Fairfax County's elaborate and very popular system of public parks, now run by a semiautonomous park authority, may soon be taken over by the county's Board of Supervisors.

The board, which stripped the county's housing authority of much of its independence last year, is hammering out the details of a similar plan to harness the park authority, which has about 1,200 full- and part-time employes. The board is expected to approve a new park authority charter at its next meeting April 7.

The supervisors describe the move as enhancing efficient management and streamlining government. "We're trying to tighten up the management of the park authority," said County Board Chairman John F. Herrity, long a critic of the county's autonomous agencies.

Most of the 10 members on the park authority's board of directors see the impending shift differently. They see a politically driven effort to dictate important decisions to the park authority, whose 342 parks on 14,000 acres are among the most visible public amenities in Fairfax County.

"The reason we've delivered such a nice, balanced park system is that we're outside the realm of politics," said Robert D. Moss, an 11-year park authority board member who became the board's chairman in January. "I definitely think that will change" if the county board subsumes the park authority, he said.

Moreover, park aficionados say, the worst result of a county takeover would be to deprive the park system of the authority as an outspoken, independent advocacy group. "Who's going to fight for parks against roads and schools and whatever else unless we have a measure of independence?" asked Ellamae S. Doyle, an active park system supporter who has promoted park bond issues at referendums.

Moss, who met this week with two county board members and top Fairfax County officials, said the county seeks to place the park system under the authority of Fairfax County Executive J. Hamilton Lambert, the county board's top appointee. Lambert would be empowered to determine priorities, let contracts, approve projects and control personnel for the park system. The park authority's governing board would assume an advisory role to the Board of Supervisors.

Under the current arrangement, the supervisors already control the half of the park authority's $15.3 million operating budget that comes from the county's general fund; the other half comes from fees paid by users of the park facilities. The county board also reviews the park authority's capital projects.

"Even now they don't have that much independent authority," said Supervisor Thomas M. Davis III.

The park system, which has a strong constituency of young adults, senior citizens, recreational groups and athletic organizations, has been very successful in promoting park bonds at referendums. The last three bond proposals passed handily, including the last one in 1982, for $58 million.

The park system was so popular that it spawned its own citizens force, a self-styled lobbying organization called The Green Team. The group marshaled grass-roots support for the bond issues precinct-by-precinct, in the manner of a political party, and dissuaded politicians who voiced private doubts from speaking publicly against the bond proposals.

The system boasts a diversity of facilities, from the 1,260-acre Huntley Meadows, one of the region's largest wetland areas, to the Wakefield Recreation Center in Annandale, which has a 50-meter pool, six racquetball and squash courts, a gymnasium, photo lab, snack bar, game room, weight room, dance studio and classrooms.

Two years ago, the Fairfax County park authority won a gold medal for excellence in management at the National Recreation and Park Association Conference. The next year the authority won an award for organization from the National Association of Counties.

Nonetheless, critics of the park authority cite a number of grievances that they say justify a change in top-level management.

Two years ago, the county was forced to pay more than $350,000 in settlement costs and legal fees to a contractor who sued the park authority, alleging that it violated bidding and purchasing procedures in selecting a builder for the Pinecrest golf course in Annandale.

More recently, the park authority's attorney, Harry P. (Bud) Hart, angered county board members by representing a developer in a lawsuit against Fairfax County. Although the suit was dismissed and the county prevailed, it left some county politicians uneasy. Hart did not return a reporter's calls.

County politicians also have complained the park authority has been slow to launch new recreation centers and expand old ones -- political plums the supervisors are eager to have in place by the 1987 elections -- even though the funds have been available more than two years..

Park officials acknowledge they have blundered occasionally, but insist that is no reason for the county to deny its current prerogatives.

Park authority Chairman Moss said that the park authority is scheduling community meetings to gather support to fight the county's plans, and that it may seek an opinion from the state attorney general.