Britain, West Germany and Italy, which have publicly refused deployment of U.S. neutron weapons on their soil, have asked the United States to produce a new 155-mm neutron artillery shell, according to testimony given Congress earlier this year.

The three European allies want the United States to build this smallest of the controversial new generation of short-range, battlefield nuclear weapons so that the FH70 cannon being developed by the three "can be nuclear-capable," according to Herman E. Roser, assistant secretary of energy for the nuclear weapons-building program. A declassified transcript of his remarks on March 8 in a closed session of a House Appropriations subcommittee was released last week.

A congressional source said Friday that the Reagan administration has been telling Congress recently that the three nations "are depending on us to come forward" with the new nuclear shell "because the old 155-mm nuclear shells don't fit in their new cannon."

The three now have older, U.S.-made guns that can fire the almost 20-year-old 155-mm nuclear shells stockpiled in Europe.

The warheads are under control of U.S. Army custodial teams and cannot be turned over to other nations for use without specific authority from the president of the United States.

Under NATO agreements, the United States will not release nuclear warheads for use in Europe without permission of the nation from which the warheads would be fired.

Neutron weapons are small hydrogen bombs that produce radiation as their primary kill mechanism, theoretically causing less damage away from the immediate battlefield than older nuclear shells whose main energy output involves blast and heat.

As with other neutron weapons, the Europeans want the new shells stored in the United States until the military situation requires them, or the political situation allows them to be transported to Europe, according to government sources.

The administration is launching a new push for congressional approval of the 155-mm shell, the third type of neutron weapon and one it plans to acquire in the largest numbers. Of the first two types, both rejected by the three allies, about 300 Lance missile warheads have been built and stored, and production of about 1,000 8-inch neutron shells is under way.

Last week, the Office of Management and Budget sent congressional Appropriations committees an amendment to the fiscal 1984 budget request adding $47.5 million to help prepare for production of the 155-mm shell. In its letter, according to congressional sources, the OMB said the neutron shell is being produced "for eventual deployment in Europe."

For the last two years, Congress has turned down production funds. One sticking point has been the cost--more than $1 million apiece--and another is growing congressional opposition to short-range battlefield systems that Europeans do not want stored or used on their territory.

The buildup of new short-range neutron weapons comes as NATO is preparing to announce a unilateral reduction in its European stockpile of more than 6,000 older nuclear battlefield weapons.

After four years of study, a NATO defense subcommittee recommended that as many as 1,000 stockpiled nuclear anti-aircraft warheads and atomic demolition munitions be retired. In addition, the group is studying ways to reduce the almost 3,000 155-mm and 8-inch nuclear shells in Europe.

Short-range, neutron battlefield weapons are one part of NATO's controversial nuclear modernization program. The other weapons are the U.S. medium-range Pershing II and ground-launched cruise missiles. Deployment of both is to begin in western Europe in December.

These missiles, which could hit targets in the Soviet Union from bases in Britain, West Germany and Italy, have drawn vocal opposition and threats from the Soviet Union. But they also have induced the Soviets to negotiate on eliminating or limiting them.

Neutron weapons, although the object of Soviet propaganda since 1977, never have appeared to bother Moscow seriously. An offer in 1978 by President Carter to halt neutron production in return for Soviet tank reductions in Europe never drew a direct response.

Last week, the House Appropriations Committee, anticipating the OMB letter, added the $47.5 million to the Energy Department's fiscal 1984 appropriations bill. The Senate Appropriations Committee, which has deleted the money for the 155-mm neutron shell for two years, has not acted on OMB's request.

Although proponents of neutron weapons say that these arms would be less destructive than currently deployed nuclear shells in western Europe, European public opinion has been strongly opposed to them.

As a result, the Reagan administration, which began production in 1981 of neutron 8-inch shells and Lance warheads, has been forced to stockpile them in the United States.