It has been said that the dust from exploded beliefs makes a fine sunset. One result of the Falklands episode may be a fine sunset from exploded beliefs about military, especially naval, forces.

In 1919, people were shocked by the title of a book: "The First World War." Fifty-three years and at least as many wars later, it is widely and strangely believed that "force settles nothing"-- although since 1919 force has settled the fates of Hitler, South Vietnam and many other things. Force--Argentina's use of it, Britain's threat or use of it-- will settle the Falklands' fate, one way or another.

Old attitudes and supremacies have vanished. (Communiqu,e to the Admiralty, 1915: "We shelled the Turks from 9 to 11: and then, being Sunday, had Divine Services.") Britain probably cannot soon recapture the islands by amphibious landings. A force coming ashore should have a substantial numerical advantage--perhaps as much as four-to- one --over the force on shore. Britain's force would be at best one-fourth that of Argentina's.

The Argentine force cannot be starved out. Mutton three meals a day is tiresome, but war is hell. So is stalemate in winter at a latitude comparable to northern Newfoundland. Britain's fleet is arriving as winter is arriving, and winter means 80-knot winds and 40-foot seas.

But Britain has nuclear submarines. Such weapons have never been used in war, so few people know how excellent they are. Those who know are those who use them 24 hours a day, 365 days a year, in undersea operations shadowing and being shadowed by Soviet submarines. They are so fast and quiet and superbly equipped that Britain's could confine Argentina's navy to port, or the seabed. The mere announcement of a blockade would cause maritime insurers to suspend policies on ships entering the area. Commercial traffic would stop; grain once destined for Russia might rot on the docks.

This is a moment to explode the belief that the use of naval forces for political objectives--"gunboat diplomacy" is the preferred epithet--is an anachronism. And it is time for renewed appreciation of the role of naval forces in the U.S.-Soviet balance.

The Soviet navy is quantitatively superior and is gaining qualitatively, but you do not accurately gauge a navy's adequacy by comparing it side-by-side with an adversary's navy. You measure a navy against its mission, as defined by geopolitics, including treaties.

The Soviet Union spans the Eurasian land mass, and is contiguous with its principal "allies." The United States is an "island nation" whose trade and alliances reach across water, on which the United States must be able to project force.

Navy forces must be designed for survival--for winning a fight, if necessary-- in high-threat areas. Such areas are increasing; the Straits of Florida is one.

The Soviets have placed in Cuba their most advanced surface ships, diesel submarines, and MiG13s. If war began in Europe, more than half the men and materiel to resupply U.S. forces would have to pass from Gulf ports through the Straits of Florida, or elsewhere through the Caribbean, within range of the formidable interdiction forces based in Cuba. Furthermore, key East Coast naval facilities-- Charleston, S.C., Mayport near Jacksonville, Fla., and Kings Bay, the new Trident base in south Georgia--can be blocked by diesel submarines operating from Cuba.

In the Mediterranean, Libya's Qaddafi has more than 300 of the finest French and Soviet aircraft. U.S. oil imports come through a "tanker pipeline" from the Persian Gulf-Indian Ocean area.

Furthermore, the Navy has less need than the other services have to simulate war. Its submarines maneuver constantly against Soviet submarines. Soviet surface ships operate a few hundred yards from U.S. maneuvers, and U.S. ships are similarly assertive around Soviet maneuvers.

The Navy is, rightfully, the biggest beneficiary of the president's rearmament plans. Its budget is doing well in Congress, not because Congress enjoys spending for military procurement, but because there is no blinking this fact: the Navy--the number of ships and the number of carriers--has been cut in half in the last 12 years, and now is inadequate for U.S. commitments.

The United States has treaty commitments to more than 40 partners, touching every ocean. The commitments can not be fulfilled with today's fleet of fewer than 500 ships. As John Lehman, secretary of the Navy, says of these commitments: "We (in the administration) didn't go looking for them. They were handed to us as the law of the land."