ON AUG. 6, 1945, at 8:15 in the morning, an American air crew dropped an atomic bomb on Hiroshima, Japan, a city with a civilian population of 245,000 people.

The bomb weighed 9,000 pounds. It was a fearful thing.

It killed outright approximately 100,000 men, women and children. Roughly the same number died later from injuries, burns and radiation. The historian John Toland has described one of the scenes: ". . . 350 young girls from the Girls Commercial School had been working in an empty lot . . . They wore blue mompei [pajamas] and jackets but no hats or fire hoods, and those who turned, curious, toward the [flash] - almost 300 of them - were instantly doomed. Twelve-year-old Miyoko Matsubara's instinct was to bury her face in her arms. She regained consciousness in unimaginable desolation - no people, no buildings - only limitless rubble. Where were her mompei ? All she had around her waist was a white cloth belt and it was on fire . . . She started to beat out the flames with her right hand but to her horror she saw strips of skin, her skin, dangling from it."

One of the American crewmen, Capt. Robert Lewis, saw the explosion from 31,000 feet. He cried out: "My God, what have we done."

They had done quite a lot, although the bomb they dropped was a "toy" compared with the 1979 models. It had a "yield," or explosive force, of 13,000 tons TNT.

Q: Will the SALT treaty reduced the number of nuclear warheads in U.S. and Soviet arsenals?

A: No. Both sides intend to build thousands more.

Our young pilots today, most of whom were not born in 1945, could fly over Leningrad some morning and with a single bomb, exploded at 8,000 feet, kill perhaps 900,000 people and seriously injure another 1,225,000. It would create winds of a velocity of 470 miles an hour - far greater than any hurricane. These winds would hurl people through the air at high speeds, smashing them into buildings. Air pressures from the explosion would strike houses with the force of 180 tons.

All that from one bomb. It would have a yield of 1 million tons of TNT and even that is not an especially large bomb as weapons are measured these days. The Russians some years ago built one with a yield of 100 million tons of TNT.

We and the Russians now have in our arsenals thousands of these weapons; their combined yield is measured in billions of tons of TNT, an explosive potential that is beyond comprehension. It is equal to several thousand tons of TNT for every man, woman and child on the face of the earth.

Another comparison: The annual consumption of dynamite in the United States for all industrial and construction purposes is 120,000 tons. A nuclear weapon of that explosive power is considered a pop-gun.

Q: Will the Russians gain "superiority"?

A: Yes, if you mean more destructive power - but the Soviet megatonnage is already larger than ours. No, if you mean the ability to prevent an American attack which kills tens of millions of Russians.

Our children have grown up with "nukes," although mine never talk about them. It's as if we've gotten comfortable with them or have simply hidden the dreadful knowledge in unused storage spaces of the mind. We have also disguised them with friendly names like Minuteman and Hounddog, or have made them into bland symbols with bureaucratic acronyms: SRAM, MIRV, MIX, SLBM, ALCM. Few of us know what the initials mean and, thus, they are not threatening.

This is true at high levels of the national government.

One of President Carter's cabinet members told his staff recently that he knew that "SALT" must be important, but he really didn't understand what it was all about. Most of us are that way. We are vaguely aware that politicians and generals and "experts" of various description are arguing about SALT. But it doesn't mean anything to us because they don't talk our language. That's what this little essay is about: SALT and human lives.

Q: How many people will be killed if these nuclear arsenals are ever fired?

A: Impossible to say, but the nuclear weapons total 14 billion tons of explosive power - that's three tons each for every man, woman and child on earth.

When World War II ended in 1945, there was only one nuclear weapon in all the world - a U.S. atomic bomb rather like the one dropped on Hiroshima.

Today, the United States has 9,200 "strategic" nuclear warheads powerful enough to destroy cities, industrial complexes, military facilities and tens of millions of people. The Soviet Union has 4,500 "strategic" warheads. They are more powerful than the American warheads and have the potential of killing - instantly - 160 million of us. The Brtish have nuclear wapons. So do France, China and India. South Africa and Israel may have them. Taiwan, Korea and Pakistan are moving in that direction.

