The Reagan administration's plan for deploying the MX missile combines two of the most basic elements of warfare: concrete and confusion. But it is this simple yet untried combination that is generating heated debate among the experts on nuclear weapons and strategy.
The capsules in which the missiles are to be placed are nothing more than beefed-up fortifications - steel bars and poured concrete six to eight feet thick - designed to withstand the terrific pressures that would come with an enemy nuclear strike. By bunching 100 new ''Peacekeeper'' missiles near Cheyenne , Wyo., the Air Force hopes to create such uncertainty - and in time of war, confusion - that Soviet leaders would hesitate to launch a nuclear first strike.
Ironically, both superpowers are borrowing from each other's strong points in fashioning their strategic arsenals. The Soviet Union has made much use of US high technology to build extremely accurate intercontinental ballistic missiles. Now, according to senior Defense Department officials, the United States is using intelligence gathered on Soviet missile-silo hardening to increase dramatically the protection of American ICBMs.
Just as it did before the President's official announcement this week, the ''dense pack'' basing plan has legions of critics. Many criticize it on technical grounds, warning that the missile (now renamed ''Peacekeeper'') could not survive, let alone endure, a Soviet attack. Others say it could violate existing arms control treaties.
The basic principle on which dense pack (officially called ''closely spaced basing'') rests also is not new. This is the theory that enemy warheads, if forced to attack targets in close proximity, will destroy or throw each other off course with their own blast, radiation, and debris. Called ''fratricide,'' this phenomenon has been studied by weapons planners for years.
The Air Force says at least half of the 100 missiles placed 1,800 feet apart in a 14-by-1.5-mile array would survive a Soviet attack. Because this theory could be proved only under actual wartime conditions or with atmospheric tests of nuclear weapons (which are banned), no one knows for sure whether it would work.