The cruise missile, though not yet deployed, could push the United States and the Soviet Union into spending new billions on continental air defense.

If the American cruise missile proceeds from its current test status into deployment, a Soviet military official hinted recently, the Soviet Union will also build a new generation of the weapon and defenses against it.

The result of this "action-reaction," the official said, would be both sides going up one more rung of the arms ladder with no gain in security.

He rejected the argument made by some Americans arms specialists that the cruise missile deployed on both sides would enable Washington and Moscow to breathe easier because the weapon would deter war without posing the threat of a first strike.

The cruise missile is essentially a pilotless jet plane that stays within the atmosphere. It is relatively slow, taking hours to reach its target if launched from 2,000 miles away. Intercontitnental ballistic missiles, by contrast, whoosh 5,000 miles in about 30 minutes, passing through the lower reaches of space on the way.

The cruise missile, according to those who portray it as a stabilizing influence, would give so much warning that it could not be used for surprise attack. The country being attacked by cruise missiles would have plenty of time to launch its ballistic missiles.

In disputing this theory, the Soviet official said his country could not count on its defenses detecting an incoming cruise missile. He noted that the American cruise missile is small, making it hard to find with radar beams, and flies close to the earth, where "ground clutter" makes it hard to see on a radar scope.

Air Force intelligence officers confirmed that existing Soviet air defenses would have a tough time handling the cruise missile and other low-level threats like the B-52, FB-111 and B-1 bombers, which can come in at less than 1,000 feet.

They said the Soviets are moving to improve their low-level defense by working on a better anti-aircraft missile and interceptor fighter plane. A weakness of the Soviet Mig-23 Flogger interceptor according to the Air Force, is the lack of a good radar for looking down.

Air Force intelligence officers predict the Soviet Union will follow the American lead by building a warning plane with "look down" radar to cover the low-level threat. But this would be expensive.

The Air Force airborne warning and control systems (AWACS), a Boeing 707 transport plane stuffed with electronic get, [WORD ILLEGIBLE] $125.6 million each. The Air Force plans to buy 28 of them.

The Soviet official said his country, if the long-range cruise missile becomes a reality, must worry about the new weapon getting into the hands of West Germany and Chine as well as the United States. This would mean building vastly improved defenses.

Although the United States is considered 10 years ahead of the Soviet Union in cruise missile technology, Navy Capt. Walter M. Locke, director of the Pentagon's cruise missile program, said "a country that can play chess" can in time duplicate the highly accurate guidance system on the American cruise missile.

Locke said the Soviet Union already has a whole family of cruise missiles deployed and thus cannot fairly blame the United States for starting this part of the arms race. But the Soviet missiles are not as accurate or elusive as the American cruise missles now being flight tested.

If U.S. Soviet arms negotiators fail to limit the cruise missile and the Russians do catch up with American techonology, the President and Congress are bound to come under pressure to build defenses against the weapon.

Highly accurate Soviet cruise missiles on ships and submarines would threaten American costal cities and bases. Cruise missiles aboard Soviet bombers would provoke addition fears.

It would be easier for Pentagon officials to make a case for building defenses against cruise missiles than it was for them to advocate spending billions to shoot down ballistc missiles. Cruise missiles, because they are slower, are earier to shoot down.

Even though an anti-ballistic missile system required "hitting a bullet with a bullet," Congress still gave the Pentagon $5.8 billion to try it. The United States and Soviet Union both called off their ABM efforts under an arms control agreement.

An illustration of the defense trying to keep up with the offense is the current Navy effort to protect its ships with a weapon that fills the air over the ship with lead just before the missile hits.

Since historically every new offensive weapon has inspired defensive ones, there is no reason to believe this will not happen with the new generation cruise missile if it joins modern arsenals.