Without public announcement, the Army ended an 18-year moratorium on U.S. production of chemical weapons yesterday and began filling containers at a remote Arkansas site with a component of the World War II-era poisonous nerve gas known as GB.

The production, which reverses a 1969 decision by then-President Nixon to stop making "weapons whose use has been repugnant to the conscience of mankind," kicks off an intensive effort by the Reagan administration to replenish America's aging, leaking stockpile of chemical weapons with a new generation of so-called "binary" munitions.

It follows a little-noticed certification by President Reagan on Oct. 16 that production of the chemical shells "is necessitated by national security interests of the United States and the interests of other NATO member nations," and would comply with environmental and safety regulations.

His statement fulfilled a requirement imposed by Congress in 1986, when after a series of bitterly contested votes, it narrowly approved funds for chemical weapons production to begin no earlier than this month.

Binary munitions are unlike the thousands of U.S. bombs and artillery shells filled with lethal chemical agents in the 1940s and 1950s. Instead, they contain two comparatively harmless chemicals that combine to form deadly gases only after being released in bombs from airplanes or fired in artillery shells.

The Army says binary weapons are safer to store and thus are more versatile. The Army claims chemical weapons are needed to deter a possible attack on NATO in Europe by the Soviet Union, which Western officials say has a larger chemical stockpile than the United States.

The Soviets, in a move to forestall U.S. binary production, announced last spring they had ceased making chemical weapons. Soviet leader Mikhail Gorbachev repeated past Soviet criticism of the U.S. binary program during his summit meeting with Reagan last week.

The start of production yesterday at the Pine Bluff Arsenal in south Arkansas is seen by Defense Department officials as a symbolically important event partly because of the Soviet criticism.

It also ends a 14-year Army battle to overcome domestic opposition and win congressional approval for more than a million binary artillery shells, each capable of killing hundreds of people within two to five minutes by attacking their central nervous systems.

Inhalation or absorption of about a drop of the GB agent causes immediate nasal congestion, sweating, bronchial spasms, wheezing, muscular twitching, convulsions, and ultimately death through paralysis and suffocation. The 155-millimeter shells can be fired 12 to 15 miles by self-propelled or towed artillery guns.

The Bigeye binary bomb, to be produced beginning next year, will contain components of a poison known as VX that is roughly twice as toxic as GB, killing more swiftly. Unlike GB, which remains lethal for less than an hour, VX remains lethal for days. Another, secret chemical killing agent will be put into binary battlefield rockets in the early 1990s, according to Army plans. Poison-filled cruise missiles are also being considered for production in the late 1990s.

Phyllis Bledsoe, public affairs officer for the Pine Bluff Arsenal, said workers began filling artillery shell canisters with one chemical component of GB at 8 a.m. The canisters were then sealed and readied for storage.

Other canisters, already filled with the second GB component, are to be loaded into artillery shells later this month at an Army munitions plant in Shreveport, La.

Congress demanded several years ago that canisters containing GB components be stored in separate states, and Army doctrine calls for adding the Pine Bluff component to the artillery shells on the battlefield just prior to firing.

The shell is designed so that the firing ruptures a thin wall separating the two chemical containers; the chemicals mix as the shell rotates on the way to the target. The shell is timed to explode above the target, releasing GB in a deadly mist.

Bledsoe declined to disclose Pine Bluff's production rate, but said it would be "limited" at the outset and increased gradually to the maximum rate next spring. She said production equipment is still being improved and modified.

Army officials said Shreveport binary shell production will also be limited until next summer.