An unexpected exodus of Baltimore police officers in the days and weeks before cuts to their pension benefits took effect has left the department short-staffed at a critical juncture in its efforts to reduce crime.

Officers have complained for months that the patrol division is not fully staffed, a contention that department commanders had called untrue. But for the first time, the city's police commissioner is now warning that "staffing is a huge problem" and that shortages could risk breaking momentum in curtailing homicides, shootings and other crime.

A police spokesman said 42 officers left in June, far more than the 17 who departed in the same month in 2009 and the 20 in June 2008. The department is 106 officers shy of a full complement of 3,119 sworn personnel, which includes everyone from beat officers to the senior command staff. There are an additional 53 vacancies in civilian positions.

And to save money, the department has cut the number of academy classes from five or six a year to two or three. A class of 40 officers - 25 funded through a federal stimulus grant - graduated last week; another class with 60 people is scheduled to begin Friday; and a third could begin in the fall.

Still, Commissioner Frederick H. Bealefeld III said this week on Maryland Public Television's "Direct Connection" program that his department can't hire fast enough "to keep up with the attrition rate we're seeing now. We're operating at very conservative staffing levels across all the units. The gap is only going to widen."

Changes in the pension system - which strip more money from the paychecks of officers and firefighters - were made necessary by a deficit in the police and fire retirement fund that could have cost the cash-strapped city $65 million. That problem came as the mayor had to close a $121 million budget shortfall by raising taxes and new fees.

The new rules signed into law by Mayor Stephanie Rawlings-Blake gradually increase officers' pension contributions from 6 percent to 10 percent over four years. The law also fixes cost-of-living increases at 1 percent for officers under 65 and 2 percent for those older, instead of tying the payouts to the fund's performance. Over the past 25 years, the annual increase averaged 3.1 percent.

Most controversial is a requirement that officers work 25 years instead of 20 to retire with full benefits. The change not only targets new hires, but also applies to officers who have been in the department 15 or fewer years. Baltimore County also recently upped its retirement service years to 25, but didn't make the change retroactive.

Union officials have filed a federal lawsuit accusing the city of purposely underfunding the pension system and arguing that the changes violate contractual labor agreements. Those officials had warned that the pension changes would drive officers to leave the department.

And Bealefeld repeatedly warned City Council members that any cuts to his budget would set the department back at least a decade in its crime-fighting efforts. Department officials say homicides and other crimes are at historic lows, and Bealefeld has repeatedly praised his officers for reducing crime while working with fewer resources and less money.

Police spokesman Anthony Guglielmi said it is impossible to determine how many officers left because of pension concerns. He said that the attrition rate for the year so far is "slightly above average," but he also noted that June is typically the month with the most resignations and retirements.

For example, 31 officers left in June 2004, 53 in 2005 and 41 in 2007. The spokesman said that more officers are retiring this year than resigning, a reversal of what happened last year, when more officers quit.

Guglielmi said commanders are developing plans to bolster recruiting amid what he called "fierce competition for law enforcement jobs," including a plan to partner with the military and an initiative to find more female recruits. The mayor's office said city officials will be announcing a hiring initiative in the next few days.

Meanwhile, Guglielmi said, "It's not a question that we're doing more with less. And there is no question that we're going to maintain the level of public safety that we have in years past. We're not going to put a price tag on public safety."

But, the spokesman warned, "We just can't sustain any more cuts."

The depletions most acutely hit the patrol bureau, typically made up of the youngest officers, who are also the ones who interact most with the public and answer tens of thousands of emergency calls each year.

The president of the police union, Robert F. Cherry, said district commanders are turning to overtime to fill patrol cars. He said a midnight shift this week in the Northern District was short five officers.

"We can only cut so much in a town that still needs a lot of work on crime," Cherry said. "We're in danger of sliding back down that path of mediocrity."

Several seasoned city police veterans are among the recently departed. They include Lt. Vernell Shaheed, who was instrumental in a domestic violence unit that followed up on complaints to prevent further violence; Lt. Paul Blair, the former union chief; Detective Darryl Massey, who spent 30 years on the force and was one of its most experienced homicide detectives; and Maj. Scott Bloodsworth, who commanded the Southern District and retired when he objected to being transferred to headquarters.

Police departments throughout the region are hiring. And many prefer to hire officers from other jurisdictions because they get experience without the expense of training. Suburban agencies typically pay better than the city and are less dangerous places to work.

Representatives for the police union complained that the pension cutbacks would put city police at a disadvantage over their suburban counterparts in pay and benefits, hurting not just efforts to hire new officers, but also forcing many to retire early in order to cash in after 20 years on the force.

The 1,600-member Baltimore Fire Department has not yet had an exodus, according to union officials, who said it's harder for firefighters to find jobs. Most departments don't typically do what are called "lateral hires," which makes jumping from one department to another more difficult.

Still, Bob Sledgeski, the president of the firefighters union, said many of his members have gone to Montgomery, Prince George's and Howard counties to take exams.. "Our problems, unlike police, appear to be delayed, but people are going out in droves and testing in other departments," he said.

Compounding the problem, Sledgeski said, is that the city is down about 70 paramedics; he said the department is budgeted for a little more than 200 but has about 130. "And nobody's applying," the union chief said, explaining that a training class in progress now has only a dozen recruits.

"As quick as we're hiring 12, we're losing them," he said.

The day after the pension law took effect, the police and fire unions protested outside a political fundraiser for City Councilman William H. Cole IV, who helped craft the bill. They held signs saying "City Hall Has Turned Their Backs on Police and Firefighters" and "We Protect You. Help Protect Us."

Cherry said he finds it disingenuous that Rawlings-Blake "is quick to tout the reductions in crime" but not "reward the officers who made those numbers a reality."

But the mayor's spokesman, Ryan O'Doherty, said Rawlings-Blake "worked hard in the most serious budget crisis of this city's modern history to make sure that every single police officer remained on the job. There was a possibility ... that police officers could've been laid off."