The American Medical Association accused the news media yesterday of conducting a "witch hunt" against the toxic chemical dioxin, and decided to mount a public relations campaign to counter the "hysteria."

By voice vote, its 351-member House of Delegates decided in Chicago that the AMA will adopt "an active public information campaign . . . to prevent irrational reaction and unjustified public fright and to prevent the dissemination of possibly erroneous information" about the health hazards of dioxin.

Dr. George Bohigian, a member of the AMA council on scientific affairs and sponsor of the resolution, said that no serious medical effects on humans have been found to have resulted from the dioxin accidents and spills studied over the past two decades.

Bohigian said that medical reports, including a 1981 AMA survey, have found only two short-term effects of dioxin on humans. One is a skin condition called chloracne, which is similar to severe acne. The other is apparently temporary nerve damage that causes numbness and similar effects.

Bohigian is an opthalmologist at Washington University in St. Louis, in a state with some of the nation's worst dioxin contamination.

Meanwhile, an editorial in the current issue of Science magazine, published by the American Association for the Advancement of Science, said that while dioxin is highly toxic when swallowed, "it does not pose much of a hazard" in soil.

The editorial called for controls on "unwanted industrial production" of dioxin and on its formation "in the incineration of municipal waste." It added that "natural degradation" will clean up the problem eventually.

Dioxin is the shorthand name for a common contaminant of some manufacturing processes. It is found chiefly in plant-killing chemicals, including Agent Orange, which was used by the U.S. military in Vietnam.

Not long ago it was found in waste oil sprayed to control dust on Missouri roads. As a result, residents of Times Beach were forced to leave their hamlet permanently.

It also has been found elsewhere, including at three sites in New Jersey.

Irving Selikoff, a specialist in environmentally caused cancer at the Mt. Sinai Hospital Medical Center in New York, agreed that "we should not be saying things we don't know about."

"But the situation is difficult because we have here a substance that causes cancer in animals . . . and birth defects in animals," he said. "In the short-term accidents it is true that we do not see . . . disease, but it is also true that dioxin accumulates in the body. And we don't know its long-term effects."

Researchers for the National Institute for Occupational Safety and Health have reported that there is some evidence from Swedish studies and three American studies that workers in industries where 2,4,5-T and dioxin are present get more soft-tissue cancers than other workers.

The AMA resolution passed yesterday said, "The news media have made dioxin the focus of a witch hunt by disseminating rumors, hearsay and unconfirmed, unscientific reports . . . attributed to scientists whose quotes should have been, 'I don't know.'

"The lives and well being of many inhabitants of the regions contaminated have been unnecessarily and ignorantly damaged by this type of malreporting."

Bohigian said that when a chemical plant exploded in Seveso, Italy, in 1976, more than 37,000 people were exposed to dioxin but that no long-term ill effects have been reported.

He acknowledged that such ill effects as cancer may eventually show up in those exposed to dioxin. "But I think cigarettes probably do a lot more damage than dioxin ever will," he said.

"The problem goes beyond Missouri," he said. "The larger issue is what do we do with any area that is contaminated . . . . It's dioxin now, but next time it's going to be something else."

In voting yesterday, the AMA also went on record against federal "Baby Doe" laws to force doctors to treat severely handicapped newborns.