A rare form of cancer contracted by seven herbicide manufacturing workers "strongly suggests" that dioxin can cause cancer in humans, according to the chief of surveillance for the National Institute for Occupational Safety and Health (NIOSH). If diagnoses by the victims' doctors are confirmed by the Armed Forces Institute of Pathology, the cases will become evidence that the controversial chemical--highly carcinogenic in animals--can cause cancer in humans.

The seven rare cancers, called soft tissue sarcomas because they attack muscle, fat, nerves or connective fibers, were discovered in studies of between 3,000 and 4,000 workers exposed to dioxin. Soft tissue sarcomas normally appears once in 50,000 persons in the general population suggesting that the incidence in the chemical workers may be related to dioxin exposure.

Dioxin, an unwanted contaminate of the manufacture of herbicides and related chemicals, is one of the substances most toxic to animals.

Dioxian oil compound that was sprayed on roads to keep down dust in dozens of Missouri communities, and has been recently discovered in other sites across the country. The Environmental Protection Agency evacuated and bought the entire town of Times Beach, Mo., after dioxin washed through the community during a flood this spring.

Chemical companies' officials, however, have said that there is no proof that dioxin causes anything more in human than a sometimes severe skin disease, called chloracne.

Dr. Philip Landrigan, chief of surveillance, evaluation and field studies for NIOSH, cautioned that samples of the suspected cancer being studied at the Armed Forces lab for final confirmation of diagnoses.

"To be absolutely certain there's a cause-and-effect relationship" between dioxin exposure and cancer, "we want this confirmation" and "we need to investigate more cases," Landrigan said.

"But to me," he added, "the evidence is very strongly suggestive that occupational exposure to dioxin can cause cancer."

Although workers for other companies were included in the the seven cancers were found in workers at the Dow Chemical Co. and the Monsanto Co.

Dow and Monsanto doctors have said the findings on dioxin's role as a long-time hazard are inconclusive. "If you force me to say is it or is it not, I'd have to say I want to see some further research," said Dr. Ralph Cook, director of epidemiology for Dow.

Dr. William Gaffey, who holds the same position at Monsanto said, "I don't think we can say until we have an opportunity for a longer look."

Four of the workers, all now dead, were involved in the man of 2,4,5-T and related herbicides or their chemical components, compounds commonly contaminated by dioxin, Landrigan said.

The other thr said, may have been exposed because they worked in plants where such products were made. One of the three is still alive.

Officials at the Environmental Protection Agency's Health Effects Research Laboratory in Cincinnati are examining independently a set of EPA reports saying that th other evidence show that dioxin "probably" can cause human cancers, an EPA spokesman said.

The Dow and Monsanto cases were disclosed in medical journals two years agoir significance was debated at the time, because of varying results in different studies.

It is unclear, too, whether these studies show major hazards from lower-level exposures, the kind that might be more applicable to the general population. Most of the chemical workers were either exposed for several years, had massive shorter-term exposures or both.

The Dow and Monsanto experiences "don't tell us whether or not" low-level exposure is harmful but do dictate caution, Landrigan said.

Chemicay officials say that industrial exposure to dioxin has caused many cases of chloracne, a skin disorder that can sometimes escalate into serious liver, blood or nerve problems. But both industry and government officials have repeatedly said that there is no proof that dioxin has caused even worse effects, like cancer.

Swedish scientists first reported five years ago that lumberjacks and other laborers exposed to dioxin suffered five to six times the expected number of soft tissue sarcomas.

Dow and Monsanto independently studied four groups of their workers at plants in Midland, Mich., and Nitro, W.Va. None of these studies seemed to show a statistically abnormal number of the rare tumors.

But NIOSH epidemiologists added up these populations and added possible cases reported by other doctors. This produced the seven cases under investigation, two among Dow workers, five among Monsanto's.

Information on the length and intensity of the workers' exposures is incomplete. Dow's Cook said that one of the Dow workers was first exposed to suspect substances in 1964 and died in 1975. The other was first exposed in 1951 and died this year. Both were part of a group inadvertently over-exposed for three to nine months in 1963-64 when a manufacturing change released unexpectedly large quantities of chemicals.

At least two of the seven victims being studied by NIOSH were heavy smokers, Cook said. Scientists know cancer may sometimes be caused by smoking in combination with a chemical exposure.

Gaffey said three of the Monsanto victims worked at the Nitro plant where a 1949 explosion may have spread chemicals. He said two of the three might have been involved in the cleanup after the accident. The third, a clerk, had "minimal opportunity" for exposure, he said.

The final Monsanto cases involved a father and son who worked at an East St. Louis, Ill., plant. Gaffey said that the father was a maintenance worker exposed to unknown amounts of dioxin and that the son, a clerk, was diagnosed as having a soft tissue sarcoma two years after he went to work. The son is dead; the father is alive.