Defending the continental United States against enemy attack has always been the bottom-line objective of US military policy. But how to do this has largely been left up to the imagination.
Until March of 1983, that is, when President Reagan unveiled his Strategic Defense Initiative (SDI).
Dubbed ''star wars'' by some, the SDI defense plan is intended to develop antiballistic-missile technologies that would enable the United States to destroy incoming enemy missiles before they hit their targets.
Some Pentagon analysts now believe SDI could drive the Kremlin away from reliance on land-based missiles and back to reliance on older-line weapons like bombers.
This should be good news. But it isn't. Because the US is no better prepared today to defend itself against enemy aircraft and cruise missiles than it is to stop ICBMs.
The US Air Force fields just 90 active-duty interceptors, organized into five squadrons - some 100 fewer aircraft than were stationed at Pearl Harbor in 1941.
Four of these squadrons are equipped with dated F-106 and F-4 interceptors. Only one squadron (18 aircraft) is equipped with the modern F-15 interceptor.
Provided the US received adequate warning of an impending attack, an additional 170 Air National Guard (ANG) F-106s and F-4s would be available for defense of the continental US. But even when these aircraft are included in the equation, each American fighter would be required to defend more than 20,000 square miles of territory - an area roughly the size of West Virginia.
According to the Defense Department, US surveillance systems would have difficulty detecting bombers flying at low altitudes or penetrating gaps in radar coverage. Air defense weaknesses were illustrated when in 1969 a Cuban fighter - previously undetected - landed at Homestead Air Force Base in Florida, and in 1971 when a Cuban defector flew unchallenged across the Gulf of Mexico to land in New Orleans.
By comparison, the Soviet Union deploys some 2,500 fighter-interceptors for the air defense of its civilian population and military assets. Even Cuba, whose small size belies its strategic significance, deploys over 200 interceptors and 212 surface-to-air missiles.
The US, however, has no surface-to-air missiles backing up its obviously porous air defense force.
What is there to defend against? According to Western intelligence, the Soviet Union has 150 or more TU-95 ''Bear'' and MYA-4 ''Bison'' long-range bombers, comparable in age to the American B-52 (which is being converted by the US from a penetrating bomber to a cruise missile launch-platform in response to Soviet air defenses). The long-range attack power of the Soviet Union also includes an additional 230-plus ''Backfire'' bombers which have all been deployed since 1974. A new bomber, the ''Blackjack'' - comparable to the American B-1 - is expected to become operational before the end of the decade. And production has begun on a modified TU-95 Bear, which will be used for cruise missiles. The Blackjack and Backfire bombers could be used as conventional bombers or as cruise missile carriers.
It would be foolhardy to ignore the Soviet Union's long-range cruise missile carriers. In fact, neither the aircraft nor the missiles can now be detected by US satellites, because of their low heat emission. One cruise missile, the Soviet AS-X-15, has an effective range of 1,000 miles, permitting the Soviets to attack American command, control, and communications facilities from as much as 800 miles beyond the US defense perimeter. Such an attack would help ensure that our retaliatory response was not timely, proportionate, or coordinated. The Soviets are currently deploying or developing six new cruise missiles in addition to the AS-X-15.
In marked contrast to the US, the Soviet Union has deployed more than 12,000 surface-to-air missiles as part of its comprehensive air defense, a posture that is being substantially improved with the deployment of newer, more sophisticated SA-10 and SA-12 interceptor missiles, capable, the Soviets believe, of intercepting American cruise and Pershing II missiles.
Aviation Week & Space Technology estimates that by 1987 the Soviets will have enough surface-to-air missiles, ballistic-missile radars, and fighter-interceptors to destroy 17 to 20 percent of any US strategic weapons surviving a Soviet first strike.
To be effective, the President's Strategic Defense Initiative must offer a realistic prospect for defending against the variety of threats we face, whether ballistic and cruise missiles or aircraft.
The Air Force plans to modernize the Distant Early Warning (DEW) line, update its interceptors, and construct new ''over-the-horizon'' radars. Let's hope these efforts don't share the fate of Reagan's strategic modernization program - the subject of partisan debate, delay, and deferral. Too much is at stake.