Of all the horrors of war, few are more chilling than biochemical weapons. They were outlawed by the 1925 international Geneva Protocol, and both the U.S. and the Soviet Union among other nations renounced their use in a 1972 agreement. Yet last month Secretary of State Alexander Haig ignited a Cold War furor by expressing alarm that the Soviet Union may have unleashed "lethal chemical weapons" in Southeast Asia and Afghanistan. The State Department later confirmed that an independent investigation by American journalist Sterling Seagrave, 44, had been "instrumental" in bringing the problem of chemical warfare in Southeast Asia to the attention of the government. In his new book Yellow Rain (Evans, $11.95) Seagrave tells how his four-year quest through Laos, Yemen and Afghanistan led him to the conclusion that "large-scale poison warfare was going on for the first time since World War I." Seagrave, son of Dr. Gordon S. Seagrave—the "Burma surgeon" of World War II fame—was born in Ohio and worked as a Washington Post assistant foreign news editor for two years and as editor of an English-language magazine in Bangkok for six years. "I grew up as a mountain boy among people very like those under attack in Laos," he remembers, "and when they first told me of their plight, I couldn't turn my back on them." Seagrave discussed his charges with John Stickney of PEOPLE.

What poison are the Soviets using?

The main chemical agent I found was tricothecene toxin, known as T-2, which occurs naturally in grain molds. Refined from fungus and souped up in the lab, it is as virulent as the most potent synthetic poisons. T-2 can be suspended in the air in a dust cloud. You can breathe it, swallow it or even just get it on your bare skin. You can survive small doses with considerable pain and injury, but all three ways in heavy concentration will kill you in minutes.

How does T-2 kill?

It is grotesque. Firsthand accounts describe how it causes your blood vessels, arteries and capillaries to contract and your tissues to rupture so that the blood inside your body explodes, and you become a walking hemorrhage drowning in your own blood. Meanwhile you're burning with what they called St. Anthony's Fire in the Middle Ages. You're also having spasms and convulsions resembling St. Vitus' Dance. Since there's no place for the blood to go, and the poison brings on a violent retching and purging, you're vomiting pints of blood and bleeding out of every orifice in the body. It happened that way in the Middle Ages and, by God, it's happening the same way now in Laos.

Would a gas mask protect you?

The most sophisticated available mask can handle nerve gas, but to my knowledge a biotoxin like T-2 has never been tested. The T-2 molecule is so small that it might penetrate the mask filter anyway. One component of the poison makes you want to take off your mask and vomit.

Why would T-2 appeal to the Soviets?

One reason is that, as an organic mold common in bread, it's been killing people in Russia for hundreds of years. It isn't a novelty to them. They have been producing T-2 since the late 1940s. Its virtue is that, as a natural poison, it dissipates in about 24 hours and is harder to detect than a synthetic. T-2 contaminates food and water for short periods. It could be argued that the death symptoms occur in nature. It's easy to see why they've moved into biologicals.

Are biotoxins new to warfare?

Since the Middle Ages enemies have been trying to set plagues upon one another. The problem with germ warfare is that once you let the bugs loose and an epidemic starts, the bugs can come back to bite you. With biotoxins you have the bug juice without the bugs—you can spread poison without fear of contagion.

What do you mean by "yellow rain"?

It's a silicone-based powder, not poisonous in itself, to which the poison is bonded for ready delivery under all sorts of atmospheric conditions. At first bright colors were used, but now it's a dirty yellow or yellow-brown cloud that descends upon the victim. In Afghanistan, China and elsewhere along Russia's non-European borders, the powder often blends right into the landscape—almost as if it had been specifically designed that way.

Are the Soviets the source of the poison weapons?

Intelligence reports indicate that they're making it standard issue for some of their allies, who are most likely experimenting with the poison for them. But in Yemen during the mid-1950s Russian pilots were reportedly seen dropping yellow rain from planes with Egyptian markings. In Indochina Russian officers—including a general—were monitored while supervising chemical depots. Laotian hill people under attack from Vietnamese planes claim to have seen Caucasian observers aboard. They could have been Soviets or Cubans.

What about the Cubans?

