The Army said yesterday the best way to dispose of its aging stockpile of chemical weapons is to burn them in closed incinerators at each of the eight sites -- including the Aberdeen Proving Ground in Maryland -- where they are stored.

The conclusion was contained in the Army's final environmental impact statement to Congress, latest step in the lengthy, complex process of complying with a 1985 congressional order to destroy an estimated 25,000 tons of chemical weapons averaging 25 years old.

The directive was part of an agreement, ending years of controversy, by which Congress authorized the Defense Department to begin producing a new generation of chemical weapons for the first time since 1969. Pentagon officials say the new, so-called binary weapons are safer to store. They consist of two relatively inert chemicals that are kept separate until they mix to form a lethal agent after being fired in artillery shells or dropped in aerial bombs.

The Reagan administration says the new weapons are needed to force the Soviet Union to bargain seriously for a total ban on chemical weapons.

The current stockpile of unitary weapons, in which shells and bombs are filled with nerve gases and poisons such mustard gas, are stored at Army sites in eight states.

They are, besides Aberdeen, Anniston Army Depot, Ala.; Lexington-Blue Grass Army Depot, Ky.; Newport Army Ammunition Plant, Ind.; Pine Bluff Arsenal, Ark.; Pueblo Army Depot, Colo.; Tooele Army Depot, Utah, and Umatilla Army Depot, Ore.

Army chemical weapons also are stored in West Germany and on Johnston Atoll, an uninhabited island in the Pacific. The Army recently began preparing to build the new binary weapons at its Pine Bluff arsenal.