After years of practically ignoring the use of poison gas in the Iran-Iraq war, the world is

waking up to the possibility that this indiscriminate weapon could become the weapon of choice in the Mideast and among other less developed countries."The genie has gotten back out of the bottle," Secretary of State George P. Shultz told Congress last week, "and we need to stuff it back in again" because the proliferation and use of chemical weapons is "one of the most threatening things that we see on the horizon."

Echoing this conviction, an Israeli source said Syria and Libya as well as Iraq had the "means of delivery and willingness to use" chemical weapons. That, he said, "adds a new dimension to the Israeli-Arab conflict."

The sudden surge of alarm, with senatorial demands for emergency United Nations action, was brought on by Iraq's alleged use of poison gas in genocidal attacks on dissident Kurds.

Widely seen television reports showed the sores and burns of Kurdish survivors who fled from northern Iraq into neighboring Turkey.

While Turkey professed inability to prove the refugees were gassed, Shultz told a Senate Judiciary subcommittee that the United States had what it regarded as "conclusive evidence of the use of chemical weapons" by Iraq.

Chemical weapons are most effective when loosed on untrained and unprotected people, according to U.S. Army officers.

The Kurds, neither trained nor fitted with protective clothing, would have been what Army men regarded as the most vulnerable sort of targets for such weapons.

The weapons are indiscriminate, as George A. Carver Jr., a former U.S. intelligence officer, pointed out, and thus are "effective" in situations where there is no concern for distinguishing between military and civilians - and "when the wind is blowing in the right direction" so that users themselves can avoid being killed or burned.

The main chemical weapons are "blister agents" (mustard and mustard-lewisite) and "nerve agents" (which in vapor form attack the nervous system).

They can be delivered by artillery shells, aerial bombs and airborne spray tanks. Kurds who managed to escape indicated, according to reports from Turkey, that they were enveloped in a poisonous fog dispensed from aircraft.

While there have been varying reports on the chemical weapons used in the Iran-Iraq war, Pentagon sources said the poison gas believed used against Kurds was mustard, designated HD and HT in military terms.

They said it was easy to produce - "a fertilizer plant can be converted to production overnight," one said - and it was relatively cheap.

It was said to be not unlike the gas used in World War I. Gas was never used in World War II because the allies were ready to retaliate if Nazi Germany employed it. Hitler's generals would have no part of it, Carver said.

On the other hand, the use of poison gas "has become one of the most deplorable aspects" of the eight-year Iran-Iraq war, one official said. "And it caused very little public outcry" until the Kurdish incident.

Now, the official said, there was spreading concern that Third World countries would perceive poison gas as a way to "defend on the cheap."

The Israeli source similarly lamented the lack, at least until now, of "strong public condemnation" of chemical weapons use.

United Nations inspectors concluded on seven occasions during the Iran-Iraq war that Iranians had been attacked with poison gas. The weapon apparently was used against waves of Iranian infantry and, at a critical time last spring, in Iraq's retaking of the Faw Peninsula, according to Pentagon sources.

As if to underscore Shultz's worry about proliferation, the State Department followed up his congressional testimony last week with word that Libya was now able to turn out chemical weapons in quantity.

This move was part of a new U.S. drive to stop the spread of such arms.

Washington has been demanding a U.N. inquiry into the Kurdish situation. While Shultz said this country had "compelling" evidence, he resisted several senators' calls for an emergency U.N. Security Council session now.

The investigation should come first, he said, because "the better armed you are with facts that have an international imprimatur on them, the better able you are to bring about the result we seek."