SAN JOSE — Even as community complaints against San Jose police officers rise, cops have almost entirely stopped the practice of tipping off their superiors to misbehaving colleagues — resulting in far fewer officers being punished.

New figures from Chief Larry Esquivel show that compared to a few years ago, the department last year launched 83 percent fewer investigations into police department employees based on evidence submitted by fellow officers. Those complaints are key in helping San Jose determine whether an officer needs to be disciplined or trained, yet last year only 1 percent of the police force was investigated based on allegations from their colleagues.

“It’s very troubling, and I hope that the chief would have an explanation for this at next week’s meeting” when the City Council discusses the new figures, Vice Mayor Madison Nguyen said.

Police say it’s possible the number of complaints is down because cops are simply behaving better. They point to new training programs that may have helped officers’ conduct. Yet in allegations ranging from improper force to rude language, residents filed more misconduct complaints against the police force last year than at any point in the past four years.

The internal affairs unit, under the direction of the chief, emphasized it looks into all complaints cops submit about their fellow officers.

“From an IA point of view, we’re not sure what’s causing the decreases,” said Lt. Loyd Kinsworthy, the IA commander.

A South Bay civil rights group, however, expressed concern that cops may be ignoring behavior they once reported.

“The last thing you want, particularly for a police department, is officers protecting bad behavior and bad actors,” said Raj Jayadev, coordinator for the Silicon Valley De-Bug community group, which has criticized the Police Department. “That’s the point where really it becomes a danger to the community.”

Some in the department, speaking on background, said the police force is now so short-staffed that supervisors — long the main source for evidence on misbehaving officers — no longer have time for such responsibilities as they focus on more pressing day-to-day issues.

The statistics mirror an overall trend of declining investigations at the department, which has seen the number of arrests and the percentage of crimes that are investigated drop in half in the past half-decade, even as crime has increased. At the same time, the number of officers has dipped from about 1,400 to 1,000 in the past decade as the city struggles to afford its cops, and officers leave for better-paying cities after pension cuts voters approved in 2012.

The internal affairs team must investigate all complaints about officers, dispatchers and other police employees. But the allegations that originate from officers are especially key because about three-quarters of those complaints are ultimately confirmed and lead to punishment or counseling.

In 2010, following similar numbers from 2009, internal affairs acted on tips from its own department to initiate 84 administrative investigations, covering 118 allegations of misconduct from police employees, mainly officers. After steady decreases in 2011 and 2012, last year the department initiated just 13 investigations covering 16 allegations of misconduct.

As a result, the department went from launching nearly seven officer-initiated investigations per month to about one per month.

Most of the officers who violated department policy for a range of administrative infractions typically received training or counseling, or a short suspension. Most offenses fell into two categories — conduct unbecoming of an officer and violating police procedure — but Esquivel’s report does not spell out specific acts of misconduct.

Some complaints are more serious, however. From 2009 to 2012, four to six police employees per year were fired after officer-initiated investigations. But no one was terminated last year.

In all, the number of officers punished from investigations stemming from officer tips plummeted 61 percent last year compared to 2009 and 2010. The reporting of the figures didn’t begin until summer 2008.

Police union head Sgt. Jim Unland said he views the plummeting investigation numbers as a positive development. “It is a testament to the dedication and professionalism of our remaining officers that the number of department initiated complaints has declined so dramatically,” Unland said in a statement.

But retired Judge LaDoris Cordell, the city’s independent police auditor, said she expects the council to grill the police brass at the April 29 meeting over why the officer-initiated IA investigations have plummeted — though she, too, did not have an explanation.

“Why is there this dramatic drop?” she asked.

Contact Mike Rosenberg at 408-920-5705. Follow him at Twitter.com/RosenbergMerc.