NEW YORK, SEPT. 6 -- Tests performed on a sample of ash from the garbage hauled 6,000 miles at sea on a barge showed levels of toxins exceeding federal limits for the underground disposal of industrial waste, Newsday reported today.

Town officials in Islip, where half the garbage was produced, plan to bury the ash in a Long Island landfill after its incineration is completed, but environmentalists are seeking to block the dumping plan.

The environmentalists, led by the New York Public Interest Research Group (NYPIRG), say results of the toxicity tests commissioned by Newsday support their argument that toxins in the ash could contaminate ground water and endanger the health of residents.

The tests show higher levels of cadmium and lead than federal regulations permit industrial firms to dump in municipal landfills. The ingestion of the toxic substances can cause kidney, lung and other health problems.

Islip officials argue that, because the base of the dump site is lined, burial of the ash presents no health threat despite the toxins. They also contend the dumping was exempt from the federal regulations because the ash was from the burning of municipal garbage, not industrial waste.

But environmentalists say state officials have testified that the landfill, located above Long Island's sole remaining source of fresh drinking water -- the Magothy Aquifer -- is leaking.

NYPIRG lawyer Randall Weiner said his group plans to return to court Tuesday in an effort to extend a court order issued last week that blocked dumping of the ash and expansion of the landfill.

State Appellate Court Justice Stanley Harwood signed the temporary restraining order Thursday barring dumping the ash into the Blydenburgh landfill.

The order, which did not halt the round-the-clock burning of the 3,186 tons of garbage at the Southwest Incinerator in Brooklyn, was the latest setback in the five-month-old effort to dispose of the trash.