ANNAPOLIS, SEPT. 5 -- To avoid a widespread embargo of its clams and oysters, Maryland has agreed to ban harvesting around marinas and in 11 small areas of the Chesapeake Bay where high levels of bacteria have been found after heavy rain, a health official said today.

The Interstate Shellfish Sanitation Commission, which establishes public health guidelines for the nation's shellfish industry, had threatened to declare Maryland in violation if it did not limit its clam and oyster harvesting areas by Sept. 15. The move could have led many states to ban the importing of clams and oysters from Maryland.

Crabs are not affected by the ban.

Richard E. Thompson, chairman of the commission, said today that he is satisfied with Maryland's actions. He said state officials made it clear in letters to him that they objected to the new limits, but imposed them to avoid the threat of embargo.

"They say they think they're right, but cannot afford even a hint of a public health problem," he said.

Officials with Maryland's Department of Environment could not be reached for comment today. But last month they said they disagreed with the shellfish commission, which is made up of representatives from 23 shellfish producing states, but would take whatever actions needed to avoid sanctions.

Maryland's annual oyster harvest sells for about $18 million at dockside, while the clam crop sells for about $9 million. But state officials calculate the shellfish are worth three times this amount to the state economy after being processed, shipped and sold in restaurants.

With clammers suffering from a partial embargo imposed by Maine and Massachusetts, and this year's oyster crop ravaged by the disease MSX, Department of Environment spokesman Ray Feldmann said last month, "Anything we can do to protect that industry and to protect the reputation of Maryland, we're going to do."

Under the new Maryland regulations, shellfish harvesting will be banned in 11 areas in southern Maryland and the Eastern Shore for at least four days after each heavy rainfall, when bacteria counts are usually higher than normal. State officials argue that the high counts are caused by agricultural runoff and animal waste, but commission officials have made no determinations.

However, it is expected to take several months for Maryland to design the monitoring program, and the state has banned all shellfish harvesting in these areas until the program is ready.

In addition, the state has agreed to establish a buffer zone around marinas, where pollution is normally heavier than other areas of the bay. The buffer zones extend between 100 and 200 feet beyond the marinas, depending on a marina's size.

Watermen who harvest oysters between September and March have complained bitterly to state officials that the new limits would hurt because they work during the rainiest months. The areas where oyster harvesting is allowed has been limited severely by the sudden spread of MSX, they pointed out.

During the past two years, Maryland has argued before the shellfish commission that its waters are just as healthy as those of other shellfish producing states, but that other states did not do such a good job in measuring water quality.

Thompson acknowledged this, but said, "They {Maryland officials} claim that they went and collected so much data that showed conditions were bad, and if they'd just sampled less we wouldn't have known the problem was there. That's correct, but it doesn't speak to good public health."