From the muddy trenches of World War I to the lofty chambers of UNESCO today, the subject of chemical warfare has long been of concern to France.

French troops were among the first victims of the deadly, yellow chlorine gas released by the Germans at Ypres, Belgium, on April 22, 1915. An estimated 5,000 men died and 15,000 others were incapacitated in what is considered the beginning of 20th century chemical war.About a month later, 6,000 more men in the trenches suffocated from inhaling phosgene gas used by the Germans on the Russian front. By the end of World War I, chlorine, phosgene and mustard gas had been established as chemical weapons.

Public revulsion at their use brought about the international agreement in 1925 banning the use of chemical and bacteriological agents.

France - which acknowledges it has the capability of making chemical weapons but has never admitted possessing them - is custodian of the 1925 Geneva Protocol, holding the original document in the Foreign Ministry and accepting additional signatories to it over the years.

Successive governments have made much of the moral responsiblity implied in serving as custodian, and the feeling was the backdrop against which President Francois Mitterrand proposed France play host to the international conference on chemical weapons that began Saturday.

Not everyone, however, saw France as the best choice for the five-day conference.

The English-language Tehran Times said Saturday that Paris was the "least qualified" to host the meeting because of its estimated $5 billion worth of arms sales to Iraq during the eight-year Persian Gulf war.

"In view of France's indirect condonement of the Iraqi regime's actions during the war and in view of the fact that Iraq is one country which flagrantly used chemical weapons . . . any Western capital would have been a better and happier choice," the newspaper said.

Both Iran and Iraq have accused the other of using poison gas. It is known that Iraq used mustard gas during the war. Both are signatories to the protocol.