The District’s fire chief is moving to have firefighters work shorter but more frequent shifts, a controversial change that he said would encourage firefighters to live closer to the city and lessen costs by cutting as many as 400 positions.

Chief Kenneth B. Ellerbe said the D.C. Department of Fire and Emergency Medical Services is gearing up for a contract battle with the 1,800-member firefighters union. The union wants to retain the current system, under which firefighters work 24-hour shifts followed by three days off.

Ellerbe’s proposal would change the schedule to three 12-hour day shifts on consecutive days, three 12-hour night shifts and then three days off before restarting the cycle.

Through the elimination of overtime costs and workforce attrition that will probably take three or four years, Ellerbe said, the department would eventually save $36 million a year under the proposal. But the union said the new system would cost the District more money and cause personal hardships for many firefighters.

The city’s contract with Local 36 of the International Association of Fire Fighters expired in 2007. Negotiations on a new pact are set to begin soon, Ellerbe said Wednesday at a breakfast attended by Mayor Vincent C. Gray (D) and the D.C. Council.

Edward C. Smith, the union president, said Ellerbe’s proposal would be “devastating” to union members. “Morale, people’s family lives, day care, commuter costs, all sorts of problems,” said Smith, a fire captain.

Ellerbe said the new system would increase the number of days worked by firefighters each month from eight to 22. He also said it would enable the department to recall personnel more quickly during emergencies and reduce the risk of accidents on the job.

“During the second half of a 24-hour shift, mistakes can happen,” the chief said.

Ellerbe said that 25 percent of firefighters live in the city and that 41 percent live 30 to 100 miles away. Others live as far off as New Jersey and the Carolinas, he said.

“That can create a huge challenge for us if we need to recall our whole workforce,” he said, adding that it took “quite a while” for the department to fully mobilize after the terrorist attacks of Sept. 11, 2001.

Many D.C. firefighters like the current system’s three-day block of free time, which allows them to commute great distances and still spend significant time with their families and, in some cases, work other jobs.

Many firefighters in the Maryland and Virginia suburbs also work shifts of 24 hours on duty followed by 72 hours off.

Ellerbe’s proposal will be “a big issue” in upcoming contract negotiations, said Smith, who vowed to fight it vigorously. Many firefighters who depend on incomes from second jobs would have much less time for such work, he said.

“The whole membership is against it,” Smith said of the proposal.

The starting salary for a D.C. firefighter is $44,302, and the base salary for a firefighter with 20 years of experience is $65,568, Smith said. Sergeants, lieutenants and captains are among those represented by the union. The membership’s average salary, not including overtime, is a little more than $67,000, Smith said.

Smith disputed the chief’s assertion that the change in work shifts would help save money by cutting overtime costs. “I have numbers saying it would actually cost the city $16 million,” Smith said.

As for firefighters living in distant places, Smith said, “A lot of my members would love to live in the city.” But living as comfortably in the District as they live in other communities would be too expensive, he said.

Smith said Ellerbe was exaggerating the mobilization issue. In a major disaster, “the command has to set up first, to be ready for the influx of members,” Smith said. “So a reasonable delay in members coming back in is a good thing, to allow the command staff to set up and be able to deploy people appropriately.”

Staff writers Nikita Stewart, Miranda S. Spivack and Victor Zapana contributed to this report.