The Defense Department wants two different warhead designs -- one packing almost twice the power of the other -- to be demobile ICBM, according to informed sources.
Each MX warhead will carry 10 individual bombs -- termed re-entry vehicles -- that can be aimed at separate targets.
In one design, reportedly favored by Defense Secretary Harold Brown, each bomb would have a yield of about 335 kilotons, equivalent to 335,000 tons of TNT. The Hiroshima bomb was 12.5 kilotons.
The second design, favored by Air Force officers involved in the missle program, would have bombs packing over 500 kilotons of power.
Rather than choosing between the two warheads, the Pentagon has asked the Department of Energy to have both designs developed further.
A well-placed administration source held out the possibility yesterday that both warheads could eventually be developed on the 200 missile to be built.
At the same time it was learned that a Presidential Review Committee, chaired by Secretary Brown, met at the White House yesterday and agreed that so-called "racetrack" basing for the MX be recommended to the president for his final approval.
Carter's decision to build the giant $30 billion-plus MX missile system was announced in early June, prior to the SALT II summit with the Soviets. He postponed saying how the mobile missiles would be based until studies were completed.
Administration officials said yesterday they expected the president to announce approved "racetrack" basing early in September.
Under the concept, each giant MX would be carried on a mobile transporter-launcher around a racetrack-shaped area having cement-hardened parking shelters at 1 1/2-mile intervals.
Between 20 and 25 shelters would be built for each of 200 MX racetracks. Since the Soviets would not know which shelter housed the MX, they would have to used up an unacceptalbe number of warheads to carry out a first strike against the system, planners believe.
If the Soviets expand the number of warheads on their ICBMS, Air Force planners have suggested a mobile anti-ballistic missile system could developed to add protection to each MX "racetrack." But since a situation is not expected to develop -- if at all -- until well after 1985. The SALT II treaty now awaiting Senate ratification puts a cap on Soviet wareheads, but it expires in 1985.
Because the racetracks do not involve either tunnels below ground or holes in the ground -- as have earlier MX basing schemes -- they are expected to be accepted on government-owned land by Utah and Nevada residents in whose states the MX systems are to be located.
The move to pursue further study of two warhead designs for the MX has both political and technical overtones.
As the nation's biggest ICBM, the MX is being compared to the much larger Soviet SS18, which carries a reported 10 bombs each with a yield of about 750 kilotons.
Sources within the U.S. nuclear weapons community believe the administration may develop and eventually deploy the Air Force-favored 500-kiloton warhead design because it comes closer to approximately the power of the SS18, a fact that could prove useful in the upcoming Senate SALT II debate.