Michael Gross, a University of Nebraska chemist under federal contract to search for highly toxic dioxin in fat samples from Vietnam veterans who may have been exposed to the defoliant Agent Orange, found the samples so heavily contaminated with the poisons PCB and DDT that the traces of dioxin were at first obscured.

In Chicago, a toxicologist testing hair samples from 41 Vietnam veterans was puzzled when he found abnormally high traces of poisonous metals in the samples. John Bederka of the University of Illinois Medical Center discovered the results were such a departure from the norm that he is repeating the tests, using hair samples from nonveterans as a control.

In Kalkaska, Mich., Dr. Guy Arnold, a 37-year-old veterinarian who is partly paralzyed and going blind, tells of working as a scout-dog handler in Vietnam and swabbing dogs with chlordane, a powerful pesticide, to rid them of ticks and fleas. An Army study found that dogs in 20 out of 22 dog-scout platoons in Vietnam died because of internal hemorrhaging. Today, Arnold suspects that his exposure to the pesticide was responsible for his ills.

For countless Vietnam veterans, the words "Agent Orange" have become a symbol for the delayed price of war. The code name for the jungle herbicide conjures up apocalyptic visions of chronic illness and tormented lives. Agent Orange has given bitter focus to the anguish of a veteran's previously unexplainable fatal tumor or his deformed child.

But the explanation may turn out to be too simple. In the midst of the controversy over Agent Orange, evidence is emerging that the veterans' ills may be related to exposure in South Vietnam to a far more complex "toxicological cocktail," as one scientist put it with grim whimsy.

Scientific studies point to the toxic potential of a variety of chemical and biological substances to which American servicemen were exposed. Although the toxic potential for some of these substances is well known, no one has studied their combined effect or what scientists call "synergism" -- the ability of two or more substances together to produce effects greater than they would individually.

"There has been undue preoccupation with Agent Orange," says Dr. Samuel Epstein, author of "The Politics of Cancer," a professor of occupational and environmental medicine at the University of Illinois' School of Public Health. "To base all conclusions about toxicity in Vietnam veterans on Agent Orange is simplistic."

Epstein, a critic of the government's cancer research, has refused to join the veterans in their legal battle over Agent Orange because he thinks that the focus on dioxin alone is misguided. "You have a dozen toxic agents in Vietnam. Some, like chlordane, are unequivocally carcinogenic, others like dapsone, an experimental antimalarial drug, are very suspect. What you had in Vietnam was a toxicological cocktail. It's impossible, on theoretical grounds, to make predictions on exactly what the eventual effects of all the chemicals could be. From an epidemiologist's point of view, it would be a nightmare."

In some instances, military authorities used chemicals they were convinced would have no ill effect on troops, though later studies caused them to discontinue their use, as in the case of Agent Orange. In other instances, the dangers were taken into account but the risk-benefit trade-offs were accepted as a price to pay in waging war.

The use of dapsone, for example, generated serious internal debate with the U.S. military command in Vietnam when it was first adopted in 1966 and at least one top surgeon serving with the Marine Corps opposed its use.

Dapsone, used successfully for decades to control leprosy, was given daily in the form of white tablets to most combat troops beginning in 1966 to ward off a type of malaria thought to be resistant to the standard orange chloroquine tablets. The use of dapsone was discontinued after 16 soliders became ill with agranulocytosis, a kind of bone-marrow disorder resulting in abnormal white-blood-cell production, and eight of them died of the disorder, which was linked to dapsone use.

In the mid- and late-1970s, studies here and abroad showed the chemical to be a potential carcinogen in male laboratory rats, though it did not affect female rats or mice.

Veterans who say they were exposed to Agent Orange had complained of having suffered skin rashes, changes in skin pigmentation, sudden loss of appetite, insomnia, blurred vision, dizziness and ringing in the ears in Vietnam. The same symptoms were reported among the effects of dapsone in a scientific paper by Dr. Walter R. Graham of the University of Pennsylvania's School of Medicine.

But toxic dangers in Vietnam did not only come from chemical agents. The troops' presence in Vietnam exposed them to toxic dangers in the tropical enviroment. Eating native rice contaminated with mold may have exposed soldiers to one of the few naturally occurring carcinogens known, aflatoxin.

"Aflatoxin occurs as a fungus on native rice in Vietnam, and it was a problem on all cereal grains in Vietnam," said U.S. Air Force Maj. Alvin Young, a plant physiologist with the epidemiology division of the U.S. Air Force School of Aerospace Medicine at Brooks Air Force Base in San Antonio. "In combat, troops ate what they could find. And sometimes they ate moldy native rice.

"Look, war is hell, okay? But we tried to use techniques to save our own lives. Who knows how many troops were saved from malaria because we used dapsone and sprayed 400,000 gallons of malathion [an insecticide] from 1967 on? We used what was available at our levels of technology at that time."

In all, a dozen or more potentially toxic agents may need to be studied and related to Vietnam veterans' individual exposure.

The Veterans Administration, which will ultimately have to handle the problem, is not ready yet to deal with the question of synergism.

"We've talked about it, taken account of it," said Dr. Barclay Shepard, special assistant for Agent Orange to the VA's chief medical director. "But we just can't study that question in depth here. We have to limit ourselves to what causes the most public concern, and that's Agent Orange. We have our hands full with that."

Some scientists are skeptical the VA has the expertise to deal with the question of interaction of toxic substances. "They are incapable of doing that kind of work," said Bederka, who has done tests on hair samples from veterans for arsenic related to Agent Blue, a herbicide used to kill rice crops. "We are talking about a vast array of chemicals that is so pervasive that it would be comparable to what people are finding at Love Canal.

"In fact, some of the Vietnam veterans are showing the same problems as the Love Canal people. To me, it's an impossibility to separate the effects of dioxin from all the rest. It would not be at all surprising to find additive or even synergistic effects."