A commercial, portable process to destroy highly toxic PCBs onsite is on the verge of winning government permission for marketing, Sunohio Corp.

"If the system will do what the company tells us it will do, it is a very significant breakthrough," said J. William Gunter, leader of the EPA team on PCB regulation.

PCBs, or polychlorinated biphenyls, cause liver and nerve damage in humans and are suspected of causing cancer. Their production was halted in 1977, but an estimated 350,000 tons of contaminated oils still are in use or in storage nationwide, mainly in electrical equipment where they were used as insulation.

PCB disposal has been a major headache for regulators, because only very high temperatures will destroy the compound and citizen groups have strongly opposed most proposed incinerator locations. There are eight landfills nationwide that legally receive PCBs but only in solid form. Two incinerators are in the planning stages in Arkansas and Texas, but the only existing ones belong to a General Electric Co. plant in Waterford, N.Y., and an Eastman Co. plant in Tennessee.

"It's been a huge problem," said Steve Jellinek, EPA's assistant administrator for toxic chemicals. He added that he was very encouraged by the Sunohio procedure and optimistic that it would receive approval.

The company's process uses a commercially available reagent, which was not identified, to strip chlorine atoms from the complex PCB molecule. Trucking the equipment to the sheds and warehouses where old transformers and electrical capacitors are stored, will eliminate the need to transport contaminated oil around the country for treatment or destruction, according to Otis D. Jordan, the Sunohio consultant who developed the system.

It also would save all of the decontaminated oil that would be destroyed at considerable cost in an incineration process, he said. "It won't be costly in terms of benefit received," he promised. "Compared to other processes, it'll be cheap."