Days after she acknowledged widespread failure to meet national standards on dispatch times, the director of the District’s 911 center resigned under pressure, according to city officials.

Jennifer A.J. Greene, who rose through the ranks of the D.C. police over three decades and had served as head of the Unified Communications Center since 2011, will leave her post immediately, said Michael Czin, a spokesman for Mayor Muriel E. Bowser (D).

Greene had a rocky tenure that most recently included delays in firefighters responding to a deadly Metro tunnel fire and an incident in which a medic closest to a choking toddler was not dispatched to the scene. The boy later died.

Greene was asked to resign by Bowser’s office, according to two administration officials familiar with the situation. The officials spoke on the condition of anonymity because it is a personnel matter.

During a hearing last week, Greene faced searing criticism from D.C. Council member Kenyan R. McDuffie (D-Ward 5), chairman of the Judiciary Committee, who questioned why average city dispatch times were consistently more than a minute longer than a national standard of 90 seconds for most calls.

“Did you all ever meet that internal one-minute-and-30-second standard?” McDuffie asked.

“No,” Greene said.

“Who set the one-minute-and-30-second internal standard?” McDuffie asked.

“That’s a good question,” Greene replied. “That’s something me and my team have been looking at.”

Greene said the department was looking at changing its internal standard to “something more realistic to shoot for,” she said. “We just haven’t made that standard, so we need to look at it; we’ve been talking about it for over a year.”

Wanda Gattison, a spokeswoman for the 911 agency, said Greene agreed to resign Sunday night. Gattison said Christopher Geldart, the director of the D.C. Homeland Security and Emergency Management Agency, will run the 911 center on an interim basis. Greene made $184,000 a year; her severance package could not immediately be learned.

Greene declined to comment when reached by phone Monday.

The 911 center has been under scrutiny since the Jan. 12 Metro incident near the L’Enfant Plaza station that claimed one woman’s life and left many others trapped in a train as smoke filled the underground tunnel. The National Transportation Safety Board continues to investigate, and Metro and fire officials have come under scrutiny.

Firefighters were hampered by poor radio communications — first responders had to rely on cellphones and hand-carried messages — and Metro and the District have gone back and forth over whether underground relays designed to boost signal strength were properly tested. Metro accused the D.C. fire department of failing to tell transit officials that it changed the way its signals operate.

Greene also was in charge when the fire department implemented a new computer tablet system designed to track fire engines and ambulances and help dispatch the nearest apparatus to emergencies. But the fire union complained about poor training and frequent breakdowns.

Edward C. Smith, president of the D.C. firefighters union, said he was “glad that the mayor has recognized that leadership in the 911 center is an important piece of the puzzle to reassuring public safety.”

Smith said that in meetings that involved Greene, “we felt as though a lot of our concerns fell on deaf ears.”

District officials acknowledged in March that the dispatch system had malfunctioned since it had been installed in the fall and that response times had fallen to their worst levels in two years. The computer system often left dispatchers blind to whether they were sending the closest vehicles to an emergency.

That acknowledgment came after a toddler who choked on grapes in his family’s Northwest Washington home died. Paramedics blocks from the home were not dispatched; the computer instead sent a unit that was about a mile away, and it took seven minutes to arrive.

Officials said that paramedics in the closest unit had not properly logged on, but the fire union said that computer tablets routinely lost their signal as vehicles crossed the District, sometimes giving dispatchers inaccurate information about their location. The tablet system cost $13 million.