A senior scientist at the Environmental Protection Agency has charged that top EPA officials disregarded extensive evidence that a chemical could cause cancer when they approved using the pesticide to fumigate California fruit bound for Japan.

The pesticide, ethylene dibromide (EDB), is tentatively scheduled to be banned by July, 1983, for use on all agricultural products but was nonetheless approved for use against the Mediterranean fruit fly larvae after Japan threatened not to import California fruit.

Dr. M. Adrian Gross, chief scientist of the EPA's hazards evaluation division, called EDB "probably the most potent and toxic carcinogenic substance used as a pesticide today." He said the decision to minimize test data showing that EDB caused cancer in laboratory animals "could mislead the public about the dangers involved."

Gross, 58, a pathologist and career civil servant, contacted The Washington Post after learning that a story on EDB was being prepared.

Dr. John Todhunter, who has been nominated but not confirmed for the position of assistant administrator for pesticides and toxic substances, recommended approval of the pesticide's use to Anne M. Gorsuch, EPA administrator. Todhunter said he is aware of Gross' criticism, but classified the scientist as a "complainer."

Gross, Todhunter said, "is free to express his personal opinion; he has a doctoral degree in science and is qualified. In this case he is professionally incorrect."

The dispute between Gross and Todhunter is of a type that occurs frequently behind the scenes at EPA and often involves respected scientists. It also points up a continuing dilemma in research on carcinogens, or cancer-causing agents: no one really knows how much of any substance humans can safely tolerate.

The basis for the debate is an EPA "risk-benefit analysis" called PD Position Document 2/3. It stated that the primary dangers to humans from EDB may be in grain fumigation because of the potential for the substance to get into the food chain.

A ban on EDB for agricultural use, the study concludes, is appropriate because "the public health risks of cancer, heritable genetic damage and reproductive disorders outweigh the economic benefits of these uses." That ban was proposed for July, 1983; comments are being sought on that position and a final decision is scheduled for December.

"In allowing the use of EDB in California, we're not saying it is not dangerous; it is as a chemical. What we are saying, is the danger isn't unreasonable," Todhunter said. He said he could not project whether the final position document, set to be released at the end of the year, would continue to recommend the EDB ban.

Todhunter, 31, said his interpretation of a risk-benefit analysis on the pesticide issued by the EPA last December shows that only if people are exposed to repeated contact with EDB could they contract cancer. Todhunter, who holds a doctoral degree in biochemistry from the University of California, reasoned that since the approved use in California would be for only one year, the risks would be minimal.

Liquid EDB is sprayed on harvested fruit as a fumigant in a gas chamber-like device to prevent the spread of the Medfly larvae.

Gross said that "Todhunter is trying to say the risk is one in a million that someone will contract cancer, whereas I find the data to show that the risk is one in a thousand and possibly 50 to 70 per thousand." Gross said the chemical is "much more dangerous than Todhunter believes because it can find its way into finished food products such as breads as easily as it can be consumed" in fruit. EDB was found in virtually all samples of grain taken during nationwide testing, the risk-benefit studied found.

"Accepted scientific studies in the position document clearly show that 80 to 90 percent of the test animals contracted cancer after low-level exposures to EDB, and after a very short time," Gross said.

EDB is most commonly used as an antiknock additive in gasoline. It is also used to control pests in soil before planting, in grain storage chambers, in logs set for market and to control termites in homes.

The chemical has been used for more than 10 years as an after-harvest pesticide on fruit grown in Florida, Texas and Hawaii. No California fruit treated with EDB is supposed to be sold in the United States this year, but some Florida fruit consumed in the Southwest has been treated with EDB. Annually, more than 340 million pounds of EDB are produced by Dow Chemical Corp., Ethyl Corp., Great Lakes Chemical and PPG Corp.

If EDB were to be banned, the alternative method of treatment would be gamma ray irradiation, a method used in some European countries. That process would have to be approved by the Food and Drug Administration before being used in the United States.

EDB is the second chemical to be used against the Medfly that has sparked a controversy about safety. This summer, California Gov. Edmund G. (Jerry) Brown Jr. cautioned against spraying malathion from low-flying aircraft but relented under federal pressures.

Besides Gross, three other pesticide division officials have expressed reservations about Todhunter's decision to allow the use of EDB in California, but none have been willing to speak out publicly. One staffer, who worked on the position document, said he would not eat fruit treated in accordance with Todhunter's "minimum expectations for residue."

Joseph D. Panetta, a program manager who worked on the position document, has maintained that the report is valid and shows that EDB is a toxic, dangerous chemical.

Japanese officials in California recently have indicated they were not concerned about the dangers of EDB and were happy with both the malathion and EDB progam. The Japanese government continues to impose strict standards on imports of California fruit as a result of the Medfly outbreak.