For some time the Soviets have been training them in both offensive and defensive chemical warfare. I've seen a copy of an autopsy on a Cuban spy who died suddenly on the island, and it showed his grisly death was almost surely from T-2. Fidel Castro has reportedly boasted that he has the capacity to loose hoof-and-mouth disease on the U.S. Unfortunately, he might not be squeamish about his choice of weapons after all the clumsy CIA attempts to poison him.

Do you have casualty statistics?

They're not easy to come by anywhere, and especially in countries like Afghanistan and Cambodia. In Yemen 15 to 20 villages were gassed in the 1960s, with deaths in each ranging from 40 to 400. In 1979 Laotian hill tribe elders were reckoning the death toll at more than 15,000. By now the Laotian totals alone may run to 30,000.

But can you prove these charges?

The evidence is circumstantial, I admit. But I have talked to hundreds of eyewitnesses of these deaths. In Laos, for example, I relied on my own interviews, along with British, French and American intelligence reports. I also have used testimony before Congress of a U.S. Army medical team that examined survivors. In Cambodia, moreover, the State Department claims to have found the smoking gun. It was a single leaf saturated with poison, but size isn't the issue: The concentration of three toxins on that leaf was 400 times as much as necessary to kill a human being.

How could these deaths go so long undetected?

Word is less likely to get out from remote places, and the reports were usually disputed anyway. Though the death symptoms pointed unmistakably to chemical warfare, poison traces were analyzed and destroyed in futile search for some old-fashioned variety left over from the world wars. Biotoxins like T-2 were so novel—and so bizarre—that they defied the imagination. There are so many good old ways of killing. The Russians have proved that by going back to the Dark Ages and getting one.

Is there a strategic explanation for the resurgence of chemical warfare?

The nuclear standoff has forced us to be innovative. The object now is to outwit the enemy with a weapon for which he isn't prepared. At least you might gain some political or diplomatic leverage. The Soviets are well aware that they have us at a disadvantage because the issue of chemical warfare is so explosive in the U.S. We're still embarrassed about Agent Orange and the other defoliants that we used in Vietnam. But they were used foolishly, not maliciously. Nobody's confused about whether T-2 is there to burn leaves or to kill people.

Why is chemical warfare so psychologically devastating?

Since you can't grab poison gas or dust, they seem to be ethereal, almost supernatural, and for psychological reasons it's all the more frightening because of that. People believe they can duck or dodge a bullet, or maybe even survive a nuclear blast, but gas seems to penetrate every defense. Though the threat of an attack can throw a city into a panic, gas is an especially useful tactic in caves, mountains and jungles, where bullets and other ordnance aren't always effective.

In 1969, partly because of the uproar over Agent Orange, President Nixon banned U.S. biochemical weapon production. Does that mean we have no equivalent to T-2?

In spite of the ban, there are probably jugs of biotoxins somewhere for spies to use for one-on-one killings and such. In depots around the country we have enough synthetic nerve gas to wipe out the world's population several times over, and it's just as quick as T-2. Early in the Cold War we were so enthusiastic about nerve gas that we made millions of gallons. It's been a nightmare ever since to handle and store that volatile, leaky stuff.

What is the current U.S. response to the Soviet chemical-warfare threat?

For the first time since the Nixon ban, the U.S. may soon be making chemical munitions again. Congress has already appropriated $23 million for a factory at the Pine Bluff Arsenal in Arkansas that, if more money and a go-ahead come, will build "binary" artillery shells and bombs. These would be our primary chemical offensive weaponry. Instead of a powder charge or a warhead, these so-called "binaries" carry two compartments—one for a poison, the other for an activating agent. They are mixed before impact. Because the poison is inert until then, the binaries are supposedly safer to transport than the canisters now clogging our stockpiles.

Isn't it ironic that your charges are giving the Pentagon the evidence it needs to justify increasing its own chemical warfare budget?

Because my book makes revelations about the Soviets, it's assumed I must be in somebody's pocket in the U.S. government. But I do not work for the CIA, nor am I the CIA's dupe. In fact, I am at least as critical of the U.S. as of the U.S.S.R. I've personally felt more outraged about U.S. involvements than about the Russians'—you're supposed to be able to trust your friends. I am repelled by our plans to continue chemical warfare and by our plans to continue chemical-warfare research. Here we're bitching about the Russians and yet we're doing the same thing—increasing our chemical-warfare armaments. That's the height of hypocrisy.