At an Aug. 20, 1963, press conference President Kennedy said in answer to a question that there was evidence of a possible radioiodine hazard to residents near the Nevada nuclear test site. It was "a matter of concern" said Kennedy and requires further study," However, he added "as of now . . . we do not believe the health of the children involved has been adversely affected." President Kennedy's position, therefore, was not quite as firm that the test had had no health effect as reported yesterday in The Washington Post.

A top federal health official said today that government agencies-including those responsible for public health-ignored and covered up growing evidence in the '50s and '60s that atomic bomb tests harmed people downwind who were exposed to the bombs' radioactive fallout.

The acknowledgement by Peter F. Libassi, general counsel of the Department of Health, Eduction and Welfare, was joined by Sen. Edward M. Kennedy (D-Mass), who denounced the "misrepresentation and distortion . . . the misleading information and the studies that were submerged by the Atomic Energy Commission."

Together, those allegations represent perhaps the highest-level attacks ever made in a quarter-century of controversy about the health effects of nuclear testing in Nevada. They came during a day of joint congressional hearings on fallout health effects conducted by Kennedy's subcommittee on health and scientific research and the House subcommittee on oversight and investigations, headed by Rep. Bob Eckhardt (D-Tex.).

The hearings were among the first ever held on the subject by congressional committees not also responsible for developing nuclear weapons and nuclear power. And perhaps not coincidentally, they contrasted sharply with those held in 1959 and 1963 by the Joint Committee on Atomic Energy.

Today, there was a mood reflecting a virtual assumption that a decade of tests from 1951 to 1962 had indeed caused leukemia, cancer and livestock losses in areas regularly dusted by the fallout from nearly 100 nuclear detonations at the Nevada Test Site.

In many cases, questions and statements by congressmen and senators, as well as responses by witnesses, reflected a growing belief that the only issues left to be resolved are how to prevent future disasters, how to compensate victims or their families and how to lay bare fully the actions of bomb-testing and public health officials.

In past years, residents of the fallout zone who had complained of ill health caused by fallout had been met by their elected officials with statements that their fears were "Communist-inspired scare stories."

But so great a change has occurred that Kennedy's allegations effectively refuted statements by his own brother, the late President Kennedy, in 1963, that nuclear testing had not increased thyroid abnormalities and thyroid cancer in Utah.

Today's hearing was played out against a backdrop of recurring references to the failure of a nuclear power plant at Three Mile Island in Harrisburg, Pa. Repeatedly, witnesses were questioned by by Sen. Richard S. Schweiker (R-Pa.) about any similarities between Three Mile Island and nuclear testing, including "the ability of government officials" to candidly address radiation risks.

Today's 5 1/2 hours of testimony, broadcast live by a local television station and covered heavily by local and national news media, included appearances by sheepmen and scientists, the governor of Utah and the survivors of leukemia victims.

There was the narrative presentation of Gov. Scot M. Matheson alleging a widespread cover-up of fallout effects and the heart-tugging words of a leukemia victim's daughter that if residents had only been warned of potential dangers, they could have protected themselves.

While Kennedy focused on the seeds of distrust in government that federal officials sowed in the '50s and '60s among fallout area residents, Eckhardt concentrated on atomic power as "permanent pollution" and the methods by which victims of fallout can be compensated for their losses.

The sheepmen and survivors expressed both their financial loss as well as the loss of their faith in the government in which so many of them believed.

Among the highlights of today's testimony were:

Kennedy's and Libassi's disclosure of a 1954 AEC news release exonerating fallout as the cause of the bizarre deaths of hundreds of sheep in Utah. The release says that the U.S. Public Health Service concurred with that finding, when, in fact the service had not.

Testimony by Dr. Joseph L. Lyon, a state epidemiologist who concluded last February that children growing up in the fallout areas of Utah in the 1950s suffered 2 1/2 times as much leukemia as children living there before and after testing.

Lyons said today that additional study has strengthened the case for fallout as a cause of the leukemia and that fallout is the "leading contender, with whatever is in second place way back." Lyon said that all but one of the 32 children from the fallout zone who died of leukemia had lived there all their lives.

Claims by Dr. Harold Knapp, a former AEC official, who was virtually forced to resign in 1963 after concluding that residents received far more exposure to fallout than the the AEC and fallout recipients.

His work was discredited in the agency by another official who said it would be "harmful" to the "good relations" built up over the years between The AEC acknowledged.

Sheepmen told of losing their stock to radiation and being insulted by AEC investigators who tried to make them think that they themselves were responsible for their sheep losses.

But by far, the most significant testimony of the hearings to date which continue in Las Vegas on Monday, was that of Libassi, the top lawyer in HEW and chairman of a Carter administration task force on the health effects of radiation.

Under questioning from Kennedy, Libassi acknowledged the government's past "reluctance or unwillingness to address the questions" of diseases related to fallout, or "to pursue the reasons and to disclose the results . . . to the American people."

He added. "There was a general attitude that the American people could not be trusted to deal with the questions."

Asked by Rep. Gunn McKay (D-Utah) if the unwillingness to disclose problems extended to HEW and its Public Health Service, Libassi answered. "I don't believe any agency is free of criticism." Ironically, the Congress in 1958 took from the AEC and gave to the Public Health Service the responsibility for monitoring the health effects of fallout.