Nine months after the cancer-causing chemical ethylene dibromide (EDB) was banned for most agricultural uses, the Environmental Protection Agency has proposed for the first time to list it as a hazardous waste.

The agency said it took the step after finding that waste water and other residues from the production of EDB contained the chemical "in concentrations of up to 75 percent." Because the chemical is not currently classified as hazardous, chemical manufacturers can legally dispose of such wastes in unlined pits where the highly soluble chemical can spread through ground water.

EPA officials said the chemical has been discovered in ground water under the Occidental Chemical Co. plant in Lathrop, Calif., and the Great Lakes Chemical Corp. in El Dorado, Ariz. Both manufacture EDB or use it in the production of other chemicals.

EDB, once a popular pesticide used to fumigate soil, stored grains and fruit, was banned for most agricultural uses after the EPA discovered that it had contaminated hundreds of wells and a wide variety of food products.

However, nearly 90 percent of all EDB goes into gasoline as an anti-knock additive, which is still a legal use. EDB also is used as a solvent for resins and waxes, and is generated as a waste in the production of some other chemicals. According to EPA figures, chemical firms are generating at least 26,000 tons of EDB-contaminated wastewater and 143 tons of solid wastes each year.

An EPA spokesman said the agency believes that most of that waste is being disposed of by injection into deep wells, but he could not be more specific. "Companies consider what they do with their waste to be confidential information," he said.