In a major reassessment of the health of U.S. coastal waters, federal scientists reported yesterday that overall the nation's marine environment may be less polluted now than a decade ago.

Contrary to the popular belief that the nation's waters grow more polluted each year, scientists monitoring toxic compounds and trace metals in fish livers and shellfish guts conclude that environmental efforts are paying off and chemical contamination on average appears to be either stable or decreasing.

"There are local problems. There are still big problems. But it appears the situation is improving or at least not getting worse," said Thomas O'Connor, manager of the program at the National Oceanic and Atmospheric Administration, which released its results yesterday.

"It's good news. If the data are accurate, this is a really hopeful sign," said Elliott Norse, a marine ecologist and chief scientist at the Center for Marine Conservation, an environmental advocacy group here. "I say three cheers."

Norse, however, said that despite some gains, the United States still has a large marine pollution problem. Moreover, the federal scientists caution that there are still high levels of chemical contaminants in the harbors and bays of Baltimore, Boston, New York, San Diego, Los Angeles and Seattle.

For example, while most of the Chesapeake Bay failed to show worrisome levels of contamination, Baltimore Harbor still shows high concentrations of lead and other trace metals, as well as the remnants of pesticides and fuel burning.

Yet the study suggests that the lawsuits, legislation, hard work and money spent in the 1970s began to show positive results in the marine environment during the 1980s.

"It is quite obvious that the decrease in chemicals in the environment is due to the banning of those chemicals," O'Connor said.

O'Connor and his colleagues saw less evidence of banned or restricted substances such as the pesticides DDT and chlordane. They also saw less polychlorinated biphenyls, or PCBs, which were used in electrical transformers and capacitors.

Lead levels also dropped, almost certainly due to the phasing out of leaded gasoline. In 50 "Mussel Watch" sites visited in the 1970s and 1980s, 39 showed lower concentrations of lead. Cadmium levels also dropped, while copper levels increased. (Of the 11 contaminants examined, copper is the only one whose industrial use has increased.)

Federal scientists stress that their studies did not focus on levels of bacteria in the water or the effects of even low levels of pollutants on human health, nor did they examine the effects of urban and agricultural runoff.

"While these new findings suggest some improvement in the health of the marine environment, the prognosis isn't all good," said Charles Ehler, director of NOAA's Office of Oceanography and Marine Assessment. "Measurements of chemical contaminants alone aren't adequate to determine the overall health of our coastal areas."

Peter Montague, a senior research analyst in the toxics program at Greenpeace, said any optimism over coastal improvements should be tempered by the fact that the study did not examine the health effects of eating fish that harbor small amounts of toxic compounds or trace metals.

The federal study focused only on chemical contaminants found in sediments, the livers of bottom-feeding fish and the soft tissue of mussels and oysters at 287 coastal and estuarial sites around the country.

The samples were collected over the past six years and, in some cases, compared with mussels and oysters sampled at the same sites by the Environmental Protection Agency in the mid-1970s. Mussels and oysters are good sentinels, since they stay in one place and absorb what passes through their systems.

The program sampled sediment and oysters from "representative" sites, and it deliberately avoided obvious "hot spots" such as the highly polluted Houston Ship Channel, the Arthur Kill in New York or the Chelsea River mouth in Boston. The researchers said that these spots already are being monitored for compliance with federal regulations and, though highly polluted, do not offer much insight into the health of larger bodies of water. However, even though the Houston Ship Channel was avoided, seven other sites nearby in Galveston Bay were monitored.

The work reported yesterday follows a report by a group of international ocean experts assembled by the United Nations, who concluded in 1989 that the world's open oceans are relatively clean.

However, there is growing concern that the Third World is increasing its use of pesticides and PCBs, according to Ed Goldberg, an ocean chemist and an author of the U.N. report at the Scripps Institution of Oceanography. An international "Mussel Watch" program is in the works.END NOTES