Before they start digging multi-billion-dollar tunnels or "shell-game" holes to hide the missiles of the 1980s, an explanation should be given for the official indifference to a far superior - and strikingly less expensive - proposal for denying an attacker the lure of fixed missile bases. The proposal in large part originates with one of the defense establishment's most widely respected and frequently consulted scientific specialists, Richard Garwin.

The proposal is this: Put the missiles on a fleet of very small, stripped-down submarines that would operate off the East and West coasts, and perhaps in the Great Lakes. Even if they patrolled only within territorial waters, they would be cloaked by a square mileage of water that would far exceed the areas now being contemplated for the land-based mobile missile. Furthermore, unlike the long-range, ocean-oging Polaris and Poseidon submarines, which are usually on their own against opposing forces, the close-in, missile-carrying craft would be within easy range of shore-based protection.

Garwin, who has long been one of the government's chief scientific consultants on anti-submarine warfare, argues that recent, but proven, developments in submarine technology make it feasible to put into service a fleet of tiny, missile-carrying underseas craft of about 400 tons each, compared to 8,000 tons for the Poseidon and 18,000 tons for the coming Trident class. Each of these, he says, could carry, strapped horizontally to its hull, two of the MX missiles now being developed for mobile deployment. Over a 10-year period, he estimates, the total cost for building the fleet and keeping 200 missiles at sea would be $17 billion, compared with an estimated $30 billion for a land-based concealment system.

The submarines would be cheap because, operating in safe waters, the could afford to be slow, and therefore could be diesel-driven or propelled by fuel cells, rather than nuclear power. They wouldn't require the elaborate navigation systems necessary for oceangoing missile submarines, since they could take their positions - both for navigation and missile-aiming - from nearby shore stations. And they wouldn't need defensive armament, since they would always be within range of friendly forces and in waters whose approach by hostile anti-submarine forces could be detected well in advance. The result, Garwin says, would be an extremely simple craft that could easily be operated by a crew of 15. And he points out that the basic hull and propulsion design for such small submarines are not a matter of conjecture: The West German navy is already operating such tiny craft - non-missile bearing, however - in the Baltic Sea.

The submarine proposal has more advantages than those of cost and concealment.

Since submarines must periodically come into port, it is easy to verify that their total missile cargo is within agreed limits, something that is difficult to do with an underground concealment system. In addition, the vastness of the ocean operating area is more likely to discourage interest in a sudden knockout attack than is a clearly delineated, land-based missile "reservation," even if the missiles are constantly in motion.

Garwin and a colleague, physcist Sidney Drell, of Stanford University, have testified in Congress about the proposed system, but without stirring much interest there or in the Pentagon, where they have also presented their case. The reason, Garwin says, is that the Air Force does not want to yield anything to the Navy, and the Navy doesn't want to give up its nuclear-powered behemoth submarines in favor of diesel-powered miniatures.

The indifference to the small-submarine proposal thus makes sense in terms of the institutional interests of those services. But otherwise it makes no sense whatever. If the idea is going to be neglected in favor of the mammoth excavation scheme now being planned, the Carter administration should explain why.