AMERICANS WILL always consider the Japanese attack on Pearl Harbor on Dec. 7, 1941, the ultimate act of international treachery, a blow delivered without warning. But the prevailing Japanese view has always explained the attack in quite different terms, portraying it as a predictable response to American actions that left Japan mortally vulnerable and with no alternative but to strike.

In the Japanese view, these U.S. actions centered on oil. As in most conflicts of this war-scarred century, oil was a major factor in World War II, a precious resource that shaped everything from global strategy to theatre military operations to tactical maneuvering at the battlefield level.

A recently discovered diary from one of Emperor Hirohito's aides makes clear how the Japanese have viewed oil's importance in the Pacific war. It quotes the late emperor as saying, after the war, that Japan went to war with the United States because of oil -- and lost the war because of oil.

In fact, the war resulted from the drive by Japanese militarists to establish an empire, "the Greater East Asia Co-Prosperity Sphere," in the Far East, beginning with the absorption of Manchuria in 1931 and moving into high gear with Japan's war against China in 1937. The United States was the biggest obstacle to Japan's aims, especially after Hitler overran Europe in 1940. Oil proved to be one of the critical elements in the pattern of events that brought the two countries to war.

The Japanese military was obsessed with oil. Its strategists had carefully studied the lessons of World War I, in which oil and the internal combustion engine had proved of decisive importance. The Japanese military machine was almost entirely dependent upon imported oil -- and that meant the United States, which supplied about 80 percent of Japan's supplies in those days. (Much of the rest came from the Dutch East Indies -- now Indonesia.)

As Japan pursued its war against China, the administration of Franklin D. Roosevelt, pushed by outraged public opinion, embargoed the export to Japan of various goods of military value, beginning with a "moral embargo" against the sale of airplanes and engines, then extended to an actual prohibition against the export of iron and scrap metal and aviation gasoline of 87 octane and higher. However, Japanese planes could operate at lower octanes, and in fact Japan stepped up imports of U.S. oil. The embargoes did nothing to deter Japan's militarism.

Some Japanese leaders became convinced that war with America was inevitable. The Japanese Navy began planning a Pearl Harbor attack in 1940, more than a year before the actual strike. A number of army leaders wanted to take advantage of Hitler's June 1941 attack on the Soviet Union by seizing Siberia. Hitler himself pressed for this. But the navy, supported by other army leaders, wanted to strike south into the East Indies to assure Japan an independent oil supply. This view prevailed.

In July 1941, Japan invaded what is now southern Vietnam (then part of French Indochina) to bolster its China campaign and as a stepping stone to conquest of the oil-rich East Indies. Japan's military leaders knew this might provoke an all-out U.S. oil embargo; indeed, the only way for the United States to oppose this latest step -- short of military force -- was a full-scale oil embargo. Washington struggled over what to do, amid fears of coordination by German and Japanese militaries. The Japanese move into Southeast Asia and the Nazi sweep into Russia presented the United States with the horrifying prospect of an isolated America facing Europe and Asia dominated by the Axis. Washington froze Japan's financial assets in the United States. This effectively cut off Tokyo's ability to buy oil -- a de facto petroleum embargo. The British and Dutch did the same, shutting off supplies from the East Indies.

For the Japanese, this was the final link in what they claimed was "encirclement" by hostile powers. In fact, they had achieved their own self-fulfilling prophecy: Although it is not remembered as such by most Japanese, the embargo was brought on by four years of Japanese military aggression in Asia. At the time, the Japanese ambassador to Washington accurately summed up what had happened: "The Japanese move into south Indochina" had "precipitated" the "freezing measures, which in turn meant a de facto embargo, and had reacted in Japan to increase the tension."

Once the oil supply line was cut, time began running out for Tokyo. Without new sources, it had no more than an estimated two-year supply stockpiled at home. By early autumn of 1941, the fateful decision was made to launch all-out Asian conquest, with East Indies oil the most important target. "If there were no supply of oil," one admiral said, "battleships and any other warships would be nothing more than scarecrows."

The briefing materials for the Sept. 5-6, 1941, meetings at which the military sought the emperor's permission to attack put the matter this way: "At present, oil is the weak point of our Empire's national strength and fighting power . . . . As time passes, our capacity to carry on war will decline, and our Empire will become powerless militarily."

The attack on Pearl Harbor was intended to wreck the U.S. fleet and protect Japan's flank as it launched its huge Dec. 7-8 assault throughout Asia -- from Hong Kong and Singapore to Thailand and the Philippines. Both objectives were achieved, and soon Japanese tankers were once again transporting petroleum from the East Indies to the Home Islands. But in its third major aim -- to shatter American morale -- the attack had the opposite effect, instead galvanizing and uniting a formerly-divided nation.

That, in itself, may well stand as the greatest miscalculation irony of that calamitous day. But there were others.

Perhaps the most glaring was the attackers' refusal to launch a third strike at Pearl Harbor. The first two waves of Japanese planes had wreaked such devastation that they could have come back for a third round with near-impunity. But the Japanese commander decided against. His luck has been so great that he did not want to take further risks. As a result, the Japanese left untouched the most important and obvious Pearl Harbor target after the American warships themselves -- the U.S. Navy's supply of oil for its entire Pacific operations, held in storage tanks at Pearl Harbor. Had the planes hit the tanks, they would have virtually immobilized the U.S. Pacific fleet until additional oil supplies were shipped from California.

"We had about 4 1/2 million barrels of oil out there and all of it was vulnerable to .50-cal. bullets," Adm. Chester Nimitz, commander in chief of the Pacific Fleet, later said. "Had the Japanese destroyed the oil, it would have prolonged the war another two years."

Some U.S. officers quickly concluded that the attackers spared the oil tanks because they were about to invade and wanted the supply for themslves. The officers had their families buy sweaters, anticipating incarceration in prison camps in Japan, where it was much colder than Hawaii. But there was no invasion.

Thereafter, Nimitz's own strategy was clear -- and relentless. He and Adm. Ernest King, chief of naval operations, agreed (in the words of Nimitz's biographer) "that the primary objectives of the Allied armed forces were to safeguard their own supply lines and then drive westward in order to capture bases from which Japan's indispensable 'oil line' might be blocked." Given the Japanese military's rationale for going to war, that too stands as a lasting irony. Over the next three years, the Allies severed the "oil line" the Japanese had reestablished between the East Indies and Japan -- and thus eventually immobilized Japan's fleet and grounded its airplanes.

Daniel Yergin is author of "The Prize: the Epic Quest for Oil, Money, and Power," the new edition of which is published this month by Touchstone/Simon & Schuster. He is president of Cambridge Energy Research Associates.