Albert Speer, 76, the administrative genius who directed German industry during World War II and the only close associate of Adolf Hitler to acknowledge personal responsibility for the atrocities committed during the Third Reich, died yesterday at St. Mary's Hospital in London.

The cause of death was not immediately reported. The Press Association, Britain's domestic news agency, said Mr. Speer was hospitalized after suffering an apparent stroke at the hotel where he was staying.

Mr. Speer, an architect by profession and an intellectual all of his life, joined Hitler in 1931. For the next 11 years, he served as the Fuehrer's architect, as a confidant on cultural matters in general, and, by his own account, as the German leader's only real friend. Among other activities, he organized the spectacular lighting effects that turned the rallies at Nuremberg in the 1930s into "cathedrals of light."

From 1942 until the end of the war in 1945, he was the absolute ruler of the German economy. He put it on a full-scale war footing. He was able to increase production even at the height of the allied bombing offensives. Among the means he used was slave labor.

In the last year of the war, he repeatedly urged Hitler to seek peace. In the final months of the conflict in Europe, he was the only member of the inner circle who openly resisted Hitler's orders to destroy what remained of his country as the allies advanced.

At the Nuremberg war crimes trials, he alone among the defendants admitted war guilt. He was sentenced to 20 years in Spandau prison in Berlin. While there, he made notes for two of the most remarkable books ever published about the Nazi era. They are "Inside the Third Reich," which appeared in Germany in 1969 and in the United States a year later, and "Spandau: The Secret Diaries," which appeared in 1975 and 1976.

Through his personality, his career, and -- most importantly, perhaps -- through his books, Albert Speer provided insights of enormous value into the how and why of Hitler and his movement. For if Albert Speer was himself an educated and civilized man, how could he follow the demonic Hitler? How could an educated and civilized man knowingly use slave labor, the specific crime of which he was convicted at Nuremberg? How could one who was so close to the leader finally defy him? And, finally, why was Albert Speer the only German of his rank to acknowledge his guilt?

Mr. Speer provided his own answers to these questions. And in doing so, he gave to others some understanding of what the "civilized" world regards as the aberration of Nazi Germany.

In an interview with The Washington Post in 1976, Mr. Speer said that history should remember him as "one of the closest collaborators of Hitler. What I said at Nuremberg, that I was responsible for everything that happened to me, will stick with me, rightly. It will be my stamp. I hope it will also be remembered that I was capable of three other things: to be an architect, manager and writer."

He added, however, that the last three things for which he hoped to be remembered carried a burden of their own: the guilt of the higher intellect. He expressed no regret over his guilty plea during the war crimes trials.

"Of course, one cannot reinstate the ambience or atmosphere of Nuremberg," he said. "But I am still convinced that the trials, for me, meant a world that was striving for a better future. It was a great step for future hope and in a subconscious way it is still active; both the East and West still refer to Nuremberg. It still has a high value in the minds of both Western and Communist nations and that will keep it alive."

Mr. Speer always maintained that, close as he was to Hitler, he never believed the Fuehrer's anti-Semitic rantings, never knew that the man actually undertook the extermination of European Jewry. In "Spandau: The Secret Diaries," he said he regarded Hitler's ravings as "a vulgar incidental, a hangover from his days in Vienna . . . a tactical device for whipping up the instincts of the masses." He also wrote that he came to realize that this was Hitler's fundamental conviction. "I shall never be able to get over having served in a leading position a regime whose true energies were devoted to an extermination program," he said.

On the question of Hitler's rise to power, Mr. Speer expressed the view that it came about as the result of the economic chaos that overtook Germany in the late 1920s and early 1930s. For himself, he said he was attracted by the Fuehrer's personal magnetism rather than his ideology. What is certain is that Hitler gave him commissions that were beyond the dreams of most young architects. Thus, Mr. Speer became one of the leading beneficiaries of the system he later was to denounce.

The British historian, H. R. Trevor-Roper, wrote that Mr. Speer was a moral neuter during the Nazi years. He also wrote that Mr. Speer embodied one of the most admirable of German characteristics -- an ability to work hard -- and an equally characteristic German failing -- an indifference to the purposes or consequences of the work at hand.

These characteristics were evident in Mr. Speer's performance as the head of the German economy from 1942 until the end of the war. Hitler, the unchallenged political head of the German state, began to turn over unlimited economic power to Mr. Speer when he realized that his offensives in the Soviet Union were failing and when the United States already had joined the war against him.

Until that time, the German economy never had been mobilized for war. There was no overall plan to allocate raw materials. Women had a negligible role in war work. In 1941, some 40 divisions of the army were returned to civilian life. Part of the reason was Hitler's conviction that the conflict already had been won. Another part was his reluctance to curb the self-interested activities of industrialists who had helped him to power.

Mr. Speer, who was only 37 and untrained in industrial management, changed all that. By the end of the war, he had control over every aspect of the economy, including labor. As the allied ring tightened, however, it became clear to him that peace must be made before the entire country -- and all that he had created -- was laid waste.

On March 18, 1945, he wrote to Hitler, saying that the war was lost and that "some material basis must be preserved on which the life of the people, however primitive, may be continued."

Hitler replied: "If the war is lost, the nation will inevitably perish. There is no need to consider the basis even of a primitive existence any more. On the contrary, it is better to destroy even that, and to destroy it ourselves. Besides, those who remain after the battle are of little value; for the good have fallen."

During his 20 years in Spandau, Mr. Speer made notes for his books on toilet paper and cigarette wrappers. They were smuggled out of the prison by friendly guards. The books made a fortune -- "Inside the Third Reich" sold more than 1 million copies in the United States alone.

Albert Speer was born in Mannheim, Germany, on March 19, 1905. His father and grandfather were architects before him. He was educated at various technical schools in Karlsruhe and Munich and at the Technical University of Berlin, where he received a degree in engineering. He was in private practice as an architect before attaching himself to Hitler.

A courtly, patrician figure, he never joined the Nazi Party and generally disdained the company of other leaders of the regime. In his interview with this newspaper, he said, "Maybe I was born to spend 20 years in prison. That is a slight exaggeration, but it is also true. Many people are astonished that I survived those years without bad effects on my health and one possible reason is that I didn't miss too much by being alone with my thoughts and with many books to study."

Of his diary, he said: "Diaries are usually the accomplishment of a lived life. This one stands in place of a life."

Mr. Speer, who lived in Heidelberg, is survived by his wife, the former Margarethe Weber, six children, and several grandchildren.