the right thing and getting drummed out of the department,” he said. “Unless you have an agency that is going to support the honest guy and encourage them to do the right thing, nothing will change.”