Southern Maryland health planners have recommended that the metropolitan area's largest prepaid health plan - Group Health Association - be allowed to start a major new clinic for 27,000 members in the District-Prince George's County border region.

The Southern Maryland Health Systems Agency, four-county medical facility planning body, voted by 13 to 10 to overrule wide opposition by Prince George's County doctors to the Group Health expansion.

The health agency at a meeting Wednesday night also:

Urged by a 19 to 1 vote that state health officials decertify - in effect, kill - a long controversial plan for a new Parkway Hospital in Laurel, four miles from the nearly complete, county-owned Greater Laurel Hospital.

Endorsed a $500,000 grant to a Prince George's doctor's group to help them start a new "independent practice association" - a loosely affiliated group with 200 member doctors who plan to offer prepaid health care to subscribers in competition with the GHA clinic. The association, called Prince George's Health Services, was started with Prince George's County Medical Society help.

GHA has long operated clinics in the District, Rockville, Hyattsville and Annandale."But we have 12,000 Prince George's County members and 15,000 District members in the same are who've had to travel to downtown Washington for their care," said Thomas Chapman, GHA's assistant executive director.

"We hope to occupy the new clinic, on Auth Road off Branch Avenue in Camp Springs, next year."

It will be built by a private builder and leased to GHA for $453,000 a year, GHA said. But state health officials must still approve all the Southern Maryland agency's decisions.

The decision on Parkway Hospital is the latest in a five-year battle over building first a privately owned, then a non-profit hospital on a site owned by the project's founder, Dr. J. Allan Offen. Offen said he would donate the site for non-profit operation.