In testimony during a City Council oversight hearing yesterday, the chairman of a mayoral agency designed to serve as an independent monitor of possible corruption within the New York Police Department said his office has had “significant difficulty” fulfilling its mission because of “lack of cooperation” by police officials in disclosing information.

The chairman, a former federal prosecutor, Mark Pomerantz, testified that the Commission to Combat Police Corruption has been unable to investigate areas of potential corruption within the department because requests to furnish his office with necessary documents and internal records were routinely denied.

As a result, reports on potential abuses in overtime pay and on alleged sexual and domestic misconduct among off-duty officers have been sidelined indefinitely.

“We write letters, we have meetings, and nothing happens,” Mr. Pomerantz said.

He added that without the prosecutorial authority to compel agencies such as the Police Department to provide internal information in a timely fashion, his $500,000-a-year agency has become ineffective.

Officials within the department have been helpful and amiable, Mr. Pomerantz said. The lack of cooperation is due to “disputes over jurisdiction,” he said – areas of concern where police officials felt the commission lacked authority to investigate.

One of those areas is abuse in overtime pay, Mr. Pomerantz said. While much of the already-shrinking police force is strained as counterterrorism measures force officers to work longer details, overtime abuse among officers has been a concern. But when the commission requested overtime records to analyze information and compile a report, Mr. Pomerantz said, department officials rebuffed the request, saying overtime abuse was an internal management issue, not a corruption issue.

Asked by the chairman of the council’s public safety committee, Peter Vallone Jr., a Democrat of Queens, how long the battles of jurisdiction had crippled the effectiveness of his office, Mr. Pomerantz replied, “I think it would define the entirety of my 18 months [as chairman].”

A police spokesman, Paul Browne, disputed the commission’s claim that information was not being provided. “In each and every case where misconduct rose to a level meriting a corruption investigation, the commission was given full access to case files and other information pertaining to the quality of the department’s corruption-fighting efforts,” Mr. Browne said in a statement. “That has been true for domestic incidents, sexual misconduct, and overtime fraud. It would also be true for any instance in which misconduct involving the recording of crime statistics rose to the level of serious corruption.”

Earlier in the hearing, too, police officials disputed the accuracy of the commission’s reports.

In February, the commission released a report critical of the department’s screening process for applicants and found that in some cases, thorough background checks weren’t completed. The chief of the department’s Personnel Bureau, Rafael Pineiro, testified that a review of the report found the commission’s charges without merit.

Mr. Pomerantz testified, however, that six weeks before his report on background checks was released, the commission sent an advance copy of the report to the department for fact-checking.

There was no response from the police department, Mr. Pomerantz said, until the day after the report was released.

“That’s outrageous,” Mr. Vallone said, adding that the commission’s inability to obtain information reinforced the argument that the police should not have the responsibility of policing themselves. He echoed a concern raised by Council Member Oliver Koppell, Democrat of the Bronx, who introduced legislation in the City Council last year to establish an independent monitor with prosecutorial powers.

Under current laws, the mayor is the only city official with the power to create such an agency – and one that could become a political risk.

“No mayor would want to have an independent agency that would take away the power to control his police force,” Mr. Koppell said. A spokesman for Mayor Bloomberg did not return calls. According to police officials, there is little need to form an independent agency, especially considering that the number of corruption cases has decreased dramatically in the past few decades and the nature of corruption has changed from “systematic” to “opportunistic.”

“Corruption mutates,” the chief of the department’s Internal Affairs Bureau, Charles Campisi, testified yesterday.

In 2004, less than one-quarter of 1% of police officers were arrested on criminal charges, 89 among a force of 37,000 officers, Mr. Campisi said.

Mr. Campisi said the more than 500 officers in his command were best suited to ferret out cases of corruption because police officers are most familiar with police culture.

“I wouldn’t say it’s a situation where the fox is guarding the henhouse,” Mr. Campisi said. “It’s more like the rooster.”