Armageddon - is unlikely

The first elements of the new round of American intermediate-range missiles have arrived in Italy and West Germany as well as in Britain. The Soviets have declared that they will respond in kind. Informed quarters in the West do not doubt that the Soviets will do precisely what they say they will.

Hence East and West in the power world enter into a new chapter in their relations. The new round involves the ability of each side to throw more nuclear weapons into the territory of the other.

The difference is in degree, not in kind.

Nothing is new about the United States having the ability to send nuclear missiles into Soviet territory. The US has had that ability since 1945. The Soviets have had the same ability in reverse since 1949.

The main difference is in numbers of weapons involved and the lower costs of the new weapons.

Until now the Soviets could deliver nuclear blows on targets in the US primarily by means of land- or submarine-based intercontinental ballistic missiles. Both are hideously expensive.

Until now the US could deliver nuclear blows on targets inside the Soviet Union primarily by land- or sea-based ballistic missiles, or by carrying nuclear bombs by means of long-range strategic bombers. All three methods of delivery involve extremely expensive paraphernalia.

Cruise missiles, to be used from Britain, are the cheapest way yet of moving a nuclear warhead from one country to another.

The new US cruises to be used from Britain and Italy have a range of about 1, 500 miles. Pershing IIs to be used from West Germany have a range of about 1,200 miles. The Soviet SS-20s, which the Soviets already use in Europe and will, presumably, use in their response to the new US weapons, are rated at a range of 3,100 miles.

All of these new intermediate-range weapons are mobile. This is one reason they are relatively cheap. They do not require expensive holes in the ground lined with steel and concrete, or placement in supersubmarines.

Since the new US missiles being mounted in Western Europe would be able to reach almost to Moscow and easily reach Leningrad, Minsk, Pinsk, Kiev, and Odessa, it is assumed that the Soviets will respond in kind. That means they will presumably deploy SS-20s in Siberia capable of reaching Alaska and some northern parts of the rest of the US.

They can mount their own version of the cruise missiles on ships, either of the surface or submarine variety. Also, they could mount SS-20s in submarines. The logical expectation is that they will want, in addition to their existing arsenal of strategic weapons aimed at the US, the number of new intermediate weapons equal to those the US could use against Soviet targets.

So the net effect will be to add 476 new missiles to the number the US already has which can hit targets in the Soviet Union, and the same number to those in the Soviet arsenal which can hit US targets.

Since each can already hit the other with nuclear blows in the thousands, the extra 500 on each side are enough to make the rubble bounce some more, not add significantly to the ability of each side to deter.

But it is enough, particularly when the deployment comes just when most of us have been reminded by the TV movie ''The Day After'' of the damage such weapons can do, to make a lot of people wonder whether these new weapons mean a rising danger of war between the US and the USSR.

The reasonable answer is that the extra deployments make little if any serious difference in the likelihood of war. They are not going to change significantly the ''balance of terror'' which itself is the main deterrent to war. They have not interfered with such routine things as the daily movement of American grain to the Soviet Union or work on the pipeline carrying Soviet natural gas from Siberia to Western Europe.

One hopes that the increase in the number of such weapons in the East-West balance will stimulate the diplomats to greater effort to avoid those incidents that could produce a crisis. The greatest danger of course is in the Middle East , where Arabs and Israelis commit mayhem upon each other daily using weapons that one side gets from the US and the other from the Soviets.

The main difference the new weapons make is to add to the burden on the taxpayers on both sides. The deployment of them does not in itself produce a crisis in East-West relations. It should stimulate thinking about ways and means to reduce this proliferation of redundant weapons.