The Midgetman missile proposed by the Scowcroft commission, President Reagan's high-powered, bipartisan study group on strategic forces, sprang from the thinking of a small number of nuclear strategists.
If adopted, a shift to the small, single-warhead missile would represent the biggest structural change in America's strategic nuclear weapons forces in recent years. It could push arms control talks with the Soviets in new directions.
Three of the leading proponents of such a missile - Paul Nitze, Richard Garwin, and Jan M. Lodal - have occasionally been at odds over the years. But like so many other experts in the field of nuclear weapons strategy, they share some assumptions. One is that America's land-based missile force has grown increasingly vulnerable, at least in theory, to a possible Soviet first strike.
In the view of the three experts, each working in his own separate way on the vulnerability question, the Midgetman would solve the problem. Having only one warhead, the Midgetman would offer a less tempting target to the Soviets than the 10-warhead MX missile. And it could be made mobile more easily than could the MX.
The three experts are part of a mostly invisible community of nuclear weapons strategists who think about how nuclear weapons might be used to defend the United States and allied nations from attack and how the number of such weapons might be controlled or reduced.
The proposed Midgetman holds a prominent place in the Scowcroft commission's report, made public April 11. On Tuesday, Mr. Reagan formally approved the report's recommendations. A major public debate is expected to ensue.
But before that debate begins, the small community of nuclear arms experts, who have tended over the past 30 years to set the terms of debate, will have drawn many of their own conclusions. These people are the largely unseen movers and shakers who represent what one congressional staff expert on the subject calls the ''invisible empire'' of nuclear defense strategy. When not in government, most of these specialists can be found in defense industries, in law or consulting firms, or in universities and research institutes.
Many are ''switch hitters'' who can shift from a Republican to a Democratic administration with ease. They include:
* Paul Nitze, who currently is the Reagan administration's chief negotiator at talks with the Soviets in Geneva over intermediate-range nuclear missiles. He helped negotiate the 1972 treaty with Moscow limiting antiballistic missile (ABM) systems. Highly respected for his experience at top levels of several administrations, Mr. Nitze was once something of a loner in his advocacy of small, single-warhead missiles. He favors production of the MX and Midgetman.
* Richard Garwin, a physicist now with IBM and Columbia University who made the first detailed design of a hydrogen bomb. He has acted as a defense consultant to successive administrations. Well known among other experts for his technical expertise and innovative ideas - such as gravel to be thrown up as an ABM defense - Dr. Garwin has for some years advocated small strategic missiles. He supports deployment of the Midgetman, but opposes the MX.
* Jan M. Lodal, an engineer-turned-businessman who once worked as a deputy to Henry Kissinger when Mr. Kissinger was national security adviser to Presidents Nixon and Ford. He is considered one of the sharpest analysts in the capital. He was one of the experts who advised Kissinger at three US-Soviet summit meetings (Moscow, Vladivostok, and Helsinki). Now an adviser to Democratic presidential candidate Walter Mondale, Mr. Lodal championed a small, single-warhead intercontinental ballistic missile (ICBM) when it was not popular to do so. Lodal is critical of MX, but will buy it if Midgetman is accepted.
Given the endorsement of experts such as these, plus a growing number of supporters in the US Congress, one would think the Midgetman was well on its way to congressional approval. It has the potential for advancing the nation beyond the all-consuming, decade-and-a-half debate over the MX. It has something to offer hard-liners in Congress who want to see new weapons built to offset what they perceive to be a Soviet advantage in land-based missiles. But it also has something to offer ''softliners,'' whose main concern is arms control and stability, because it would be less threatening to Soviet land-based forces than the MX would.
The Midgetman concept has a forceful and articulate supporter in Rep. Albert Gore Jr. of Tennessee, a youthful-looking Democrat who has made himself one of the few true experts on nuclear weapons in the Congress. Representative Gore, who is currently assessing the presidential commission's recommendations, could hold the key to approval of them in the House of Representatives.
In Gore's view, the driving force behind the arms race is the fear that one superpower, using highly accurate multiple warhead land-based missiles, might be capable of destroying the other's land-based ICBMs. Because the Soviet Union has concentrated more on heavy, land-based missiles than has the US, the Soviets hold at least a theoretical advantage in this department. Gore proposes negotiations with the Soviets to replace the current force of multiwarhead ICBMs with single warhead ICBMs on both sides.
The Midgetman proposal has been given added respectability by former Secretary of State Henry A. Kissinger. In a Time magazine article on March 21, he proposed shifting from multiwarhead to single-warhead missiles as soon as possible. A ceiling on warheads could be negotiated with the Soviet Union, according to Kissinger. If the Soviets refused such a scheme, the US could proceed unilaterally: The final size of its single-warhead missile force would depend on the number of warheads in the Soviet force.
Although Kissinger doesn't acknowledge it, his plan appears to draw heavily on the ideas of Lodal and Gore.
One problem for Midgetman proponents is uncertainty over the Reagan administration's commitment - or that of future administrations - to the concept. At this point, the only vote in the Congress is to be for or against production money for the MX missile. No one in Congress can yet guarantee that a vote for the MX is also a vote for Midgetman.
The Scowcroft commission said it believed that a single-warhead missile weighing about 15 tons (rather than the nearly 100 tons of MX) might offer greater flexibility in the long-run effort to obtain an ICBM force that ''is highly survivable.'' It thus recommends beginning the engineering design of such an ICBM, leading to initial operating capability in the early 1990s. The deployment of 100 MXs as called for by the commission would be only an interim measure.
But what happens if the White House simply uses this recommendation to gain support for a compromise over the MX? The President could come back later with a request to expand the MX force while not really putting its weight behind the Midgetman. In order to prevent this from happening, some in Congress are thinking of attaching to the MX appropriations bills a guarantee that work on the Midgetman will proceed as quickly and efficiently as possible.
Another problem for proponents is the US Air Force: It's in charge of developing ICBMs, and is unenthusiastic about Midgetman as a possible successor to the MX.
Lodal says he thinks an argument can be made for giving the US Army responsibility for developing Midgetman, thus ''breaking down the rigid approach we've had for more than three decades.'' The Army has already had considerable experience with small missiles such as the Pershing II.
The small-missile concept has already drawn criticism from some Defense Department officials. Some say that the Midgetman could cost more than twice as much as the projected cost to deploy 100 MX missiles. The main problem, they say , is that of developing an adequately protected transporter to move the small missiles around if a decision is reached to make them mobile.
Former Secretary of Defense Harold Brown, a counselor to the Scowcroft commission, argues that ''unless the United States can negotiate severe limits on a level of ICBM warheads, the number of single-warhead missiles needed for a force of reasonable capability and survivability could make the system costs, and the amount of land required, prohibitively great.'' Mr. Brown also says that a mobile system might easily be barraged into destruction or forced into peacetime deployment on highways, thus raising political difficulties.
Roger Molander, head of a nuclear education group called Ground Zero, contends that Midgetman is simply another unworkable product of what he calls the ''priesthood'' of nuclear weapons strategists. ICBM invulnerability is an impossible goal, he says. An aeronautical physicist who once worked at the Defense Department and at the White House, Mr. Molander was a member of the elite who had access to highly classified data on nuclear weapons. Lodal, former director of program analysis for then-presidential adviser Henry Kissinger, hired Molander to work on the National Security Council staff in 1974, and Molander stayed on until 1981. Molander concedes that Midgetman might have one virtue: ''It does kind of get us out of the gridlock obsession with the MX,'' he says.