The District is on the cusp of a severe shortage of police officers as a potential flood of retirements and the departures of some young officers threaten to shrink the force even as the city grows and 911 calls increase.

The expected shortages are being driven by hundreds of police officers who joined the force amid a hiring binge 25 years ago and are at or near retirement age. Meanwhile, younger officers say they are leaving for better pay with suburban police departments or have become fed up with city bureaucracy.

The emerging trends have alarmed D.C. Police Chief Cathy L. Lanier and several D.C. Council members, who said that the shortages could tax a department already scrambling to keep up with the District’s new and bursting nightlife and redeveloped neighborhoods. The D.C. police department is just shy of 4,000 officers, and Lanier has warned that her force can’t get much smaller.

“We’re going to fall behind,” the chief said of the personnel shifts. She said she is hiring 300 officers a year — the maximum she can with her budget, training resources and ability to conduct background checks on candidates.

“I can’t compromise standards,” said Lanier, who also acknowledged that the department has told several officers they had to leave because they had reached mandatory retirement age, a rule that had been long overlooked but is now being enforced.

Police union officials said 192 officers left in the first six months of this year, while 209 have been hired. But defections accelerated over the summer: 73 officers left in June and July. In an average month, 15 officers leave the force.

The issue has alarmed some lawmakers. Council member Tommy Wells (D-Ward 6) said he proposed adding $6 million to the police department’s budget to hire more civilians, allowing ­Lanier to push desk-bound officers back on the streets. But the idea was rejected.

Wells, who chairs the council’s Public Safety Committee, said he believes Lanier was “forthright and honest when she asked for help.”

“I believe we need a growing police force,” he said.

Chuck Wexler, executive director of the Police Executive Research Forum, which studies trends in law enforcement, said the District is not alone in struggling both to keep the officers it has and to hire new ones.

He said many departments slowed or stopped hiring late last decade, and some imposed layoffs. Now, with the recession over, “we’re seeing many departments hiring at the same time,” Wexler said. “There is a lot of demand for qualified applicants. For every one person you want to hire, you have to look at 10 to 15.”

He noted the downside of hiring too many officers too fast: “You hire a whole bunch at once, they get old at the same time.”

Indeed, the District is faced with the specter of mass retirements largely because of its past hiring practices. D.C. police hired nearly 1,500 officers in 1989 alone, boosting its force by 40 percent in a single year. The Class of 1989 became notorious for the number of officers who got into legal trouble. Now, the hundreds who remain are able to retire at full pension over the next six to 12 months. One estimate by the police union says that as many as 400 officers could put in their papers now and leave.

Even as the District’s population grows, its government is still recovering from leaner times. Overall, the size of the police force has shrunk from 4,040 in 2009 to 3,984 last year, while the city’s population grew about 7 percent. At a D.C. Council committee hearing in May, Lanier warned that “we are still recovering from the disinvestment during the recession.”

And calls to 911 have increased even faster: The city received nearly 20,000 more emergency calls in 2013 than in 2012.

Meanwhile, union officials said the city has a perennial problem with retention: For instance, of 19 officers who graduated from one D.C. police academy class in 2006, only six remain on the force. “We can’t keep the people we’re hiring,” said Delroy Burton, chairman of the police union.

Nathan Guilfoyle was in that D.C. academy class in 2006, and he left for Howard County after two years patrolling part of the District that runs from Adams Morgan to Shaw.

“I liked the work,” Guilfoyle said. “I didn’t like all the politics that come with a city department.”

The 35-year-old is now a decorated corporal in Howard and working as a detective. He is one of 457 officers in an agency a fraction of the size of the one in which he began his career.

Guilfoyle acknowledges that he was lured to the District for the “excitement of the city” but says that faded after he got married and wanted a family.

“The commute made it impossible to see my wife,” Guilfoyle said. “My days off were Tuesday-Wednesday or Wednesday-Thursday.” He now lives with his wife and two children about 20 miles northwest of Ellicott City.

Lanier said young officers often leave because they get homesick or they applied to the District while remaining on waiting lists for hometown departments. She said she knows of one officer who wanted to be an FBI agent and was told to get three to five years’ experience on a local force “and they’d snatch him right up. There’s no place like Washington to get it.”

The chief announced last week that she would continue to periodically assign plainclothes officers to uniformed patrol beats. She said that temporary redeployment might be “more crucial now” that the size of the force is dwindling.

The plan immediately set off alarm bells with the rank and file. The union warned that investigations of such crimes as burglaries would fall behind.

Lanier said each police unit can ask to be exempted, but she added that she would be judicious and would review requests to opt out on a case-by-case basis.

Lanier also said she would consider rehiring some of the 300 civilian workers released from the department over the years. She said 90 officers now doing administrative work could immediately return to the street if she could hire civilian replacements.

But some are challenging ­Lanier’s efforts to simultaneously push other officers out. The senior police officers who were ordered to retire, for instance, cannot understand why they were forced out at a time when every body counts. Even taking a desk job could free up someone else for the street, they say.

Lanier has said the mandatory retirement age is 60, with waivers allowed up to 64, though she acknowledged that the rules ­haven’t been enforced in many years. The issue surfaced at an individual’s retirement board hearing recently. “It’s in the hiring paperwork,” Lanier said. “It’s not a secret.”

The chief said eight officers were ordered to retire. The union puts the number at 17 and says it is exploring whether to take the issue to court.

Willie Harris, 65, said he found out in a letter that he would have to go by the end of June. He joined the force from the department of corrections, and his 17 years are short of the 25 needed for a full pension. The lifelong District resident, who patrolled some of the city’s most dangerous housing projects, had to move to North Carolina to afford an apartment.

“I got just about every award they could give,” Harris said, noting he spent his entire career in patrol in the 1st Police Distinct.

“I cleaned up the drugs and got the dealers out,” said the former officer, who grew up in Southeast and patrolled Potomac Gardens. “The people who lived where I patrolled had a right to live in a drug-free environment and get the same police services as everyone else. The drug dealers knew we cops worked in shifts, and when I came on, they would leave.”

With him and others gone, Harris said, “I don’t know what they’re going to do.”

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