TROUBLED DAYS OF PEACE Mountbatten and Southeast Asia Command, 1945-46 By Peter Dennis St. Martin's. 270 pp. $37.50

ON A HOT September morning in 1945, an American transport crowded with troops returning from China stood out of Colombo harbor and passed close aboard another troopship flying the Union Jack. Aboard the American ship was a young GI, Chester L. Cooper. Twenty years later, in his book on the Vietnam War, Cooper vividly recalled the scene. " 'Where you going?' a Cockney voice demanded over the short distance of intervening water. 'Home,' came the answer from a thousand GI's. 'Where y'all headed?' boomed a GI. 'Saigon' was the answer from a battalion of Britishers. 'My God,' the sergeant standing next to me at the rail whispered. 'The war started for them six years ago and they can't go home yet!' " Peter Dennis' Troubled Days of Peace is a look at the confused and tragic events in Indochina and Indonesia that kept British troops at war in Southeast Asia long after the surrender of Japan.

Dennis' focus is on Southeast Asia Command and its colorful and outspoken leader, Lord Louis Mountbatten. At the Potsdam conference toward the close of the war with Japan, the geographic area of Mountbatten's command, already vast, was made still larger, so that on V-J day it comprised virtually all of Southeast Asia save the Philippines and the northern half of Indochina. When the war ended, all of Southeast Asia Command's areas, with the exception of Burma, were still under the control of large, well-armed Japanese military forces. No Allied armies had set foot in Indochina, Malaya or the Netherlands Indies since 1942. The peoples of Vietnam and Indonesia, having seen their colonial masters easily defeated by the Japanese -- in the case of the Dutch -- or intimidated, reduced to puppets and finally deposed -- in the case of the French -- were in no mood to resume their old subordinate status. In both countries there were articulate, well-organized and well-armed (with Japanese weapons) nationalist movements prepared to fight for independence and determined to have it at all costs. And while the colonial peoples had become stronger, their old masters had grown weaker. Neither the French nor the Dutch had sufficient military forces in the Far East in August 1945 to forcibly reoccupy their colonies. Only the British were in a position to help the Europeans try to regain their pre-war position in Southeast Asia.

MOUNTBATTEN'S mission was to effect the surrender and disarmament of the Japanese, to aid and repatriate Allied prisoners of war and internees and to maintain law and order pending the return of the French and Dutch. Drawing on his extensive research in British, American, French, Australian and even Dutch archives and private papers as well as interviews with key participants, Dennis makes clear why such a mission was doomed from the start.

In Indonesia and Southern Vietnam, British soldiers were soon involved in armed clashes with nationalist forces. On Java the stubborn and ill-informed actions of the Dutch probably made this inevitable despite the best efforts of Lt. Gen. Sir Philip Christison, the British commander. In Saigon, where the independence forces were weaker, more divided and more willing to negotiate, fighting was precipitated by the ill-considered pro-French actions and attitudes of Maj. Gen. Douglas Gracey, Mountbatten's commander in Indochina. Gracey and his apologists later claimed that he was only carrying out his orders and had no desire to intervene in local political controversies. Yet Dennis' book remorsely documents how Gracey's inconsistent and one-sided actions actually helped to make his mission more difficult.

Dennis shows us a British government torn between its loyalties to Dutch and French allies and its growing impatience with their reactionary and unrealistic policies in Asia, policies that complicated Britain's own attempts at orderly decolonization in Burma and India. Mountbatten, the man on the spot, was concerned to pick his way through the political minefield, well aware that he had far too few troops to pacify Southeast Asia forcibly. The moral and political pressure to return what troops he did have (mostly British and Indian Army units) to their homes after five years of war was almost irresistible. At one point, when it looked as if heavy fighting were about to break out between armed Indonesians and British forces in Batavia, Mountbatten "insisted that Indian rather than British troops be used -- 'he did not want British troops widowed at this time so long after the war.' " To which one of his officers replied, "Sir do you really think it is different if Mrs. Poop Singh is made a widow?"

Within a few weeks of the Japanese surrender, the British were obliged to call upon Japanese troops and police to help maintain order and protect Europeans in Southeast Asia against local nationals. "If there is anything that makes my blood boil," General Douglas MacArthur exclaimed, "it is to see our Allies in Indochina and Java deploying Japanese troops to reconquer the little people we promised to liberate. It is the most ignoble kind of betrayal."

In the end, of course, the "little people" refused to be reconquered and the irresolute, indecisive and distracted policies of the British and American governments may simply have added to the bitterness and distrust on the part of both Asians and their former colonial masters. Troubled Days of Peace is a judicious and thorough account that in some ways supplements, and in other ways provides a corrective to, such earlier works as Philip Ziegler's biography of Mountbatten. With its measured pursuit of political and military committees, studies, memoranda and messages, Dennis' book hardly makes for exciting reading. But if you wish to know how and why World War II spelt the doom of European colonialism in Asia, this is a good place to begin.

Ronald H. Spector, director of the Naval Historical Center, is the author of "Eagle Against the Sun: The American War With Japan" and "U.S. Marines in Grenada."