CRISIS IN THE PERSIAN GULF : U.S. Chemical Arsenal Dwarfs That of Iraqis : Military: But world opinion makes remote the possibility that Bush would order its use.

For all the fear that Iraq is generating with its threat of using chemical weapons, the fact remains that the United States has a far larger and more potent supply of nerve and mustard gas at its disposal--enough, by some estimates, to kill everyone in the world 5,000 times.

U.S. delegate Stephen J. Ledogar reminded the 40-nation Geneva Disarmament Conference of this country’s capabilities Thursday, when he repeated the U.S. position that it has the right to “respond in kind” if its troops are hit by chemical weapons.

Still, the possibility of the United States turning its chemical weapons on the Iraqis remains remote, even if Iraq uses chemicals first. For one thing, world opinion likely would turn against a superpower that inflicted the torture of chemical weapons; for another, other weapons probably would work better.

“Rather than make their missile sites more difficult to operate (by disabling Iraqi troops with chemical weapons), blow them to smithereens,” suggested Gordon Burke, senior policy analyst for EAI Corp., a defense-industry consulting firm. “That would get to the point much faster.”

Using chemical weapons is a decision that could be made only by the President. However, Defense Secretary Dick Cheney said Tuesday that he “cannot conceive of a situation” in which the United States would use chemical weapons against Iraq.

The world has viewed chemical weapons with particular horror since the Germans used mustard gas in World War I, killing 100,000 and causing 1.3 million casualties. Troops sometimes woke up in their foxholes to find that they were lying in pools of the viscous liquid, which causes terrible blisters when it touches skin, Burke said. Inhaled, it can blister the inside of the lungs.

Nerve agents, developed in the late 1930s, cause the entire nervous system to break down. A lethal dose of some types could fit on the point of a pin, and a liter jar could contain enough to kill a million people, Burke said.

The United States has been building its stockpile of chemical weapons for decades. Production was halted for 18 years after former President Richard M. Nixon declared a moratorium in 1969. President Ronald Reagan began pressing for a resumption early in his Administration, citing evidence that the Soviets were adding to their chemical arsenal.

The United States acknowledges having about 25,000 tons of chemical weapons, a supply second only to that of the Soviet Union, which says that it has 50,000 tons. President Bush and Soviet President Mikhail S. Gorbachev agreed in June to begin dismantling the two countries’ stockpiles, so that neither country will have more than 5,000 tons by the end of 1992.

In recent years, America produced chemical weapons because it feared that “the Soviets might come roaring across Europe behind a cloud of chemicals,” Burke said.

But while the United States’ top priority was countering a superpower threat, chemical weapons also were becoming what analysts call “the poor man’s nuclear arsenal”--weapons available to any country with a petrochemical, fertilizer or pharmaceutical industry, according to a report by the Center for Defense Information in Washington.

Iraq is believed to have several thousand tons of chemical weapons, CIA Director William H. Webster told Congress in early 1989.

More frightening than the size of Iraq’s arsenal is its inclination to use it. About 200 civilians died during the Iran-Iraq War when both sides used chemical weapons, and Iraqi President Saddam Hussein has used nerve gas against Kurdish rebels in his own country.

Both the United States and Iraq signed the Geneva Protocol of 1925, which banned first use of chemical weapons. The talks currently under way in Geneva are aimed at a global ban, but it probably will be years before a treaty is negotiated and signed.