The Reagan administration, hoping to blunt opposition to its decision to start producing a new generation of nerve gas-carrying shells and bombs in fiscal 1984, soon also will propose the start of treaty talks to eliminate all such chemical weapons in all countries, according to government sources.

Such a "two-track" plan--preparing to build weapons in future years while expressing willingness to negotiate them away now--is needed, sources said, to head off the expected widespread opposition of West Europeans to what some will argue is an American startup of a new arms race in chemical weapons.

This is true even though U.S. officials hold out scant hope that talks would produce a workable treaty anytime soon.

The issue is explosive politically in Europe because the weapons are designed primarily to be based and used in NATO countries, and not the United States.

The Pentagon also has one other plan for avoiding opposition in the NATO countries to its nerve gas buildup. One of the planned new weapons will be a new binary nerve gas bomb considered so safe it will be possible to base it aboard carriers at sea.

Out at sea, administration sources explain, the new bomb, called the Bigeye, would be relatively immune from demonstrations by anti-weapons groups.

Under the binary system, two non-lethal chemicals remain unmixed until the weapon is fired. It is only then that they take on their toxic characteristics. That is why these binary weapons would be safe enough for use at sea, as opposed to those chemical weapons now in the stockpile, which are already mixed.

American justification for building new weapons is that the Soviets have modernized their chemical stockpiles while those of the United States have deteriorated. The new weapons, American officials argue, will give NATO a retaliatory capability which would deter the Soviets from using any such weapons at all.

Among other things, the Army is studying the feasibility of putting chemical warheads on its proposed new ground-launched cruise missiles.

Administration sources acknowledged last week there is little assurance that new talks on elimination of all chemical weapons could lead to a verifiable treaty before the first American weapons are built. The Soviets up to now have balked at such an approach and no satisfactory plan for inspection has yet to be developed that satisfies even Washington officials.

The opening of new talks, however, would focus attention on Soviet chemical stockpiles and at the same time show the Europeans that the United States is ready to halt its new nerve gas production if the Soviet Union would agree to a verifiable treaty that would eliminate such munitions on both sides.

The "two-track" approach to chemical weapons is similar to that already under way with another controversial set of new U.S. weapons, the nuclear Pershing II and ground-launched cruise missiles, which also are to be based in Western Europe. They already have been the target of enormous public protests in the past year.

The chemical weapons treaty talks, sources said, would be among the nations that have signed the 1925 Geneva Protocol, which include the Soviet Union. This protocol requires signers to forgo first use of such weapons. It does not prohibit them.

American officials also plan to use the United Nations committee on disarmament to discuss the issue, focusing first on the Reagan administration's contention that the Soviets have been using a toxin against Laotian and Afghani anti-communists.

The NATO governments have privately told the Americans that the new chemical weapons program could create problems for the nuclear modernization plan.

Washington officials, however, have reassured the Europeans that the steps taken so far--preparation of a plant at Pine Bluff, Ark., and fiscal 1983 money to procure equpipment and stocks for the weapons--do not automatically mean the president has decided he will go ahead with production. Under the law Reagan will have to send Congress a formal finding that he believes such a step will be in the national interest.

Officials said last week that such a finding may not be made for another year. Meanwhile, the multilateral chemical warfare negotiations are expected to get under way.

The allies have been reassured by both Secretary of State Alexander M. Haig Jr., and Defense Secretary Caspar W. Weinberger that before any decision to deploy weapons overseas is made, the country or countries where the weapons would be based will be fully consulted.