The U.S. commander in the Persian Gulf has been authorized to use "non-lethal riot-control gases" against Iraqi forces in certain circumstances. This Pentagon authorization and an earlier decision to attempt to immunize our troops against biological weapons significantly increases the danger that weapons of mass destruction will be used.

Most of the world considers tear gas a chemical weapon outlawed in war by the Geneva Protocol of 1925. Many signatories, including Iraq and the United States, reserve the right of chemical retaliation if chemical weapons are used against them.So the protocol is, in effect, a no-first-use treaty.

The United States rejects even a pledge against using tear gas. In 1975 President Gerald R. Ford issued an executive order stating that the first use of "riot control agents" in war would be permissible in specific situations.

Tear gas may have the capacity to kill - in high concentrations in confined bunkers, for example. Our use of it - perhaps the mere threat of use - would hand Saddam Hussein justification for the use of mustard gas and nerve agents in retaliation.

The United States, in turn, has said it would unleash "devastating retaliation" if Iraq used chemical or biological weapons. That threat is interpreted as chemical and nuclear.

The United States, which specifically has refused to renounce the first use of nuclear weapons in war, is reported to have 400 of them in the gulf area. Disconcertingly, 45 percent of respondents in a recent Gallup Poll favored the use of tactical nuclear weapons if would save the lives of U.S. troops.

Thus, a downward spiral to mass destruction - human, environmental and social, on a scale that would make devastating oil slicks or the burning of oil fields seem trivial by comparison - may lie ahead.

The effort to immunize U.S. troops against biological arms may well be futile. It is unlikely that our leaders know what agents, whether bacterial, viruses or toxins - modified by genetic engineering or natural mutation in any of a dozen different ways - must be protected against.

The danger is that any nation planning to use a biological weapon would have to protect its own forces against it. Although we accept Washington's assurances that we no longer have anthrax stockpiles, Saddam would predictably suspect that coalition troops were being immunized against it because they may eventually use it.

Furthermore, it takes up to 18 months after immunization begins to achieve full protection. Thus, if Saddam has anthrax ready to use, starting an immunization program might lead him to use it now.

Unlike the use of chemical arms, which is relatively easy to document, assertions of the use of biological weapons would be far harder to prove or disprove. Any mass outbreaks of illness might lead to allegations, true or not, of their use.

There is no fully effective defense against any chemical, biological or nuclear arms. Chemical and biological arms threaten our own troops and the health of the people in the region, as would nuclear arms, which, with fallout, would endanger non-combatants far away. The use of any of them is likely to break the restraints on all of them.

The world seems increasingly prepared to witness such use. Barring an immediate search for alternatives to continuing and escalating hostilities, the combatants are lurching toward the trip wire.