Government scientists think they have found a way to build conventional bombs and warheads that could later be converted to nuclear devices simply by inserting a special component.
But the White House last fall delayed further development and testing of the concept pending an interagency study of its military utility and arms control consequences.
Brief references to the once highly classified "insertable nuclear components," or INCs, were contained in transcripts of Senate Armed Services Committee hearings published yesterday and arms control impact statements released last week.
INCs, one government nuclear weapons expert said yesterday, "have always been controversial." He pointed specifically to opposition from arms control experts who, he said, "believe they will have difficulty in monitoring and verifying" the presence of nuclear weapons using INCs.
That concern, other sources said, led the White House to order the pentagon to undertake its study of INCs.
"No further funds will be spent on INCs," according to the Carter administration's fiscal 1979 arms control statements, "unless the president decides to go ahead."
INCs were designed to leiminate the current necessity to have both nuclear and conventional versions of various weapons.
The concept was developed several years ago by Department of Energy nuclear weapons scientists at the Los Alamos Scientific Laboratory and adopted initially by Pentagon planners for possible use in the Harpoon antiship missile system.
In describing the INC concept before the Senate committee's closed hearing last April, Gen. Joseph Bratton, director of DOE's division of military application, said, "On shipboard where the storage space for weapons was limited, that one could have a conventional or nuclear capability by going to this technique instead of a double stockage of complete weapons."
Bratton also said that security and safety, in case of premature explosions, were considerations in the INC idea.
Along with possible use in the Harpoon system, INC "is dimensioned in connection with a number of weapons," Bratton told the committee.
The Army has several dual capable systems under study as does the Air Force.
"Some services see a logistics problem in INCs," one officer said yesterday," while otherx see benefits."
Currently, the services must maintain independent weapons dumps to maintain both conventional and nuclear bombs and warheads.
INCs, its proponents argue, would case that problem but also blur the distinction somewhat between the two categories of weapons.
White House concern over INCs developed last year in association with congressional opposition to the nuclear Harpoon. Crities led by Sen. John Culver (D-Iowa) argued that nuclear antiship missiles would create more arms control problems than they might be worth particularly since the conventional versions have adequate explosive power to destroy their targets if they are as accurate as their proponents claim.
In reviewing Culver's arguments. White House aides became concerned about the arms control implications of the INC concept, according to sources.
At that point, a decision was made to delay INC testing until the Pentagon had carefully studied both the potential military uses in mind for the INC concept and the arms control questions - if any - raised by those future weapons.
"This situation has been brewing over the years," one White House aide said yesterday. "People have shot from the hip on both sides without a thorough analysis."
A Pentagon source said yesterday the INC interagency study "is under way" but no completion date was set.
A conceptual and feasibility study of a nuclear Harpoon that would use INC as well as a standard nuclear design also is being conducted by the Pentagon.
At Los Alamos laboratories, a "low-level" advanced development affort is under way, according to DOE officials. But until the Pentagon specifies a weapons system and President Carter agrees to it, "no one is particularly enthusiastic at this time," one DOE expert said yesterday.
But he added, "It is far from a dead concept."