The National Cancer Institute declares in a report being released today that ethylene dichloride, one of the nation's most heavily used chemicals, has been shown in laboratory tests on animals to produce cancer.

The chemical known as EDC, is a colorless, oily liquid widely used in manufacturing processes including gasoline antiknock additivies, drycleaning compounds, plastics and grain fumigation. Federal researchers estimated about 2 million workers are exposed to EDC and that 163 million pounds of the chemical are accidentally released into the air and water through industrial emissions.

"There's a possibility that people exposed to this chemical run a cancer risk if the exposure is significant," said Dr. Cipriano Cueto, chief of the cancer institute's toxicology branch. Cueto said, however, that the level and duration of the exposure had not yet been determined.

"We don't know whether it would be months or years," he said. "But the weight of the evidence is pretty convincing that we've got a problem."

The institute study, one of about 300 long-term laboratory tests on suspected carcinogens, showed a number of different tumors produced by the chemical in rats and mice.

A spokesman for the Manufacturing Chemists' Association, an industry trade group said yesterday that preliminary, results from its own studies on EDC being conducted in Italy had not yet shown any tumors in laboratory animals.