Federal investigators tracking PCB from a leaky Montana electrical transformer have traced PCB-TAINTED animal feed and agricultural products into 19 states, Canada and Japan in what officials say is the most widespread chemical contamination incident they have ever encountered.

PCB is polychlorinated biphenyl.

Federal and state officials involved in the massive search said their laboratories are so jammed with samples waiting to be tested for PCB that they have been unable to tell farmers with suspect livestock, feed and eggs what to do.

"We've had hundreds of calls from farmers who think they may have a problem," said W. Gordon McOrmber, director of Montana's agriculture department. "We are telling them don't dispose of it, don't eat it and don't kill it, just bear with us."

In addition to tracking raw foods suspected of PCB contamination, investigators for the U.S. Food and Drug Administration have started tests on processed foods in six states to determine whether they also contain the chemical.

PCB is a suspected carcinogen that has caused skin disease and other health problems. Production of the chemical compound was banned in 1976 by the government, but PCB is still widely found in electrical transformers and industrial machinery, where it is used as a high-temperature coolant and lubricant.

The Environmental Protection Agency estimated this year that there are still about 45 million electrical transformers in use that are filled with oil containing PCB.

Investigators have identified the source of the recent food contamination as a damaged transformer in a storage shed owned by the Pierce Packing Co. of Billings, Mont. Some 200 gallons of the PCB leaked from the transformer sometime around June 20 of this year, investigators said.

According to the FDA, PCB became mixed with bone and meat meal at the Billings plant. Since June 20, the plant has shipped about 2 million pounds of the meal to feed prepared primarily for hogs and poultry.

Most of the feed manufacturers who received the tainted meat and bone meal are in Montana, federal officials said. But during the time of the leakage until the PCB investigation began, the chemical has spread widely, the officials said.

In interviews yesterday federal officials said the PCB contamination incident was a virtual case study in the multiplication effect that can occur once even a small amount of contaminant gets into a food chain.

Federal investigators have tracked the PCB to mink farms in Manitoba, chicken soup makers in Minnesota and a mayonnaise distributor in the state of Washington. Chickens contaminated with the chemical went into frozen food lockers in Ennnsylvania, New Jersey and Kansas, while eggs with PCH in them went to Utah and Idaho, investigators said. TThe U.S. Department of Agriculture and the FDA are investigating 40 to 50 western slaughterhouses which apparently received the contaminated animal feed and one shipment of nearly 10 million pounds of contaminated chicken grease that ended up scattered between Japan, Canada, Washington and Oregon.

The FDA said it notified Canadian officials last Friday about the PCB contaminated products and told the Japanese embassy this week that the PCB-TAINED chicken grease was on a freighter bound from Seattle to the Misubishi Crop. of Tokyo.

Officals said Montana has been the hardest hit by the chemical contamination. Supermarkets in the state have begun advertising that their eggs and poultry come from outside the state. Investigators said the use of feed with PCB in it has been widespread. One check showed that 700 farmers in a single community bought feed suspected of contamination with the chemical, they said.

"The whole thing is terribly complicated," said Anthony Celeste, the FDA official heading the agency's search for the chemical. Celeste said FDA has almost 100 people assigned to the search.

Federal officials are expected to spell out the full extent of the contamination they have uncovered up to now in hearings scheduled to begin today before the House Commerce subcommittee on oversight and investigations.

Rep. Bob Eckhardt (D-Tex.), chairman of the committee, said the panel will also be looking into a six-week lag that he said occurred before agriculture department officials notified the FDA about the chemical contamination.

Carol Tucker Foreman, assistant secretary of agriculture, said this week that her department's investigators had been "slovenly and unacceptable" in their handling of the PCB incident.