BERLIN — The head of Germany’s main Jewish organization has criticized writer Günter Grass for waiting decades to disclose that he had served during World War II in the Waffen-SS, the Nazis’ dreaded military force.

The president of the Central Council of Jews, Charlotte Knobloch, said yesterday that the admission negated Mr. Grass’s longtime criticisms of German politics and society for not adequately dealing with the Nazi past.

“His long years of silence over his own SS past reduce his earlier statements to absurdities,” Ms. Knobloch was quoted as saying by the Netzeitung online newspaper.

The author of the classic “The Tin Drum,” Mr. Grass has for decades stood as his country’s literary conscience, urging Germany to face up to its Nazi past and warning against any resurgence of imperial ambition. He has been widely criticized after acknowledging in an interview published Saturday in the Frankfurter Allgemeine Zeitung that he had served in the Waffen-SS.

Mr. Grass, 78, said he volunteered at age 15 for the submarine service and was refused, only to be called up for military service at 17. When he reported for duty in Dresden, he found it was with the 10th SS Panzer Division “Frundsberg.” He said that, under the sway of Nazi indoctrination, he did not view the Waffen-SS as something repulsive but as an elite force.

Mr. Grass has a memoir coming out on September 1. The book details his military experiences.

A Forsa poll for Stern magazine showed that 87% of those surveyed did not agree that Mr. Grass should give back his 1999 Nobel Prize for literature, as some critics have demanded. In the survey of 1,005 people taken Monday, 8% said yes, and 5% said they did not know.