Engine 15, what's your location?" It is the toneless, relentless voice of headquarters on the radio. In the jump seat of the fire engine, the men, just returning from a fire groan. They know a new assignment is coming.

"Entering headquarters," replies the sergeant, Louis Lozupone.

Just what headquarters wanted to hear. Out spews and assignment for a car accident on the Southwest Freeway. Out of the fire engine tumble five fire-fighters.

Quickly, they pile into a camper-like rescue squad vehicle parked nearby. It and they are off into the Anacostia night, sirens shrieking, only 10 seconds later.

The timing is not always so neat, but the quick shift from fire engine to rescue squad is a common sight in Anacostia and in two neighborhoods in Northwest.

Firehouses in these areas are the homes of "combination squads," or groups of five men who must run both an engine and a rescue squad. There are three such squads in the city. They were formed 17 months ago after the D.C. Fire Department's budget was cut by $1.3 million.

Combination squads replaced a system of closing four fire houses around the city on a rotating basis. That system was scrapped after two children were killed in a September, 1976, fire in Northeast Washington. They lived three blocks from a firehouse that was closed that day.

Obviously, a combination squad cannot be in two places at once. so if the five crewmen are off at an emergency in one vehicle, the other just sits in the station.

If the five men are at an emergency, and another arises for which the five men would be wanted in their "other" vehicle, headquarters does one of two things. They either send another unit from elsewhere, or they wait until the combination squad can return to base and make the swap from one vehicle to the other.

In either case, there is a delay, although it is seldom more than three minutes, according to fire department officials. But even that much time can be too much, the officials said.

Last December, two women were killed in a Northwest Washington townhouse fire. A combination squad responded to the blaze as a rescue squad, and an engine company was dispatched from elsewhere. Firemen's union officials charged that the delay in the arrival of the engine company may have contributed to the deaths of the women, although many fire officials disagreed.

Last week, the combination squad assigned to 2101 14th St. SE. in Anacostia was just finishing up a fire, as Engine Company 15. The men were ordered to return to the station as soon as possible so they could immediately leave again as Rescue Squad 3.

The rescue call was for achild choking. The delay was about three minutes.

Luckily, there was no child and no choking. But as Don Derner, aide to the battalion chief at the Anacostia station, put it: "What if there had been?

"They're playing with people's lives," Derner said.

Nowhere is the playing less frolicsome than in Anacostia.

Only six of the city's 29 engine companies, and only one of its four rescue squads, ae stationed east of the Anacostia River. That area is 40 percent of the city's acreage. More than 40 percent of the city's population lives there.

In addition, the one combination squad in Anacostia has longer average distances to travel on each call than any other in the city, and its monthly average of calls (between 2500 and 300) is one of the highest in the city.

So to spend a Friday and Saturday night with Engine 15 and Rescue Squad 3 is to see two things: what happens under the combination squad arrangement - and what could.

In two nights, between 4 p.m. and 1 a.m., Engine 15-Rescue Squad 3 had a total of nine runs.

Four were for minor fires. One was for a broken water pipe. One was the automobile accident. One was for an unconscious teen-ager. One was an accidental alarm (a citizen thought truck exhaust was a fire).

The ninth call was a minor fire, too. A fuse in a basement clothes dryer began smoking. It was a simple matter. Except that the call for a rescue squad came as RS-3 was crossing Capitol Hill, having just deposited three car crash victims at Rogers Memorial Hospital. The new emergency - not known at first to be a mere clothes dryer problem - was on Southern Avenue SE, more than seven miles away.

Because RS-3 was out of the station, Engine 15 was automatically grounded. Another engine company was dispatched to Souther Avenue.

It took that engine company six minutes to reach the scene and report that the incident was minor. Rescue Squad 3 never made it. Although it was barreling down I-295 at 70 miles an hour, it was still four minutes away when the no-injuries report came over the radio. Unneeded, it slowed down, turned around and returned to base.

Rescue Squad 3's response to the car accident earlier illustrated another difficulty under the combination squad system.

The fire department's 11 ambulances routinely ferry sick and injured people to hospitals, and are well-equipped for that job. Rescue squads are used for actual rescues - freeing people from stalled elevators, breaking down doors, prying open crushed cars and the like.

But from time to time, the ambulances are all otherwise occupied, and rescue squads have to serve as ambulances, even though they are poorly equipped for the task. Such was the case with RS-3 and its car crash.

Three people injured in the crash were carried to the hospital in a cramped, unventilated cabin, along with three firemen, three observers and tons of bulky rescue equipment.

One accident victim, who appeared to be in shock and who complained of a neck injury, had to lie on a foam-rubber mat two feet wide and two inches thick. The rescue squad carrid no pillows or medication, and no blood, glucose or facilities to administer them.

In all, RS-3 was "out of service" on the car crash for 35 minutes. As a result, of necessity, Engine 15 was, too.

Fire department morale has been harmed by the combination squad system, according to the men of Engine 15.

Not only do the men feel the public is protected slightly less well because of it, but they feel their time is sometimes misused. They especially resent having to act as ambulance attendants.

Just after RS-3 had brought its car crash victims to Rogers Memorial Hospital, Gary manders, a crewman, put his hand on the hood of a Fire Department ambulance parked in the receiving area.

"Feel the hood of this ambulance," he said. "It's so hot it'll burn your skin off."

The hood was ice cold, indicating to Manders that the crew had "probably been here drinking coffee for half an hour."

According to fire department records, they had been thre only 14 minutes at the time. But Manders' suspicion was typical of his squad's.

"We don't say do away with the combination squads because it's not up to us to say that," said chief's aide Don Derner. "But it's my personal feeling that you don't cut the fire department budget. Not ever. or else you're forced into something like this."

Deputy Fire Chief James H. Lambert acknowledged that the combination squad system is "not perfect," but he said it "has worked pretty well.

"I would characterize it as the best solution to the problem," Lambert said, referring to the department's budget cut. "We could have just cut two squads out, period. We decided there wasn't any great loss of (response) time (under combination squads)."

Lambert said the department has no plans to scrap or change the system. He acknowledged a morale problem among his men, "because they'd all rather have one squad." But he characterized the problem as small. "The men do good work," he said.

City Councilman David Clarke, chairman of the council committee that oversees the fire department, said he sees "no great inadequacy" in the combination squad system. he said he has received "no tremendous number of complaints . . . I trust the fire department's assessment as to which system is better."

Clarke said that, orginally, his "only concern was down in Southeast," the area covered by Engine 15-Rescue Squad 3, because of the greater distances that unit must travel. But no dangers or delays "of any magnitude have been brought to our attention," Clarke said.