THE World War II Allied intelligence network flashed the warning: The Axis powers were considering the use of poison gas. It was 1943, and President Franklin Roosevelt faced a gut-wrenching decision. Should the United States do the same? No, he decided.
``Use of such weapons has been outlawed by the general opinion of civilized mankind,'' he later declared. ``This country has not used them, and I hope that we never will be compelled to use them.''
In the depths of World War II, the President considered chemical weapons beyond the pale. Practical and tactical considerations may have led to the restraint, but there was also, for Roosevelt at least, a moral element that had to be faced.
For many, the presumption still holds.
``Even in the horror and brutality of war, there are certain codes that mankind does not like to break,'' says Democratic Rep. Dante Fascell of Florida.
But the taboo is an uneven one, varying among cultures, and applied differently to chemical and biological warfare.
Though both types of warfare involve the deliberate release of substances to incapacitate, harm, or kill living beings, chemical agents cannot multiply. But biological warfare agents, such as viruses and bacteria, are organisms that have the power to reproduce themselves, and thus have the potential of spreading uncontrollably.
Chemical warfare was outlawed in 1925, biological warfare in 1972, by international agreements. But neither pact has enforcement provisions. And the 1925 accord prohibits only use, not production, transfer, or stockpiling, of chemical warfare agents.
Today, biological warfare has few champions. Objections, however, are often based as much on practical as on moral grounds. On the battlefield, bioweapons are unpredictable and difficult to use. Infections, unchecked, could ravage one's own forces as well as an enemy's. Vaccines, when available, are often costly and difficult to transport and distribute.
``It's a perversion of medical science to use germs in warfare,'' says Elisa Harris, a researcher at the Brookings Institution.
Similar objections are raised against chemical weapons. But there is greater moral ambivalence on this issue than on bioweapons.
That ambivalence is reflected in the defense posture of the US. President Nixon unilaterally renounced biological weapons in 1969, before a treaty was signed, and the United States quickly destroyed its biological weapons stockpiles and closed the manufacturing plants.
The US, however, still maintains an extensive chemical weapons arsenal, which is now being modernized, on grounds that it serves as a deterrent.
While Washington hasn't fully shunned chemical weapons, neither has it embraced them. They are the only weapons the US has declared it will never use first. Moreover, using chemical weapons in war requires presidential approval; nuclear arms are the only other class of weapon that shares that distinction. The Soviet Union has similar policies.
The two superpowers are mid-spectrum on the issue. Some countries, like Britain, have renounced both biological and chemical weapons, and claim to have destroyed all existing stocks. In some regions of the world, however, chemical weapons are seen as merely another means to wage war.
Some historians say the cultural divergence on chemical warfare goes back to World War I. By some estimates, gas attacks by both sides caused more than 1.3 million casualties and tens of thousands of deaths. They also terrified soldiers, mobilized civilians in a frantic effort to stitch together rudimentary gas masks, and sent thousands of veterans home with racking coughs and damaged lungs.
But many countries did not share that experience. In some, Western abhorrence of chemical weapons is viewed as either pointless emotion or selective morality.
``For countries that don't share our history with these weapons, they ask why killing children with chemical weapons is worse than dropping bombs on them,'' a senior US official says.
But cultural differences may be only part of the explanation. Some US military strategists also wonder how one can distinguish between moral weapons and immoral ones.
``People say that coughing your lungs out in 3 minutes because of nerve agent is an immoral way of dying, while bleeding to death in 12 because your leg has been shot off is somehow better. Those arguments leave me cold,'' says Col. Robert Orton, head of the Army's chemical weapons modernization program.
Most at risk: civilians PLACING chemical weapons in a cosmic moral framework, however, risks blurring an important distinction that does set chemical weapons apart from many other instruments of destruction.
On the battlefield, it is all but impossible to protect against the blast of heavy conventional artillery, let alone the brute force of nuclear arms. To an extent, it is possible to protect against chemical agents.
Admittedly, protection for soldiers isn't absolute. In extremely hot climates, suits and gas masks can cause heat casualties. Sustained exposure to massive amounts of chemical agents can eventually overwhelm protective gear. And, of course, not every fighting force can afford protective gear.
But gas masks and protective suits are now standard issue among the developed world's armies. Some Pentagon strategists no longer argue that the efficacy of gas warfare lies in killing large numbers of the enemy, but in forcing them to do battle in confining protective equipment at a great disadvantage.
So the distinction between chemical and other types of warfare, Harvard University biochemist Matthew Meselson says, is that ``we can protect our soldiers, but we can't protect our civilians, and we can't protect others.''
Civilians are at risk, since winds can push the devastation of chemical weapons beyond the battlefield.
``In a war, chemical weapons could kill millions of innocent people. They're highly indiscriminate,'' says Jeffrey Boutwell, a disarmament expert at the American Academy of Arts and Sciences.
It is their indiscriminate nature, Meselson says, coupled with the probability that civilians will be their chief victims, that makes chemical weapons so objectionable.
That, in his view, makes them immoral.