There has been a second major change since 1945. At that time, the only way to deliver a nuclear weapon to a distant target was by airplane. Now there are Three "delivery systems" - airplanes, submarines that fire missiles from beneath the ocean and land-based missiles.

The third thing that has happened in these postwar years is a series of scientific achievements. The hydrogen bomb, far more powerful than the atomic bomb, has been invented. These new bombs or warheads are much smaller than the old ones and far more accurate; they can be hurled thousands of miles and will land within a few hundred feet of their targets. And because they are small, several of them, each guided to its own target, can be installed on a single rocket, and, thus, guided to several targets.

As these terrible arsenals have grown larger and larger over the years, people have argued that enough is enough, that since the United States and the Soviet Union can destroy one another there is no need to continue the race with death.

Robert mcNamara, in effect, made this argument a decade ago when he was secretary of defense. He had an acronym for the situation: MAD. It stood for "mutual assured destruction," which meant, simply, the ability of either the United States or the U.S.S.R. to respond to any attack in such a devastating way that no attack would be worthwhile. This was an echo of Nikita Khruschev's remark that in a nuclear war the "survivors would envy the dead."

For 10 years, "strategic arms limitation talks" (SALT) have gone on between the United States and the Soviet Union. The First agreements - "SALT I" - were reached in 1972. They included temporary limits on offensive weapons and a treaty sharply limiting the construction of anti-missle defenses on the theory that a country with an effective defense against missiles might be encouraged to start a war.

The second round of the strategic arms limitation talks (SALT II) has been under way for sex years and has produced a treaty (except for a few details) which Carter and Brezhnev are expected to sign in Vienna this month.

The treaty, which must be approved by the U.S. Senate, would achieve two major objectives.

First, it establishes ceilings on the number and type of missiles and long-range bombers each side can have. That number is 2,400 until 1981. Thereafter the number would be 2,250.

Second, it commits both countries to begin a third round talks (SALT III) which might produce further limitations on these weapons.

There are several things the treaty will not do. It will not reduce the number of nuclear warheads available to either side. On the country, thousands of new warheads will be built and added to the two arsenals.

By 1985, under terms of the treaty, the United States is likely to increase its nuclear warheads from 9,200 to 17,000. The U.S.S.R. is expected to increase its warhead stockpile from 4,500 to 9,500, and possibly to 18,000.

This will happen because more and more warheads will be loaded onto the allowable "vehicles."

Another thing the treaty will not do is to stop the development of new weapons. Each side will be allowed to develop one "new" missile and improve others. And there are no restrictions on exploration of that new frontier for was - non-nuclear weapons in outer space.

Thus, the SALT II treaty is in no sense a disarmament measure or even a reduction. It merely establishes upper limits for the present arms race.

Those who supports the treaty, including President Carter, offer three arguments.

First, any limitation on nuclear weapons is better than none, and ceilings help the war planners prepare for the worst case.

Second, the agreement is essential to stable relations, or "detente," with the Soviet Union.

Third, the agreement gurarantees that negotiations will continue (SALT III) and may lead to some form of real disarmament.

Q: What does SALT II accomplish?

A: It sets an upper limit on how many delivery vehicles each side can have - rockets and bombers.

Those who oppose the treaty come from two directions. Advocates of disarmament, such as Sen. George McGovern (D-S.D.), argue rightly that SALT II does not achieve that objective. Furthermore, they contend, the treaty actually will stimulate the arms race, with each side using treaty loopholes to build new and more lethal weapons.

The other line of criticsm comes from those who feel that the treaty freezes the United States into a position of nuclear inferiority. They believe the nations is already in peril.

These critics, such as Paul Nitze, have two principal fears. They believe that the Soviet Union already has an effective civil defense program that makes nuclear war feasible or "thinkable."

