The 78-year-old Grass told the daily Frankfurter Allgemeine Zeitung that the stunning confession would feature in his memoir "Peeling Onions," which is due to appear in September. So far, it had only been known that the author, best known abroad for his 1959 novel "The Tin Drum," was conscripted into the German air defense forces.

But in his autobiography he also recounted that he tried to join the Third Reich's submarine forces when he was 15 years old but was rejected because he was too young. He said that he was drafted into the elite Waffen SS the following year but denied suggestions that he joined willingly.

Grass, for many years a prominent leftist and pacifist, was wounded in 1945 and sent to an American prisoner of war camp.

"I wanted to make clear once again what happened then and above all things concerning me," he told the newspaper. "My silence for all these years is one of the reasons why I wrote this book. It had to come out."

Contemporaries disappointed

Fellow German author Walter Kempowski was among the first of his Grass's contemporaries to comment, telling the Berlin daily Der Tagesspiegel that the revelation was "a bit late" while Grass biographer Michael Jürgs said he was "personally disappointed" and lamented "the end of a moral authority."

Leading literature critic Hellmuth Karasek criticized the timing but also agreed there was no reason to reproach Grass as he had done much in his career and life since the war to inspire people.

"The fact he was in the SS at 17 is by itself a misdemeanor -- had Grass not been one to throw his weight around as a moral authority so much since then," Karasek told German radio. "If I were cynical, I would say he did not reveal it sooner at the risk of not winning a Nobel prize. Don't misunderstand me: Grass deserved the Nobel prize more than any other German writer. But everything now has to be seen in a new light."

Joachim Fest, a leading historian, told Der Spiegel magazine: "After 60 years, this confession comes a bit too late. I can't understand how someone who for decades set himself up as a moral authority, a rather smug one, could pull this off."

Michael Wolffsohn, a prominent military historian, also faulted Grass for waiting so long. Grass's "moralizing, though not his storytelling, life's work is devalued by his persistent silence," Wolffsohn wrote in the online Netzeitung daily.

CDU politician demands return of prize

Meanwhile, Wolfgang Börnsen, the parliamentary spokesman on cultural affairs for the conservative Christian Democratic Union called for Grass to return the Nobel Prize he won for Literature in 1999. Börnsen told the German daily Bild that Grass should adhere to his own moral standards and "honorably return the prize."

Sections of the German press were equally deflated by the admission.

"Grass's confession right before the publication of his autobiography leaves behind a bad taste of book promotion," wrote Bild am Sonntag newspaper columnist Helmut Böger. "Even after his admission, Grass remains Germany's most important living author. But he has lost his standing as a moral authority. He cannot be castigated for being a member of the SS... But he can be for lying about it for 60 years."

However, Ralph Giordano, a leading German-Jewish writer, said he would not condemn Grass and praised his belated confession.

"It's good what Günter Grass has now done," Giordano said. "What's worse than making a mistake is not coming to terms with it. His example also shows how seducible young people can be."

The muted reactions outside of Germany were mostly of displeasure and disappointment.

Robert Fulford, a columnist with Canada's National Post, accused Grass of hypocrisy.

"During his long career as a public man, Grass has never passed up a chance to speak out for outspokenness," he wrote. "'The job of a citizen is to keep his mouth open,' he liked to say -- though not necessarily in all cases, of course."

Walesa calls for renouncement of citizenship

Former Polish President Lech Walesa took an even harder line by demanding that Grass renounce his honorary citizenship of Gdansk. Grass, who was born in the Baltic port of Danzig, now the Polish city of Gdansk, became an honorary citizen of the city in 1993.

"An uncomfortable situation has developed," Walesa, who is also an honorary citizen of Gdansk, said in an interview Monday with the Bild newspaper. "I do not feel comfortable in that company. I do not know whether one should consider revoking the title. If it had been known he was in the SS, he would never have received the honor. It would be best if he relinquished it himself."

In his admission, Grass said he never fired a shot during his time with the feared elite force whose notoriety he only grasped once his unit had been defeated, when one of his superiors ordered him to get rid of his uniform.

Nuremberg trials revealed truth

The feared paramilitary unit was branded a criminal organization at the Nuremberg war crimes trials. Only then, Grass claimed, did he start to understand.

"I was stupid enough to believe that Germans would not do such things and took it all for propaganda," he said. The revelations of SS brutality at Nuremberg trials then caused him "feelings of guilt and shame."

Grass has spent the decades since the end of the war demanding that Germans come to terms with their Nazi past by coming clean on it.