The number of D.C. police officers in the District has fallen below 3,800, its lowest level in a decade, breaking a threshold that top District officials once warned would be dangerously thin in a city that continues to grow.

As of Dec. 17, D.C. police had 3,786 officers, according to the mayor’s office, falling from more than 3,929 a year ago. Meanwhile this year, homicides across the District have surged more than 50 percent, and a spike in robberies in some neighborhoods instilled renewed fear of a return to the higher crime rates of the 1990s. Though police say violent crime is at its lowest level in seven years, residents polled put crime at the top of their worries this year.

District police say that they have been unable to keep up with attrition triggered by the retirements of officers who joined the force during a hiring binge in 1989 and 1990. From January 2014 through October, the department lost 764 officers — more than half through retirement — and hired 562.

[Wave of police retirements could shrink force]

D.C. Police Chief Cathy L. Lanier did not respond to a request for an interview. But in her last budget memo to the D.C. Council, the chief said that by the end of this year more than half of the command staff, one-third of all lieutenants and detectives and nearly one-third of all sergeants would be eligible to retire. She wrote in a letter to residents posted on the Internet that the departures “present a challenge.”

Kevin Donahue, the deputy mayor for public safety, said the District is not in a crisis and in fact had long planned for the retirement bubble to burst. “Our focus has been less on the golden number, but on working within the resources we have to try and have the most efficient and effective force,” he said.

District officials blame the staffing shortfall almost entirely on retirements, saying attrition rates for officers who leave for other reasons have remained constant for the past decade. But the union representing the rank and file says that the exodus also includes officers and street-level supervisors who are leaving with fewer than 10 years on the force. The union argues that this is evidence officers are fleeing a department and a chief they do not like, as well as a crime plan they say will not make the District safer.

[District’s population continues to grow]

“The only way to stop the hemorrhaging of personnel on this department is to fundamentally change the way it is managed,” Gregg Pemberton, the police union’s treasurer, wrote in a letter to residents posted on the Internet, saying officers are leaving because of erratic scheduling, pay that is not competitive and ineffectual deployment strategies.

Lanier countered with her own Internet bulletin, titled, “Setting the record straight,” saying that most of the departures were anticipated retirements while outlining her strategies for hiring more civilians to push sworn officers out of desk jobs and back onto the streets, implementing new technology to speed up administrative functions and developing incentives to persuade other officers to stay.

Lanier noted that the violent crime rate is at its lowest level since 2007 and has dropped 15 percent between 2009 and 2014. During that same period, the District’s population has grown 10 percent. The chief said serious crime is down 5 percent this year, including sexual assaults and assaults with dangerous weapons, even with the rise in homicides.

In 2011, Lanier warned of trouble if department staffing fell below 3,800, and a year later she told WTOP-FM (103.5) that should the department break that barrier, it would be “harder for me to do what I have to do. I have to be creative, and sacrifice things to make up for other things.”

[How many police the District needs depends on whom you ask]

Lanier’s letter to residents did not address specific complaints about the impact of low staffing that the police union raised in its memo.

The labor group said that it can take hours for a crime-lab technician to respond to a burglary to dust for fingerprints, and officers trained to confront active shooters must work overtime to ensure adequate coverage. Officers interviewed said that they spend shifts racing from call to call, spending less time in the neighborhoods to which they are assigned.

“I tell people the truth,” said 23-year veteran Officer Nicholas Deciutiis , who is assigned to the First District, which includes Capitol Hill, and is a union shop steward. “We do the best we can out here with what we have.”

The police union says that the practice of temporarily pulling detectives and others who work behind the scenes into street duty, called “high visibility patrols,” gives residents a false impression that the department is flooded with officers. Meanwhile, the union says, burglary and other investigations slow or stall. The depleted force, the union said in its letter, “is causing innumerable problems and complications in our ability to keep the streets safe.”

Benjamin Fetting, a master patrol officer in the Third District, which includes Dupont Circle, Adams Morgan, Kalorama and ­Columbia Heights, said: “We do more with less every day.” The union shop steward said that it is not uncommon for an officer talking with a crime victim to race off to a more urgent call: “We spend more time running around the District instead of spending quality time in our [patrol area].”

He said that any special event, large protest or holiday can cause crippling staff shortages. “We’re starting to feel the pain,” said Fetting, who is trained to use assault weapons and is on an active shooting team. He said that, to keep a sufficient number of teams on the streets, he has needed to work overtime.

The District, with a population of about 672,000, has more than five police officers for every 1,000 residents.

That is one of the highest police staffing levels per capita of any city in the country, exceeding a Justice Department recommendation of two officers for every 1,000 people. Most large cities pass that threshold, including Baltimore, Chicago, Philadelphia, New York, St. Louis and Atlanta.

D.C. officials have long argued that the city’s unique status as the nation’s capital, home of the president and a terrorism target, requires a large police force.

They also note that the District’s population can more than double during the workday as commuters and tourists fill up the Mall and other attractions. Various officials over the years have put the number of officers the District needs at anywhere between 3,600 and 4,200.

D.C. Council Chairman Phil Mendelson (D) said that there is no personnel crisis. He said discussion four years ago over the 3,800 number was born out of “crisis of the moment” but does not necessarily reflect the city today.

Said Mendelson, who once chaired the council’s public safety committee: “I personally think it would be helpful if the staffing of police were larger.” He added, “At the same time, I really do not think the attrition we’re seeing now is surprising and should set off alarms.”

Mendelson noted a push for civilians to replace desk-bound officers and said that the problem with the amount of crime-scene technicians — a job slowly transitioning from sworn officers to civilians — is being addressed with more hires. “The bottom line for me is, can residents continue to feel safe?” he said, adding that “3,800 is not a magic number.”

Lanier, in her letter, said new funding authorized by the council and mayor means that civilians soon can replace 75 officers now assigned to the forensic science building.

Police also point to several successes in the crime fight, including arrests in several spates of street robberies on Capitol Hill and apprehending two suspects in holdups of multiple taxi drivers. Earlier this month, Lanier announced arrests in 12 homicide cases. She said staffing in the homicide unit never dropped.

Donahue would not say how large a police force Mayor Muriel E. Bowser (D) thinks is needed. But he said the mayor is authorizing overtime and working to civilianize positions faster — devoting $2.9 million to 48 new positions — and is implementing a $2.5 million officer incentive program “to try to slow the pace of attrition.”