For as long as anyone can remember, ambulances in the District were staffed two shifts a day, evenly split into 12-hour blocks. But new data suggest that just as with train schedules, there are peak and off-peak hours for sickness and trauma.

D.C. Fire Chief Kenneth B. Ellerbe is proposing adjusting the emergency service timetable, which he says will give people faster and better care when they need it most — between 7 a.m. and 1 a.m.

But the plan involves a controversial element: The chief would pull all 14 advanced life-support paramedic vehicles from the street between 1 a.m. and 7 a.m., saying that the 25 basic life-support ambulances and firefighter-trained paramedics riding on engines can fill the gap.

“We’re trying to redeploy our resources to better serve the city,” Ellerbe said at a news conference Tuesday.

The District has 25 ambulances and 14 advanced life-support paramedic units, staffed by highly trained personnel who can administer drugs, do tracheotomies and utilize electrocardiograms to diagnose heart attacks. Under the proposal, the overnight hours would be staffed by those on the 25 ambulances. Firefighters who are trained as paramedics and seven supervisors can provide advanced care, either from a firetruck or ambulance.

Last year, there were 21,932 people seeking an ambulance in the District who called 911 between 1 and 7 a.m. That represented 15 percent of the total call volume. The highest number of calls — 44,574 — came between 1 and 5 p.m.

Unions representing firefighters and paramedics have reservations about the proposal, with some saying that firefighters who answer medical calls will have to do more work and could be spread thin if they’re busy with a fire. “We’re meeting a higher demand for emergency medical service, but we’re gambling between 1 and 7 a.m.,” said Ed Smith, president of the union that represents D.C. firefighters.

Kenneth Lyons, president of the union for many of the paramedics, defended the proposal.

“We’re not losing the ability to provide advanced life support,” he said. But he also said that the department has between 80 and 100 openings for paramedics. At the news conference, he said the department is “doing the best we can do with the limited resources we have.”

D.C. Council member Phil Mendelson (D), chairman of the Committee of Public Safety and the Judiciary, said he was disappointed with how the proposal, which would require council approval, was communicated to the public

“I don’t want to be defending the plan,” Mendelson said, adding that he has been given only general details. “But as a general proposition, it makes sense that you’d staff according to need. . . . But that’s what the discussion needs to be about.” He said the council has not yet scheduled hearings.

Mendelson said the fire department is approaching 200 vacancies in operations, which includes fire suppression and medical services. He said the chief is plugging holes with overtime, sometimes keeping firefighters and paramedics on double 12- or 24-hour shifts.

Ellerbe’s proposal, Mendelson said, “would help with their overtime problem.”