Congress has approved some preliminary production funds for a new nuclear artillery shell that can be made into a neutron weapon, but none of the money can be spent until a NATO country says publicly that it will accept the weapon on its soil.

Neutron weapons kill mainly by radiation rather than heat and blast. Defenders say this makes them more selective than are traditional nuclear weapons. Detractors say that also could make them easier to use, lowering the nuclear threshold. Partly for this reason, European governments have opposed their deployment publicly in the past.

Senate opponents of the new shell, led by Appropriations Committee Chairman Mark O. Hatfield (R-Ore.), killed Army requests for production money for the new shell in each of the last two years.

In the fiscal 1984 nuclear weapons appropriations that Congress passed Wednesday there is $50 million for production facilities, but only if the president certifies to Congress that "formal notification" had been received from a NATO country "in which such weapons are sought to be deployed."

And the president would have to name the country, said Sen. J. Bennett Johnston (D-La.), who wrote the proviso.

Hatfield told the Senate Wednesday that he still opposed production and that Congress "would have another crack at the money to build the shells." Johnston, ranking minority member of the subcommittee that handled the bill, said he "shared the skepticism on this weapon system," the cost of which he put "in the billions of dollars."

Each new shell would cost over $3 million, according to congressional sources, and current plans call for building up to 1,000. The new weapons would replace roughly 2,000 20-year-old 155 mm nuclear shells already deployed in western Europe.

The new shells would be more powerful than the old ones and have a range of 18 miles, nearly double that of the older version.

To overcome European resistance to neutron weapons, the Army is prepared to build the new projectile in two parts, according to congressional sources. A traditional nuclear shell would be sent to Europe. An insertion device, made of radioactive tritium, would also be produced so that when it is placed in the shell it would be turned into a neutron weapon.

Under the Army plan, however, the so-called tritium reservoirs would be kept in the United States.

Administration officials arguing for the weapon said that the British, West Germans and Italians privately have supported production becausethey want their new, jointly built cannon to be nuclear-capable. That new cannon is not the right size for the existing nuclear 155 mm shell.

The Pentagon already is building two other neutron weapons: the warhead for the Lance missile and an 8-inch artillery shell. These fully assembled neutron devices are being stockpiled in the United States, however, because no NATO country has agreed to have them on its soil.

Army officials appeared confident that they could get a NATO government to approve deployment of the new projectile, one source said yesterday.

With the U.S. nuclear weapons building system already overloaded, production of the new 155 mm shells likely would not begin for another five years.