AT the height of the summer season, just when an ocean dip is most alluring, an environmental group last week released the first-ever national tally of coastal beach closings. It's enough to give pause to would-be bathers.
More than 2,000 closures of United States beaches were recorded in 1991, primarily due to raw human sewage polluting coastal waters, according to data collected by the Natural Resources Defense Council (NRDC), a national environmental advocacy group.
"Beaches that were not closed may be just as polluted [as those closed]," says Sarah Chasis, the NRDC attorney in charge of the report.
The number of closures would probably be higher, she says, because the lack of consistent, frequent water-testing means that beaches may reach pollution levels of high health risk without being discovered.
Even when it is discovered that water quality standards are violated, there are no federal requirements that the public be notified, Ms. Chasis adds. Survey of states
The report, "Testing the Waters: A National Perspective on Beach Closings," found that:
* Ten states - Alabama, Georgia, Louisiana, Mississippi, New Hampshire, North Carolina, Oregon, South Carolina, Texas, and Washington - monitor their beach waters infrequently, if ever.
* Only four states - Connecticut, New Jersey, New York, and Hawaii - monitor the entire length of their coastlines.
* Out of 2,008 beach closures in 1991, 715 occurred along the Connecticut, New York, and New Jersey shorelines and 588 were between Los Angeles and San Diego.
* Only Connecticut, New Jersey, and Delaware consistently close beaches or post advisories every time water-quality standards are violated.
"The large number of states that do not test or close beaches tells us we need national mandates requiring states to do so, to guarantee that Americans are not left to swim at their own risk," says Ms. Chasis.
Those standards, she says, should include nationwide water quality standards, a monitoring system consistent in type frequency, and mandatory public notification when water quality standards are violated.
The NRDC's study stems from the intense interest in beach contamination that started in the summer of 1988, when medical wastes began floating ashore on East Coast and Gulf state beaches.
While that was unusual, the NRDC has found that high bacteria levels in beach water are common. Bacteria believed to cause illnesses comes from raw sewage overflows, overloaded sewage treatment plants, septic tanks, boating wastes, and runoff that becomes poisonous as it washes over rooftops and roads.
Officials at the US Centers for Disease Control say they are not aware of any recorded epidemics linked to ocean beach swimming. Medical authorities don't typically consider common swimming-related illnesses to be life-threatening.
The US Environmental Protection Agency issued beach-water quality standards for states to adopt in 1986, says Stephen Schaub, an EPA senior microbiologist. They don't always meet those standards, he says.
"Up to now there has been no arm-twisting" for states to adopt them, says Mr. Schaub, who is in charge of reevaluating the EPA's beach-water quality standards.
He explains that states' rights issues interfere with uniform standards. The costs of regular, intensive beach testing can be burdensome and in many cases "nobody wants a beach closed if they're economically dependent on it like resort towns," he says. Precautions for bathers
In August, the EPA will begin gathering together officials from federal and state health agencies, beach property owners, and recreational and environmental groups to formulate uniform, mandatory standards that all states might agree to.
In the meantime, the NRDC suggests these precautions for beachgoers:
* Ask local health officials what the current status of beach water is and whether beaches are always closed when bacterial standards are exeeded.
* Choose beaches adjacent to open ocean waters - beaches removed from urban areas generally pose less of a pollution risk than those near developed areas or in enclosed bays and harbors.
* Stay away from beaches with visible discharge pipes. Avoid swimming at urban beaches after a heavy rainfall.