A group of senior citizens and the Fairfax County Fire Department may be preparing for a political battle.

The prize is a coveted mobile medical unit -- a vehicle credited with saving up to 40 percent more lives in medical emergencies than a conventional ambulance.

On one side of the battle line are the elderly residents of Evergreen House, determined to stop the Fairfax County Fire Department from moving the prize from a fire station 2,000 feet from their home to a station almost four miles away.

On the other side is the fire department, trying to solve the jigsaw puzzle that will give more county residents greater access to the Medic unit.

In the middle, and controlling the artillery, is the county Board of Supervisors with the power to settle the dispute.

The mobile medical unit in dispute has been stationed at Annandale Volunteer Fire Department No. 8, just off Columbia Pike, since the Evergreen House for the elderly opened in March 1978. In those 3 1/2 years, the fire station has answered 164 calls at Evergreen House for everything from heart failure to broken hips. And since then, the men and women at the home have contributed to the operation of the station with bingo fund-raisers and hours of volunteer work.

The eight emergency medical units in full operation scattered throughout Fairfax County are equipped with sophisticated monitoring equipment that allows a physician to observe a patient's vital signs by radio from a hospital and relay instructions to cardiac care technicians on the scene.

"The medic units bring the emergency room to the patient," says Capt. Douglas Casey, a spokesman for the rescue services division. "By comparison, the traditional ambulance is little more than a fast taxicab to get the patient to the hospital."

Fire officials have proposed transferring the Annandale unit to the Guinea Road fire station 3.8 miles away from Evergreen House. That would mean the closest medic unit serving Evergreen would be at the Bailey's Crossroads Station, 2.7 miles away.

Fire officials say the distance would mean a difference of less than two minutes in answering calls at Evergreen. And the residents still would have access to the other medical services provided by the neighboring Annandale station.

It's all part of a reshuffling plan designed to provide about 98 percent of the county's population with coverage by the mobile intensive care units, according to Chief Richard Steinberg. The move would not take place until the Franconia fire station puts its medic unit into service later in the year.

If the Annandale unit isn't moved, a small but densely populated section of the county would receive overlapping coverage from three stations while almost a fourth of the county would be getting no service, Steinberg said.

But residents of Evergreen House say they should have priority in keeping a unit at the nearby Annandale Fire Station.

"There is a high concentration of elderly people in this area," notes Jan Brown, manager of the Evergreen House, which has 260 residents. "And older people have a greater need for emergency medical services than other people."

More than 100 Evergreen residents met with county supervisors and fire department officials last week to voice their protests over moving the medic unit.

"We helped pay for that medic unit based on donations," declared Bill Clay, president of the senior citizens' club at Evergreen, at the meeting. "We're paying for it and you want to move it out of our area -- that just doesn't seem fair."

But the funds provided through donations supply only a fraction of the cost of operating the expensive unit, according to Steinberg. Donations helped pay the original $68,000 purchase price of the vehicle. But the bill for operating and staffing the unit is $250,000 annually -- most of which is financed through the county, Steinberg said.

At the meeting with Evergreen residents last week, Supervisor Thomas M. Davis III, who represents the Mason District where the apartment building is located, told residents that he will ask his fellow supervisors to appoint a committee of supervisors, fire officials and Evergreen residents to study the problem before a final decision is made.