Existing priorities in US defense spending and the planning on which overall US military strategy is based are likely to be challenged as a result of the lessons already learned from the Falklands war.
The central theme of US defense planning for modern warfare has hitherto been heavy firepower. But the Falklands war has now shown that:
* Small and precisely guided missiles, properly used, can destroy big and expensive targets.
* Tactics can be as important a factor as concentration of firepower -- sometimes more important -- in air, sea, and land battles.
These are the conclusions of Kosta Tsipis, codirector of the program in science and technology for international security in the Department of Physics at the Massachusetts Institute of Technology.
He hopes they will open up debate within the US defense establishment about a revision of basic concepts in the light of the British and Argentine experience in the current hostilities.
Dr. Tsipis cites as evidence warranting his conclusions the sinking of the British destroyer HMS Sheffield. This was achieved with a single, relatively small French-built Exocet missile, fired from an Argentine aircraft which did not even have to come in directly over its target. The Exocet skims just above the surface of the ocean like a flying fish and this impedes its early detection by radar.
(The US, incidentally, has a missile of its own comparable to the Exocet. It is called the Harpoon and is equipped with radar more sophisticated than that in the Exocet.)
Dr. Tsipis says the destruction of the Sheffield proved: first, the effectiveness of a single missile accurately guided by its own radar to its intended target, and second, the vulnerability of the target if those manning it are not alert or prompt enough to employ the tactics to avoid being hit.
The British aboard the Sheffield, Dr. Tsipis says, must have known that the Argentine Air Force had Exocet missiles and was capable of using them. The Sheffield should therefore have had its appropriate radar warning turned on to detect the Exocet's own radar signal the moment the missile was launched and thereupon to fire ''chaff'' in the missile's direction to divert it from its intended target.
''Chaff'' is thin strips of metal fired from small-caliber guns to deflect the radar waves of a missile from a target it is intended to home in on. The Israelis have developed the use of ''chaff'' to a fine art and used it effectively when their gunboats clashed with Syrian gunboats in the 1973 Arab-Israeli war.
Dr. Tsipis puts in the same category as the sinking of the Sheffield, the sinking last week of the British frigate Ardent by Argentine planes (although whether with an Exocet or some other missile or combination of missiles is not established.)
He emphasizes the need for proper use of these small guided missiles by well-trained personnel. Training demands a big enough reserve of the missiles to permit use of them in practice. And that in turn demands that the missiles be cheap enough to allow them to be so used -- although ''cheap'' these days usually means thousands of dollars apiece. The Exocet, for example, costs $200, 000 apiece.
The Argentine successes with air-to-sea missiles suggests that the Argentine Air Force at least has had enough of them (if not of Exocets) to have permitted its flight personnel to learn to use them properly before going into battle with them.
But at the same time, Dr. Tsipis adds, the Argentine Air Force is in dual trouble. The range of its aircraft barely allows them to reach the Falklands from the mainland to attack the British forces on and around the islands. And the rate of attrition of their planes under British anti-aircraft attack is one that cannot be long sustained.
That rate of attrition, he says, is proof of the tactical skills developed by the British, on their side, in the use of relatively cheap and simple missiles by their ground forces. The simplest of these is the Blowpipe missile, hand-carried and fired from a launcher on the shoulder. More sophisticated and more costly is the Rapier missile being brought ashore on the British beachhead - and proving the vulnerability of aircraft over the battlefield itself.
In contrast, Dr. Tsipis says his impression is that the Argentine land forces on the Falklands are ill-trained, ill-equipped, and ill-commanded. They seem to be basing their defenses on a garrison situation, which should make it all the easier for the British to force their collapse under increasing pressure.
As for the Argentine Navy, it has been effectively neutralized by the presence offshore of British hunter-killer nuclear submarines armed with standard, but very sophisticated, wire-guided torpedoes. The Argentine cruiser General Belgrano was sunk by two of these torpedoes.
The British nuclear submarines are very quiet and difficult to detect. This, combined with the sophistication of their torpedoes, is keeping most of the Argentine Navy close to the mainland (or in port) and away from the operational zone -- now defined by Britain as more than 12 miles from the mainland.
The US Navy has torpedoes that are even more sophisticated than those used by the British. These US weapons use an advanced guidance method combining wire-guidance with acoustic-homing.
When it comes to the future course of the battle on the Falklands, Dr. Tsipis wonders whether the San Carlos beachhead may not have as its main purpose the provision of a base for aircraft and helicopters on West Falkland. The terrain in the 40-60 miles between San Carlos and Port Stanley, the capital and site of the main Argentine troop concentration is so difficult as to raise questions about the effectiveness of an overland advance from one to the other.
Dr. Tsipis says he is guessing, but he would not rule out an even bigger British landing than at San Carlos within days and much closer to Port Stanley and perhaps south of it.