Officials in the nation's largest police department said Friday they uncovered dozens of instances of crimes misreported and wrongly downgraded by officers at a precinct after an anonymous tip to internal affairs and now 19 officers face departmental charges.

The 19 New York Police Department employees — one lieutenant, eight sergeants, nine officers and one detective — worked at the 40th Precinct in the Bronx and face charges of misreporting during a four-month period last year. They face a loss of vacation days or possible dismissal from the department if they are found guilty.

Commissioner William Bratton, who took over the 35,000-officer department last year, has made it a priority to ensure crime complaints are accurately reported.

"The purposeful misrepresentation of crime data is rare but nevertheless unacceptable, and it will be dealt with accordingly," he said.

The department's Quality Assurance Division, under a risk management bureau tasked with weeding out problem officers, uncovered 55 instances in 1,558 complaints of crimes downgraded or misreported within the precinct. The officers were accused of downgrading or misreporting low-level crimes such as petit larceny, not killings, rapes or shootings.

The NYPD's deputy commissioner for legal matters, Lawrence Byrne, said accurate crime numbers are critical.

"We need the public to trust those numbers, and we make resource assignments of officers, how they spend that time, in large part based on those numbers," he said.

As a result, overall crime statistics for the precinct for last year have been recalculated from a previously reported crime decrease of 14 percent to a decrease of 11.4 percent.

The previous administration was plagued by allegations crime rates were low partly because officers were labeling higher-level crimes including rape as lower-level assaults to make precincts seem safer, but there was never any widespread proof.

The Quality Assurance Division conducts audits of crime reporting for all precincts, transit districts and housing patrol service areas. Enhanced audits are performed where anomalies are detected or suspected.

Byrne said he doesn't think the pattern is widespread. But the commanding officer of the 40th Precinct was reassigned, and police officials are auditing his previous command. The supervisor is not charged; police said he did not appear to know about the misconduct.

The head of the largest police officers' union, Patrick Lynch, said it's been a problem for a decade but officers are forced to do the bidding of their superiors.

"We agree that crime stats have to be accurate in order to know where and when to assign police resources," he said. "However, because of the serious shortage of police officers over the last decade and a half, management has consistently hammered police officers to reduce felonies to misdemeanors."

The president of the Lieutenants' Benevolent Association, Lou Turco, said the accused lieutenant would be exonerated.

"The department has tried and convicted these officers before they have had a chance to defend themselves," he said.