HISTORY is a process of cause and effect as inexorable as a chain reaction. So the past, properly interpreted, is a guide for coping with present challenges. But it is appalling how little America's leaders knew -- or sought to learn -- about Vietnam as they began to shape the U.S. commitment to that country's salvation. And it is ironically tragic that the studies that should have been published years ago are only now appearing, a decade since the war in Southeast Asia ended in disaster.

Ronald H. Spector, a first-rate historian and the author of the recent Eagle Against the Sun: The American War With Japan, was limited by his mandate to the military side of the early U.S. involvement in Vietnam, from its faint origins during World War II until 1960, when the communist insurgency started to gather momentum. He therefore skims over crucial political and diplomatic episodes. Nevertheless, he has produced a superb book that pulls no punches as it tells the story of American intransigence, incompetence, myopia, ignorance and sheer stupidity, supported by a wealth of official documentation. The U.S. Army is to be complimented for having underwritten a candid account that hardly brightens its image (Advice and Support appeared in hardcover under the imprint of the Army's Center of Military History).

As Spector wisely emphasizes, one of the keys to America's failure in Vietnam from the outset was the naive conviction that U.S. techniques and values could be exported to a complex Asian society, and made to work. Thus Lieutenant General Samuel T. Williams, who served as chief American military adviser in Saigon through the latter half of the 1950s, showed no interest in the fundamental social, economic and political composition of the South Vietnamese force he was supposed to be molding, but considered it "simply a less sophisticated and less experienced version of the U.S. Army."

Accordingly, Williams chose to ignore the internecine rivalries and ambitions that made the South Vietnamese officer corps corrupt and ineffective, and believed instead that weapons, training and cosmetic reforms were the answer to its shortcomings. Nor did he appreciate that Ngo Dinh Diem, the president of South Vietnam, was more concerned with protecting himself against a possible coup d',etat than with fighting the Vietcong. But above all, Williams never understood that Vietnam was going through a revolution of profound and formidable scope that could not be stopped merely by guns.

Williams was not alone in his illusions, however. He reflected views that, with some exceptions, were shared as well in the White House -- and which were later to prevail during General William Westmoreland's tenure as commander of the American combat troops in Vietnam.

Spector does not deal with the Westmoreland period. Yet it is worth stressing that Westmoreland, like his predecessors, perceived Vietnam to be essentially a problem of management. In other words, he was the uniformed equivalent of a corporation executive who reckoned that bigger investments would yield bigger results. But this approach overlooked the fact that America's enormous firepower, though devastating, would not deter a determined enemy prepared to accept stupendous losses. As a consequence, the struggle dragged on endlessly, until the American public clamored for withdrawal on any terms.

It is true that Americans were unfamiliar with Vietnam prior to World War II, and even the few who visited or lived there were oblivious to its realities. John Gunther's immensely popular Inside Asia, publihed in the 1930s, devoted only two of its 639 pages to Indochina, as the French called their colonial possession of Vietnam, Cambodia and Laos. Not long before, the solitary U.S. consul in Saigon asked to be excused from sending monthly political reports to the State Department because there were "almost no political developments to report." Yet those were years of intense subliminal tension as Vietnamese nationalist movements were organizing.

American agents of the Office of Strategic Services ventured into Vietnam during World War II to assist Ho Chi Minh, whose communist-led Vietminh guerrillas were harassing the Japanese. Even so, the region was only a sideshow to the main arenas of China and the Pacific. Incidentally, the first American killed in Vietnam was an OSS man, Major A. Peter Dewey, who was ambushed by a group of Vietnamese near Saigon in September 1945. Ho Chi Minh hastened to express his regrets, assuring the United States that another such incident would occur only "over my dead body."

IN THE DEPARTMENT of "what- might-have-beens," it is usually assumed that Franklin D. Roosevelt would have blocked France's return to Indochina had he lived into the postwar years. Roosevelt, a vocal critic of French imperialism, even offered the territory to Chiang Kai-shek, the Chinese Nationalist leader, who politely declined the gift. But Roosevelt said different things to different people and, in fact, he had no firm concept for Indochina. On January 1, 1945, three months before his death, he told Edward Stettinius, his secretary of state, "I still do not want to get mixed up in any Indochina decision. . . .Action at this time is premature."

Relying on hitherto classified documents, however, Spector details the arcane maneuvers that did carry the French back to Indochina to ignite their war with Ho Chi Minh, which was to last for eight years after its outbreak in 1946. And he does a masterful job of describing how the Truman and Eisenhower administrations, caught up in an anti- communist crusade, sustained France's futile endeavor to reconquer its dominion. There were State Department dissenters like Charlton Ogburn, an Asia specialist, who warned that "we are heading into a very bad mess." But they were disregarded.

Readers, after finishing this vivid volume, may well ask why its information and insights were not available earlier, and whether their publication might have averted the Vietnam debacle. The fact is that contemporary press accounts, congressional investigations and other disclosures did signal the danger in advance. But Americans were not paying attention. So we may now claim that our government misled us. Yet we all shared the responsibility.

Stanley Karnow, author of "Vietnam: A History," was the chief correspondent for the PBS series, "Vietnam: A Television History." He is now working on a book on the American colonial experience in the Philippines.