An environmental toxicologist says that he warned federal and Missouri state officials two years ago about potentially hazardous dioxin contamination in Missouri and that his concerns still have not been addressed.

Dr. James W. Singmaster, a toxicologist at the University of Puerto Rico, said in an interview yesterday that he wrote Missouri officials in June, 1981, warning them that thousands of gallons of waste from a chemical plant in Verona, Mo., had never been accounted for.

The plant, now closed, was the source of much of the dioxin-contaminated chemical waste that was mixed with oil in the early 1970s and sprayed over hundreds of miles of dirt roads in eastern Missouri.

In August, 1981, Singmaster said, he expressed the same concerns to Environmental Protection Agency officials, including then-Administrator Anne M. Burford.

"I got back answers which indicated they didn't understand the problem at all," he said.

The "problem," as Singmaster sees it, is that while health officials are busily testing soil and water samples for the presence of dioxin, a potentially deadly byproduct of some chemical production processes, no one has satisfactorily accounted for the waste products from chemical companies that produced the contaminated chemicals.

According to Singmaster, some of those wastes contain dioxin stripped from chemicals in "cleanup" operations and may contain dioxin at far higher levels than the contaminated chemicals themselves.

"There are at least 250,000 gallons of waste that need to be accounted for," he said. "It may be as high as 1 million gallons." Singmaster said that his estimates are based on the output at the Verona plant, which produced 20,000 gallons of waste a year.

"They'll find it eventually," he said, "because they'll find high levels of dioxin in some dump somewhere--levels of 20 or 30 parts per million."

The federal government's unprecedented buy out of Times Beach, Mo., came after tests showed dioxin contamination 100 times less concentrated than that, at 300 parts per billion. The federal Centers for Disease Control considers a level of 1 part per billion to be cause for concern.

Singmaster, who initially worked from a 1980 EPA document that listed more than 100 plants where chemicals suspected of dioxin contamination were made, blended or shipped, said that he wrote to state officials in New Jersey in April, after talking to a chemist who had formerly worked at the Diamond Alkali Corp. plant in downtown Newark.

That plant site was ordered quarantined Thursday after tests showed dioxin levels ranging up to 500 parts per billion.

Singmaster said that the chemist, whom he declined to identify, told him about two explosions at the plant and widespread health problems among its employes.

"I suggested to New Jersey that they should look to find information about the explosion. A Seveso-like effect could have occurred," Singmaster said, referring to a widely publicized industrial accident at a drug manufacturing plant in Seveso, Italy, in the mid-1970s that resulted in a rain of dioxin-contaminated ash.

Singmaster said he received no response from New Jersey Gov. Thomas Kean and Newark Mayor Kenneth Gibson.

New Jersey officials could not be reached for comment yesterday, but a spokesman for the regional EPA office in New York had said earlier that no one in the office had seen or heard of Singmaster's letter.

By April, however, New Jersey had established a dioxin task force, prodded into action by Missouri's mounting dioxin problems. The Diamond Alkali site was the task force's first target.

Singmaster's letter was not the first warning the state received about the site, however. The Associated Press reported last week that a former owner of the site told state officials in July, 1981, that the area was heavily contaminated with dioxin.

The former owner, G. William Mitchell, also told the AP of his concerns, which reported that it was unable in 1981 to get any state or federal officials to confirm that a problem existed in Newark.

Singmaster said yesterday that his intent is not to raise additional public concern about dioxin but to refocus attention on what he considers "the biggest problem, which hasn't been addressed, yet. Where are all the wastes from these plants?"

He said that his dioxin research was undertaken in an attempt to disprove the theory that Vietnam veterans have health problems as a result of exposure to Agent Orange, a defoliant that contained dioxin as an impurity.

Dioxin, he said, was present as a contaminant in hundreds of products containing trichlorophenol (TCP), a disinfectant chemical in wide use in the United States for more than three decades. Among the chemicals made with TCP was hexachlorophene, which at one time was found in everything from acne treatments to toothpaste.

"Traces in those products, if used daily, would greatly exceed any exposure Vietnam vets had," Singmaster said.

Hexachlorophene has since been banned for all but restricted use as a hospital disinfectant, in highly diluted and purified form.

At the highly concentrated levels likely to be found in chemical wastes, however, dioxin is a significant concern, Singmaster said. "These wastes are still loaded," he said. "If they're buried and they leak into the water table, there could be very serious contamination."