And they believe that with their new, "heavy" missiles, notably the SS-18, the Soviets may have a "war-winning" capability.

Within a few years, they say, sufficient numbers of these missiles will be in operation, ready to destroy in a single strike virtually all of the land-based missiles in the United States. That would leave U.S. Submarines and bombers, of course, to launch a devastating counterattack.

There is no general disagreement on that point among either the supporters or critics of SALT II. There is also no disagreement on the fact that United States does not now have the same capability.

The disagreements arise over the meaning of this "non-winning" capability.

Critics of the treaty have written this theoretical scenario:

In response to some political or miltary crisis, the Soviet Union fires a sufficient number of its SS-18s and SS-19s to destroy our land-based missiles. This might result in 20 million American deaths. The U.S. could retaliate with thousands or airborne and submarine-borne wmissiles. But instead of retaliating we would, in effect, surrender.

Why? Because the only targets we could hit would be cities and industrial complexes, and that would bring down on the United States mass destruction from the remaining Soviet weapons. In short, it would be better to lose 20 million than 160 million Americans.

Treaty advocates, such as Sen. John Culver (D-Iowa), reject that view. They think this "first strike" scenario is farfetched because the Soviets have no assurance that an American president would not unleash our nuclear arsenal regardless of the consequences. In short, the "balance of terror" would restrain both sides.

These intellectual games are pure speculation. No one knows what would happen in a nuclear exchange or how people - including a Brezhnev or Carter - would behave.

The important thing is that this issue of first-strike capability is irrelevant to the SALT debate.

With or without a treaty, that situation will not change in the next three or four years. Moreover, the remedies for American vulnerabiltiy - better protection of our missiles and development of our own first-strike capability - are permitted under the treaty. The same is true of the civil defense issue.

Critics of the treaty have raised another concern - verification. The United States, they argue, can't be sure the Russians won't cheat.

The president and his men disagree. They claim that satellites and other electronic gadgets can monitor every important thing the Russians are doing. Nitze tends to agree with that.

This issue, like th first-strike issue, exists whether there is a treaty or not. The intelligence needs of the war-gamers are constant, and their monitoring capabilities are probably enhanced by the treaty, which legitimizes monitoring by both sides.

The SALT debate in the Senate is likely to go for months. It will be filled with the jargon of the nuclear age - megatons, throw weights, CEPs, EMTs and all the acronyms we have invented. It will get into questions of first strikes and civil defense and foreign policy and defense policy and who is number one in the world.

Much of this will have nothing to do with the terms of the SALT II treaty. It will deal with the questions of Soviet intentions, America's place in the world and the deplomatic uses of nuclear might.

But the central facts of the treaty can be understood by any of us:

1. It is not a disarmament agreement, although it holds out an ephemeral hope for arms reductions in the SALT III negotiations which would follow.

2. It allows the United States to make up any military deficiencies it may now have and gives no new advantages to the Russians.

3. it contributes to the spirit, if not the reality, of detente, which simply means civil relationship between the United States and the Soviet Union.

Some years ago, a legislator arose in the Kentucky House of Representatives to urge approval of a bill. "This," he said, "is the best legislation you will consider this year. It don't help nobody and it don't hurt nobody."

In a cynical sense, the SALT II treaty is that kind of product. It will not lift from mankind the dreadful specter of bloated nuclear arsenals.

But it does establish the principle that at some point enough is enough. And it provides the link for future parleys at which future negotiators may decide that enough is really too much and that it is time to rid ourselves of some of these weapons.

You can't eat 14 billion tons of explosives?

Q: Does the SALT debate matter?

A: Yes, it matters. CAPTION: Picture 1, "Little Boy," Hiroshima, 1945; Graph 1, WARHEADS; Graph 2, MEGATONNAGE; Graph 3, FATALITIES; Graph 4, MISSILES & BOMBERS; Picture 2, Dying of radiation, Nagasaki, 1945