The Georgia Supreme Court heard arguments Monday in a case that could determine development along the state's 100-mile coastline for generations.

The question the court is expected to answer is whether the 1970 Coastal Marshlands Protection Act requires the state to regulate the way land is developed behind marinas, community docks and bridges. This is the first time the state's highest court will rule on the state law many environmentalists laud as Georgia's most visionary environmental protection.

Center for a Sustainable Coast vs. Coastal Marshlands Protection Committee pits Georgia and an Atlanta developer against several environmental groups. The state and the developer, Atlantan J. Robert Ward, argued that the state's power does not extend beyond the proposed marinas and community docks at Cumberland Harbour, a 1,085-house residential resort near the town of St. Marys.

The community, under construction on a peninsula surrounded mostly by tidal marshes, is in sight of the Cumberland Island National Seashore. Lots are being sold for $150,000 to $750,000. Forty houses have been built and 925 sites have been sold, the developer said.

Michael Landrum of Alpharetta, an early buyer in 2002, has been waiting to build on his lot until the case is resolved. He expected the marinas and docks to be under construction by now.

"We wouldn't have wanted to buy into a place that was going to let development destroy the natural beauty," Landrum said.

The lawsuit challenges a state permit issued to the developer in March 2005 that would allow more than 800 boats of all sizes in wet slips and dry dock storage in two marinas. It would be the largest marina complex on the Georgia coast, with 3.2 miles of docks, board walks and slips.

Environmentalists argue the state is obligated to protect the marshes from polluted runoff created by the houses, streets and other development around marinas and docks. They want the state to require the developer to prohibit any structures near the marsh and to filter, clean and reduce storm water runoff discharged into the marsh.

At stake, they say, are Georgia's 382,000 acres of tidal marshes. The protective ribbon of sinewy gray-green grass outlining estuaries and tidal rivers is the nursery for crab, shrimp and some fish species.

The court has until the end of November to rule.

On Monday, the justices did not indicate how they might decide.

In their court filing, the environmentalists likened the state-owned marshlands to a state park and said the state "must balance the use of state-owned marshes for private benefit against the public's interest in its property."

An attorney for Ward, the developer who owns Point Peter LLP and Orlando-based Land Resource, argued he is already doing more than state and local laws require by leaving a 35-foot natural buffer between the marsh and construction instead of 25 feet. The development also has several storm-water ponds for collection.

Also, to protect the marshes, only 92 of a possible 300 private docks will be built, said the developer.

Will Hurst, spokesman for Land Resource, said it's in the developer's interest to protect the marsh. "That's what we're selling access to. . . vast marshes overlooking Cumberland Island," he said.