Microscopic organisms that may pose a danger to human health have been discovered by scientists in some oysters and clams taken from commercial shellfishing areas of the Chesapeake Bay, according to an article in the May 6 issue of Science magazine.

In their article, two scientists from the Smithsonian Institution and one from the state of Maryland said that the microorganisms detected in the shellfish belong to three families of microorganisms that have been associated with "serious diseases of humans and domestic animals."

However, both the authors and other scientist contacted about the findings were quick to caution that the organisms discovered may be harmless - benign tenants of the shellfish's system, similar to the bacteria that harmlessly inhabit the human body.

John C. Harshbarger, a microbiologist with the Smithsonian's National Museum of Natural History, and one of the article's authors, said yesterday that "the only thing we know is that we found some groups of organisms in these animals that have been associated with human disease. . .

"At this point we don't have a specific identity" for the individual organisms, he added.

However, in the article Harshbarger and his coauthors noted that, "If verified, these findings may have far-reaching economic and public health significance."

The organisms detected belong to groups known as mycoplasmas, chlamydiae - which Harshbarger said are associated with pneumonia-like diseases - and rickettsiae. Some organisms in the rickettsiae family, Harshbarger said , are known to cause Rocky Mountain spotted fever and typhus.

Samples of the organisms collected during the year-long study by Harshbarger, his colleague Sing Chen Chang, and Sara V. Otto of the Maryland Department of Natural Resources, have been sent to the National Animal Disease Laboratory in Iowa for further testing, Harshbarger said yesterday.

Rita Colwell, a University of Maryland microbiologist contacted yesterday, emphasized that these ongoing tests are essential to allow scientists to make a determination whether the organisms are harmless or harmful either to humans or to the shellfish themselves.

Pointing to the five-long-year decline in the oyster population of the Chesapeake Bay, she said that "if the oysters were taken from an area of suffering a decline . . . there might be an association with the oysters' mortality - these organisms might contribute to the morality."

If the results of the tests going on in Iowa do establish some link between the newly discovered shellfish organisms and some human diseases, the scientists' findings may become the latest in a series of calamities to hit Maryland's multimillion-dollar seafood industry in the last few years.

Just a few months ago, the unusually cold winter laid down a bed of ice on the bay so thick that oystering, the Maryland watermen's main wintertime source of income, became almost impossible for two months.

According to the Smithsonian's Harshbarger, the tests results from Iowa precisely identifying the newly discovered microorganisms should be available in several months.