FOR 40 YEARS MANY Americans, and foreigners too, have been contending that the United States never should have dropped the bomb on Hiroshima, that Japan was already so battered and beaten it was on the point of surrender. They reject the counter-argument that only use of that dreadful weapon forced the surrender and thus avoided the heavy loss of life inevitable if the planned invasion of Japan had taken place.

Because I played a small role in this matter and because, by sheer coincidence, I was flying over the initial invasion beach in Japan on November 1, 1945, the day it was to begin, I want to cite the record as I've been able to accumulate it, including some from recent digging into the National Archives.

That record, to me, is overwhelming that Harry Truman, president only four months when he made the decision, chose to drop the bomb essentially to end the war in a hurry and save American lives. In his 1955 memoirs, Truman wrote: "In all, it had been estimated that it would require until the late fall of 1946 to bring Japan to her knees." And: "General Marshall told me that it might cost half a million American lives to force the enemy's surrender on his home grounds."

On July 18, 1945, when he was at the Potsdam Conference with Stalin and Churchill and just after he heard that the Alamagordo, N.M., test was a success and after Stalin had promised to join the war on Aug. 15, Truman wrote to his wife in a letter not disclosed until 1983: "I'll say that we'll end the war a year sooner now, and think of the kids who won't be killed! That is the important thing."

On June 15, 1945, Gen. George C. Marshall, Army chief of staff, sent a message, recently declassified, to Gen. Douglas MacArthur, then planning to lead the invasion: "The president is very much concerned as to the number of casualties we will receive in the Olympic operation (code name for the first phase of the invasion) . . . This will be discussed with the president . . . "

At a meeting that took place on June 18 Marshall inquired about a MacArthur staff report that "for planning purposes" had estimated "battle casualties" for the first 90 days at 105,050 plus non-battle casualties of 12,600. MacArthur's response was to brush this aside as an "academic and routine" estimate, adding: "I do not anticipate such a high rate of loss." He went on to argue that the invasion's "decisive effect will eventually save lives by eliminating wasteful operations of non-decisive character," doubtless meaning those of his Navy rival, Adm. Chester W. Nimitz.

The general, who later would contend that by 1945 he had felt Russian intervention "had become superfluous," added that "the hazard and loss will be greatly lessened if an attack is launched from Siberia sufficiently ahead of our target date to commit the enemy to major combat."

At the June 18 meeting Marshall put the casualty estimate for the first 30 days at 31,000. MacArthur's staff estimate for the same initial phase had been 50,800.

Some revisionist historians have contended that Truman's bomb decision had an anti-Soviet cast, that it was designed to use the American monopoloy for atomic blackmail. The evidence to support such a view is certainly thin and scanty, although Truman was shortly to become a cold warrior. Others contend that the million casualties estimate was ridiculous, at best simply a typical Pentagon worst-case figure.

In a recent case study, for example, Roger Hilsman, a World War II military intelligence officer and later the State Department's intelligence chief, put it this way: "Although no one knows where he got his figures, Stimson also told Truman that an invasion . . . would cost a million American casualties, not to mention Japanese casualties." Hilsman contended that Marshall's estimate of the invasion cost was not 1 million but only 40,000. For this Hilsman relied on a 1968 book by Nuel Pharr Davis in which Davis, without giving any source, flatly stated that "Marshall estimated the cost at 40,000." I think this figure is in error.

Secretary of War Henry L. Stimson wrote in his 1947 memoirs, done in collaboration with McGeorge Bundy, that the invasion plans would involve military and naval forces "of the order of 5 million men" or more and that "we estimated that if we should be forced to carry this plan to its conclusion, the major fighting would not end until the latter part of 1946, at the earliest. I was informed that such operations might be expected to cost over a million casualties to American forces alone . . . "

Stimson called use of the bomb "our least abhorrent choice" for ending the American fire raids, lifting the blockade and avoiding the "the ghastly specter of a clash of great land armies . . . ." In his public report at war's end, Marshall wrote that "defending the homeland the enemy had an army of 2 million, a remaining air strength of 8,000 planes of all types, training and combat."

After leaving the presidency, Truman in a television interview said "it was estimated" that the initial invasion of the southernmost island of Kyushu, Operation Olympic, "would cost 700,000 men -- 250,000 of our youngsters to be killed and 500,000 of them to be maimed for life." Those figures doubtless stretch any 1945 estimate. But Truman that day also referred to another key factor in his decision: the murderous Okinawa campaign that had lasted from April 1 to June 21 and had cost 48,000 American casualties.

