WASHINGTON — The District of Columbia 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 Police Chief Cathy Lanier and several D.C. Council members, who say 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.