The United States, Britain, France and West Germany are negotiating to build together a new rocket that could knock out tanks without relying on the controversial neutron warhead.

An update of a Soviet weapon of World War II, the rockets would be set up in batteries of 12 tubes each. They could be launched from the backs or trucks or armored vehicles against tanks some 20 miles away. Each rocket would carry about 600 pounds of non-nuclear uxplosive.

Pentagon officials confirmed yesterday that cooperative development and production of the rockets to combat the Soviet tank threat is under active discussion by NATO defense leaders.

William Perry, Pentagon research director, is expected to discuss the rocket project during meetings of the Conference of National Armament Directors in Brussels this week.

After President Carter postponed his decision on whether to produce the neutron warhead for U.S. forces stationed in West Germany, Defense Secretary Harold Brown said there were alternatives to that nuclear weapon for offsetting the Soviet edge in tanks.

The multiple launch rocket system, as it is called, is but one of several alternatives to the neutron warhead, defense officials said, but a highly promising one.

The first generation of the rocket would fall free like an artillery shell. But later versions, as envisioned by weapons designers, could have guidance inside each warhead for pinpoint accuracy.

Currently, Boeing and Vought are working on designs and test models for the U.S. Army. If current negotiations succeed, firms in Britain, France and West Germany will join in the development and production program.

Specialists said the advantages of this rocket are that it has more killing power than in artillery shell, is easy to move around the battlefield and set up for accurate firing, and is easy to produce and maintain.

Although it is too early to say how many would be produced, one estimate was up to 30,000 rocket tubes under a $4 billion to $5 billion program. But Pentagon officials said they doubted the program, if approved, would be that estimating a cost of $1 billion or $2 billion.

The interest in this rocket artillery underscores the heavy NATO emphasis in Carter's defense budget, in which weapons for land warfare in Europe were generously funded. The uncertainty over whether NATO forces will receive a neutron warhead, considered especially lethal against Soviet tanks, has given such non-nuclear antitank weapons added impetus.