The key import of Okinawa in affecting the Truman decision was the mass employment of so-called suicide aircraft, known in Japanese as kamikaze. The toll on American ships by these one-way pilots had been the greatest in the Navy's history: 30 vessels sunk and 368 ships damaged including 10 battleships and 13 aircraft carriers. At the June 18 White House meeting Truman had commented that he hoped to avoid "an Okinawa from one end of Japan to the other." And on the TV program he recalled that bloody Okinawa "gave us some idea of what we had to do in order to defeat the Japanese . . . ."

A U.S. Fleet Headquarters estimate as of Aug. 9, the day the second bomb was dropped on Nagasaki, totaled the Japanese army and navy aircraft still available in the home islands as 3,669 and of these 1,115 were in western Japan, the Kyushu area. During the Okinawa assault by kamikazes the Navy had begun to include in its estimate of enemy aircraft both training and combat units because trainers were being used in battle. However, the Navy said, "not included in this estimate is a substantial number of training types which may be used for suicide attacks, especially at night."

By that time I was a military intelligence officer in the Pentagon, in charge of tracking the kamikaze units in the army air force on the basis of intercepted Japanese military messages. And the reason I was flying, with three other officers, over that initial invasion beach, at Miyazaki on Kyushu, was that at war's end I had gone to Japan where I headed an eight- man team checking up on our intelligence estimates, part of the U.S. Strategic Bomb Survey.

The Miyazaki beach, barely 30 miles long, looked like an ideal landing spot, long and gently sloping to the sea, the biggest beach on the island. But it was terribly shallow and behind it rose a range from which murderous fire on the beaches would have been possible.

My notes show that at Oita, in northern Kyushu, we found Japanese biplane trainers with bomb racks loaded for kamikaze pilots, that at Karasehara further south the now meek Japanese officers furnished order-of- battle documents to show that at war's ed they had 56,000 troops dug in with another 70,000 in reserve and that there were many planes, 850 regular planes plus 790 suicide planes, a total of 1,640 tucked into the aircraft at air strips or hillsides.

A general told me "we were figuring on 1,000 planes, special attack kamikaze type" for defense against allied landings on Kyushu. There was a gasoline shortage but some ingenious substitutes already had been used. The Japanese told us they figured we would land on Miyazaki beach -- where else, they asked?

One Japanese general, once an assistant military attache in Washington, broke down and cried as he told us how he had planned to go out with his men on a large scale suicide mission on Aug. 16. A few others actually did so after the surrender. A lieutenant colonel objected to the American use of the word "suicide," calling it a "misnomer." "The pilot," he told me, "did not start out on his mission with the intention of committing suicide. He looked upon himself as a human bomb which would destroy a certain part of the enemy fleet for his country. They considered it a glorious thing, while a suicide may not be so glorious."

I have no doubt that my Pentagon shop's estimates of kamikaze strength were fed into the weekly order-of-battle tables that worked their way up the chain of command to become a fragment of what was put before Marshall, Stimson and Truman. In 1948 Stimson obviously depended on such figures in writing that "the air force had been reduced mainly to reliance upon kamikaze, or suicide, attacks. These latter, however, had already inflicted serious damage on our sea- going forces, and their possible effectiveness in a last ditch fight was a matter of real concern to our naval leaders."

Stimson summarized: "As we understood it in July, there was a very strong possibility that the Japanese government might determine upon resistance to the end, in all the areas of the Far East under its control. In such an event the Allies would be faced with the enormous task of destroying an armed force of 5 million men and 5,000 suicide aircraft, belonging to a race which had already amply demonstrated its ability to fight literally to the death."

The last word should come from Marshall on whom the responsibility must ultimately rest for the estimates, however good or bad the intelligence work on which he had to depend. On June 11, 1947, not long after Stimson's initial account had appeared in Harper's magazine, the general, now secretary of state, ruminated with David Lilienthal, head of the Atomic Energy Commission, who recounted Marshal's comments in his diary:

"There has been a good deal of discussion about whether we were justified in using the atomic bomb . . . . One of the things that appalled me was the cost, in casualties, of an invasion . . . . Even an ill-equipped force can cost terrible losses to a landing party. To get to the plains (of eastern Japan) would have been a very costly operation, in lives. We knew the Japanese were determined and fanatical . . . and we would have to exterminate them, almost man by man. So we thought the bomb would be a wonderful weapon as a protection and preparation for landings. But we didn't realize its value to give the Japanese such a shock that that they could surrender without complete loss of face . . . What he (Stimson) said as to the considerations that were weighed is entirely true. But we missed one of the most important consequences."

It is easy now, 40 years later, to forget the passions, bitterness, hatred, the faulty intelligence, misjudgments and sheer stupidities of the war. Using the bomb, especially against non-whites, certainly has hurt the United States in the eyes of many worldwide. But even at such a cost and even at this remove, to one who had some small role in it all, it seems to have been the right choice.