Fairfax City's 113 firefighters are battling more than fires these days. They've turned on each other and it's become a year-long, six-alarm fight.

On one side are the 74 active members of the city's 50-year-old volunteer fire department. On the other is the 39-member paid force created last year by City Manager George E. Hubler Jr., a man the volunteers say is determined to "run us out of town" and eliminate a firefighting system built on free labor.

"If Hubler can put on his resume how he took a little podunk town and got rid of its beer-drinking, checkerplaying, redneck volunteer force for an effective, modern, paid force, then the next place that is reviewing his application is going to think he knows what he's doing.... He's terribly ambitious, but he doesn't know a damn thing about running a fire department," said volunteer President Al Adams.

Paid firefighters, said Matt Hughs, a spokesman for the volunteer department, have stuffed the volunteers' pockets with fishhooks and written obscenities on their helmets, cursed and avoided them, even barred them from eating at the station - formerly an accepted practice - unless they sign up for meals days in advance.

Hubler declines to comment on the turmoil, which is similar to that experienced in other growing areas where officials have encouraged obstacles when they try to combine tradition-bound volunteer departments with paid ones.

Volunteers and paid firefighters have been embroiled in controversies periodically in recent years in Washington's Maryland suburbs. Recently, the Montgomery County Council gave preliminary approval to legislation that would centralize the services of the county's 18 volunteer departments, making more use of paid personnel and relieving the volunteers of their long-enjoyed autonomy.

While refusing to comment on the allegations of harassment in Fairfax City, Joseph R. Gebauer, director of the city's fire and rescue services, said some conflicts have been inevitable but the city has to give priority to its fulltime, paid force. "Any time you have two different factions, you're going to have some difficulty," he said.

The difficulty began in May 1978, when Hubler organized a Department of Fire and Rescue Services to augment the volunteer department.

Until then, the volunteers, who own all the city's firefighting equipment and one of its two fire houses, were in complete control.

Under the new system, the volunteers share authority with the new, paid department.

Hubler's ultimate goal, as percieved by volunteers spokesman Adams, is an all-paid force.

Although no major problems have arisen in handling emergency calls, Adams said, Hubler's approach is causing an "uncooperative and potentially dangerous situation."

Harassment has led to a 30 percent drop in volunteer participation on fire and rescue calls, according to volunteers spokesman Hughs, and as a result the department's level of efficiency has declined.

"Sometimes an ambulance or an engine has to be left idle," said Hughs, Why should we have to call another city or town for additional support when we have all the equipment right here?"

City Council member William Scott says Hubler's actions have "slowly eroded the power given to the volunteers in their original charter. He has seen to it that the volunteer chief has no administrative say and that everyone in the department, both paid and volunteer, has to answer to him. I think he's looking to put a feather in his cap."

Council member Carl Hemmer said Hubler has just been doing his job. "He has made judgment calls," he said, "but when there are differing opinions and only one course of action to be followedone is ready to tolerate the pranks and harassment," Hemmer said, "but we can make things better."