Leaders of the American and Soviet governments -- whatever their differences -- profess to have one common political priority this year: the conclusion of an agreement to limit strategic nuclear weapons.

Yet the United States is today launching its most ambitious nuclear weapons production program in two decades to meet what its intelligence agencies say are growing Soviet nuclear programs.

Over the next five yeras, the American nuclear stockpile is to receive: new warheads for land and sea-based intercontinental missiles: a new air-launched cruise missile: a new warhead for the 56-mile Lance missile; new strategic and tactical bombs and a whole family of atomic artillery shells.

At the nuclear weapons laboratories in Los Alamos. N.M., and Livermore, Calif., scientists have already designed and tested the next generation of strategic nuclear devices. Almost 20 candidate warheads exist for the landbased MX ICBM and submarine-launched Trident II, the weapons of the 1980s.

Furthermore, researchers at both albs are looking at new materials -- such as transplutonic elements created from plutonium -- which someday may offer nuclear explosive power with less than one-fifth the fission material now used.

Paradoxical as it may seem, it is a fundamental truth of the nuclear arms competition that both the Soviet Union and the United States spend billions each year o produce and develop holocaustic weapons whose chief value to mankind is that they never be used.

Both here and in the Soviet Union, the nuclear weapons enterprise is propelled by a rapidly evolving technology, and an action-reaction cycle between the two countries' program and the influential elite of technicians who determine, in strictest secrecy, the agenda of nuclear weapons development.

This creeping growth of nuclear destructive power will remain unchecked, even with a new strategic arms limitation treaty (SALT).

For example, the new U.S. strategic and tactical nuclear weapons scheduled for production over-the next five years will be larger yield, longer range or more accurate than the ones they replace.

Some will be three.

The public and most of Congress reamin ignorant of the numbers and capabilities of new nuclear weapons because almost all duscussions and eecisions about them historically have been the private preserve of a relatively few technocrats and scientists inside and outside government.

Some of the new weapons are:

In 1974 American weapons managers embarked on development of a warhead able to destroy Soviet land-based missiles. The decision was promped by concern that the Soviets were achieving such a capability.,

The result was the Mark 12A, a warhead that doubled the yield and accuracy of the current Mark 12. The new weapon was designed to be deployed on the existing Minuteman III missile.

The Mark 12A packs a 350-kiloton punch equivalent to 350,000 tons of TNT) compared to the 175-kiliton yield on the 550 existing Minuteman III missile, each armed with three multiple, independently targetable reentry vehicle (MIRV) warheads. The The Hiroshima bomb of 1945 was 12.5 kilotons.

A nuclear blast of 350 kilotons would knock down ordinary buildings within a three-mile radius, cause second-degree burns to those within six miles, and kill half of those exposed within a mile and a half.

A newly designed guidance system permits the warhead to travel 5,000 miles or more and land within 600 feet (about two football fields) of its target. Doubling the accuracy of a warhead, as the Mark 12A does, multiplies its destructive yield by eight times. By doubling both yield and accuracy the Mark 12A will be 16 times more effective against Soviet missile silos than the current Minuteman III warhead.

This weapon, too, represents a great leap in power and accuracy. Trident I is being produced as a replacement for the submarine-launched singel-warhead Polaris and also the more modern Poseidon MIRV missile system.

The Trident missile is designed to travel 4,000 miles, twice the range of the present sub-launched missiles, enabling submarines to hide in almost twice the ocean area present subs can use.

To get that range and still keep the Trident warhead at the same overall size as the Poseidon, scientists had to set at eight the number of warheads each Trident missile could carry. The Poseidon carries 10 to 14.

Each Tident warhead carries a 100-kiloton yield, more than double the 40-kiloton yield of the Poseidon.

The Trident I is designed for the new Trident submarines which will carry 24 missiles, although it will go initially on the 10 Poseidon submarines in the nuclear fleet.

Thus, at some time in the 1980s, just three Trident submarines will have more warheads than Robert S. McNamara once thought necessary to destroy Soviet society.

The warhead for the air-launched cruise missile reportedly will have a 200-kiloton yield and a guidance system considered so accurate it can place the missile almost directly on target.

The cruise missile is, in effect a pilotless jet plane that is programed to fly a specified route and crash into its target.

It is to be carried by a B52, giving that long-range bomber added accuracy and yield as a nuclear weapon delivery system.

For example, under published loading plans, Strategic Air Command B52s set to fly from the United States to the Soviet Union on the average are programed to carry only four nuclear bombs. That same B52 is now said to carry 20 air-launced cruise missiles - eight in a rotary device in the old bombbay and 12 attached to carrying device under the wings.

The key to the cruise missile is its guidance system, which is controlled by a computerized radar device called Tercom, for terrain contour matching.

A three-dimensional map to the target is placed in the missile's computer. After the cruise missile's release from the B52 carrier, the radar on board the missile "reads" the ground and steers it at heights 100 feet above the ground, to the preset target.

The Soviet recognize the nuclear cruise missile as a more dangerous weapon than a nuclear bomb. At SALT II negotiations, they have required that B52s with cruise missiles be counted as MIRVed weapons carriers and included within the limitation for MIRVs.

The B52 is to be counted not as a MIRV but as a missile with only one warhead.

This artillery device is one of the smallest and most complex nuclear weapons, designed for use in the west European theater against a massive tank attack from the Soviet Union and the Warsaw Pact countries. It has a short range, eight to ten miles, and must be fired behind th elines far enough in front of friendly troops to spare them heat, blast or radiation damage.

The present nuclear artillery rounds are slow-firing and not of sufficiently high yield to be militarily effective. At higher yields of 10 kilotons they would cause too much damage to surrounding civilian installations. Lower yields are not sufficiently strong to destroy tanks.

o meet this dilemma, the scientists of Lawrence Livermore Laboratory developed the neutron eight-inch shell.

While normal fission weapons get their destructive effects primarily from blast and heat, the neutron does it primarily through enchanced radiation.

Controversy over the neutron weapons caused President Carter last April to defer their production. Technology, however, has come to the rescue of the weapon.

The neutron artillery shell will have large range (up to 20 miles) and devices that would make it more secure from terrorists, should it be seized. An electronic device within it could be activated if the weapon fell into the wrong hands, with the result that some key internal parts fuse together and prevent its firing as a nuclear explosion.

Safety rather than military need may soon become the reason for replacing some of the older nuclear weapons in the stockpile.

Take, for example, the push to employ "insensitive" high explosives (IHE) in nuclear devices.

Developed initially for the B61 tactical nuclear bomb by Los Almos, IHE does not explode as easily as chemical explosives now used as triggers in fission devices. IHE would not ignite if hit by a rifle bullet or blow up if subjected to impact at high speeds.

A nuclear bomb with IHE in it, therefore, would not explode in an airplane crash.