General Dynamics Corp., which last fall had custody of more than $500 million in government materials and equipment, has been allowed to retain large amounts of unused federal property for years, the General Accounting Office has found.

Government auditors, monitoring use of Defense Department materials at several plants operated by General Dynamics and other defense contractors, found millions of dollars worth of equipment missing or idle.

In some instances, because of a lack of inventory controls, government materials have been diverted to commercial contracts or resold to federal agencies as spare parts, the auditors found.

Contractors rarely have been required to assume liability for lost or stolen materials, the GAO reported to a House Government Operations subcommittee on legislation and national security. The report was made available to United Press International.

The panel, headed by Rep. Jack Brooks (D-Tex.), revealed the names of some of the contractors as a way of intensifying its four-year campaign to pressure the Pentagon to get control of its property.

The subcommittee has criticized the Pentagon for accepting the word of contractors and failing to conduct independent inventory checks on the vast amount of government materials and equipment it provides for the manufacture of weapons and other products.

A spokesman for General Dynamics had no immediate comment on the findings of the GAO's auditors.