The Carter administration is considering a new missile deployment pattern to demonstrate that it can keep the next generation of land-based intercontinental ballistic missiles (ICBMs) safe from Soviet attack in the 1980s.
Such reassurance is seen by the administration as vital to winning public and congressional support of the new strategic arms control agreement President Carter hopes to sign with the Soviet Union.
Rather than settle for a single basing system for the new blackbuster ICMB known as the MX, some administration officials have concluded that this froce must be divided and deployed simultaneously in fields of decoy holes, on trucks and in planes.
Soviet land-based missiles are becoming so accurate that some analysts believe the U.S. ICBM force would become vulnerable to an attack in the early 1980s.
The MX is to be much larger than the current Minuteman ICMB, delivering a payload of up to 10 warheads that could knock out Soviet missile silos.
To provide the needed deterrence, however, the MX must be based so that it would be invulnerable to a Soviet attack. Thus, U.S. planners have determined that it must be mobile rather than fixed in a single silo.
"The threat is so complicated that we need diversification," said one administration backer of the multiple deployment shceme for MX. He said the same total number of missiles would be fielded as under a single basing system.
Defense Secretary Harold Brown has asked the White House, as part of a $2.2 billion supplemental budget request for fiscal 1979, for money to push the MX missile into full-scale development and to study the various basing options.
The Pentagon idea is to spend the next year of so assessing the various basing schemes while the missile itself proceeds toward production, and ultimately decide on one.
The Joint Chiefs of Staff favor placing each MX in a field of 20 or 80 holes and moving the missile among them covertly so the Soviets could never be sure of hitting it without firing at every hole.
Some administration officials favor putting MX missiles on trucks to give them mobility. They could be shuttled through a network of military bases in sparsely populated areas safe from traffic jams. During times of crisis, they could be transported over public highways to other bases to complicate Soviet targeting.
The third basing mode, installing the MX in jumbo jets, would keep the missiles safe from destruction on the ground - provided, of course, that the planes took off in time.
"None of these systems is an invulnerable as we felt the old ICBMs were in their cement silos," conceded one adminstration official. "But, like castles, they have had their day."
Problems posed by reliance on a single basing mode for 200 to 400 MX missiles are reduced, backers of the triple deployment said, when fewer missiles are committed to each system.
The Pentagon is also trying to save money on this new generation of land missile - which could cost up to $40 billion to deploy under current estimates - by making some parts of the MX and a new sea-based Trident II missile intechangeable.
The Trident II, like the MX is designed to complicate Soviet targeting by spreading U.S. missile submarines over larger areas of ocean. The Trident II would have a range of up to 6,000 miles.
Money for both the MX and Trident II will be requested in the Pentagon's supplemental fiscal 1979 and fiscal 1980 budgets. The Pentagon hopes to get a total of $137 billion in fiscal 1980, compared to the $126 billion it requested for fiscal 1979. The request is currently under White House review, with some officials arguing for a lesser amount as part of the administration's general effort to cut government spending.