"I have personally experienced the reality of the 'ideologies of evil'. It remains indelibly fixed in my memory," he says in the book, which is a series of conversations he had in Polish with fellow philosophers in the summer of 1993.

Excerpts of the book, which was announced Wednesday at the Frankfurt Book Fair, were made available by the Italian publisher Rizzoli.

The pope, who has been credited with helping bring about the fall of Communism after his shock election in 1978, reveals that even an optimist like him had moments of pessimism during his life under Communist oppression.

"To me it was quite clear that Communism would last much longer than Nazism had done. For how long? It was hard to predict," he writes.

"There was a sense that this evil was in some way necessary for the world and for mankind. It can happen, in fact, that in certain particular human situations, evil is revealed as somehow useful inasmuch as it creates opportunities for good."

Many historians believe it was his support for Poland's free trade union Solidarity after he became pope in 1978 that helped the union go on to form the East Bloc's first free government.

NAZI "BESTIALITY"

The pope, whom Jews have credited with improving Catholic relations with them more than any pontiff in history, also reflects on Nazism, which he calls a "bestiality."

"The Lord God allowed Nazism 12 years of existence ... evidently this was the limit imposed by Divine Providence upon that sort of folly," he says.

"The full extent of the evil that was raging through Europe was not seen by everyone, not even by those of us who were living at the epicenter. We were totally swallowed up in a great eruption of evil," he says.

"Both the Nazis during the war and, later, the Communists in Eastern Europe, tried to hide what they were doing from public opinion. For a long time, the West did not want to believe in the extermination of the Jews," he writes.