The Environmental Protection Agency announced today it would not approve a North Carolina proposal to treat soil contaminated with toxic polychlorinated biphenyls (PCBs) where it rests along 211 miles of state roads.

In a letter to Gov. James B. Hunt Jr., Administrator Douglas Costle said he made the decision because he knows of no alternatives to putting the material in EPA-approved chemical waste landfills or incinerating it.

" . . . This is a very difficult decision to make," Costle wrote. "Our concern was not that there would be an imminent threat to humans if PCBs were mixed and contained in place as proposed by the state, but rather that this method could result in an unknown and uncontrollable human exposure."

However, Hunt's press secretary, Gary Pearce, said the EPA decision is not binding on the state. He said the federal Toxic Substance Control Act of 1976 does not give the EPA authority to prevent the state from leaving the PCBs on the roads. The EPA also said that is the case.

Pearce said Hunt will decide in the next 10 days whether to treat the PCBs along the roads or scrape up the estimated 50,000 tons of contaminated soil and hault it to an approved chemical waste landfill.

Thousands of gallons of oil laced with PCBs were dumped along state roads in 15 counties last summer, creating the disposal problem. PCBs, used primarily in electrical insulators, cause skin and internal disorders in humans and have been linked to cancer and birth defects in laboratory animals. The chemical does not break down easily in the environment and can be ingested, inhaled or absorbed by humans.

In Atlanta, EPA Regional Administrator John White today approved a separate North Carolina proposal to dump the PCB-contaminated soil in a site in rural Warren County, about 50 miles north of Raleigh near the Virginia line. Residents have angrily opposed a chemical dump there.

White agreed to allow three waivers of EPA requirements, including one that would place the PCB soil 10 feet from the seasonal high ground water table. EPA requirements call for a 50 foot separation. White said the EPA must still approve final plans and specifications before the dumps could be built.

Hunt petitioned Costle in February to approve the state's plan to treat the roadside PCBs in place with activated charcoal, a process he said would bind, and thus neutralize, the chemical.

In another development, three Jamestown, N.Y., men pleaded guilty today to reduced state charges stemming from the PCB dumping. Robert Burns, and his sons Randy and Timothy, pleaded guilty in Halifax County Superior Court to two counts each of felonious damage to public property.

In the agreement, the Burnses agreed to testify against Robert Earl (Buck) Ward Jr., and his son Robert Earl (Bob) Ward III, and the Ward Transformer Co., all of Raleigh. The Wards and the company are charged with conspiracy and being accessories to the PCB dumping.