Several Environmental Protection Agency officials, directly contradicting the testimony of acting EPA Administrator John W. Hernandez Jr., testified yesterday that they were pressured to change a report on dioxin contamination and were told that the orders came from Hernandez.

Valdus V. Adamkus, the EPA's Chicago regional administrator, said Hernandez telephoned him three times in the summer of 1981 and told him to expect a call from Dow Chemical Co., which sought to make changes in an EPA report that identified Dow as the major source of dioxin contamination in two Michigan rivers.

Adamkus told the House Energy and Commerce subcommittee on oversight and investigations that Hernandez "angrily denounced the report and called the work of our regional people trash." Adamkus testified:

"In very strong language, he discredited the qualifications of our regional people working on the study and said I should expect a call from the company officials and I should talk to them. It was a strict instruction."

Two of Adamkus' assistants also said they were told that John A. Todhunter, EPA assistant administrator for toxic substances and pesticides, insisted that a study linking dioxin to miscarriages be deleted along with other references in the report that Dow considered unfavorable.

In a statement late yesterday, Hernandez said: "It is unfortunate that Mr. Adamkus misconstrued my concerns for the study's validity as a tacit order to make the changes." He said he was disturbed by "the apparent conflicts in my testimony and that of Mr. Adamkus," but added that "it's been 18 months since the conversation in question."

Todhunter also strongly denied that he ordered any changes or deletions in the report on the toxic herbicide byproduct, or that his name was used in requesting the changes, according to an EPA spokesman. He said Todhunter could not account for the contradictory account in yesterday's testimony.

At the urging of both Dow executives and EPA officials in Washington, the witnesses said, they deleted statements linking dioxin to cancer and birth defects, as well as their conclusion that Dow was "the major source, if not the only source" of dioxin contamination near the company's plant in Midland, Mich.

Dr. J. Milton Clark, a scientist in EPA's Chicago office, said he repeatedly was urged to soften the report's language by EPA scientists in Washington, one of whom told him "that some changes in the report had been dictated by Dr. Hernandez."

Asked about Hernandez' statement Wednesday to another House subcommittee that he did not order any changes in the dioxin report, Clark said: "To the best of my knowledge, that would not be an accurate remark."

Clark said that, during a conference call, "Dow officials went page by page with us through the document, starting with the title."

Adamkus said he went along with the changes because "we determined the Dow comments carried a very heavy load with our headquarters, and if we want to get the blessing of headquarters to release the report, we definitely have to do something about this. They actually repeated the same request to us from Washington that we heard from the Dow people.

"It is unethical, unusual, unprofessional to get an internal document reviewed by an outside company," Adamkus said. Under questioning by Chairman John D. Dingell (D-Mich.), Karl Bremer, another EPA official in Chicago, said an aide to Todhunter told him that her boss wanted to delete references to a 1979 EPA study linking dioxin to miscarriages and to Agent Orange, a herbicide containing dioxin.

"She told me her job was on the line during that discussion," he said. "She told me Dr. John Todhunter had instructed her to have those lines removed....These were his orders to her."

Hernandez has said he shared the report with Dow because a draft version already had been leaked to a Toronto newspaper and because career EPA scientists had questioned the findings--including a warning not to eat dioxin-contaminated fish in Michigan--before he joined the agency.

Clark's notes showed that one EPA scientist in Washington told him the study should not be released because it "implicates industry" and "it will inflame the public." Dow officials have said that their comments were part of a routine peer review and that, despite various animal studies, there is no evidence that dioxin poses a threat to human health.

"The message of this administration is that the public does not deserve the truth about the health consequences of exposure to toxic substances," said Rep. Edward J. Markey (D-Mass.).