Both books are prohibited in Germany and are not sold by the German affiliate of Amazon.com. However, a German customer can easily circumvent the law by ordering directly from U.S.-based sites and having the books sent to his home address.

Amazon.com followed up its confirmation of orders for Hitler's book and "Protocols" by suggesting additional reading, including "White Power" by George Lincoln Rockwell, the late leader of the American Nazi Party.

Rabbi Abraham Cooper, associate dean of the Wiesenthal Center, initiated the complaint through letters to German Justice Minister Herta Daubler-Gmelin and to the CEOs of Amazon.com and of Bertelsmann, the German media conglomerate that owns 50 percent of Barnesandnoble.com.

Bertelsmann recently appointed an international commission to investigate the company's activities during the Nazi era.

The initial reaction of the two online booksellers was to reaffirm their policies of selling any book in print to any customer, the New York Times reported Monday.

However, a news report from Berlin quoted Bertelsmann spokesman Markus Payer as saying his company was taking the matter very seriously.

"There is a conflict between the freedom of expression on the one hand and our duty to protect society from these totalitarian influences," Payer said.

When a merchant ships a product, he is obligated to uphold the laws of the jurisdiction to which it is being sent, Jack Goldsmith of the University of Chicago Law School told the New York Times.

Cooper, however, said booksellers must look beyond whether something is simply legal.

"Just because something is technologically possible, it doesn't mean it's the right thing to do," he said.

"We also have a generational gap here. The online search engines are being developed by Generation X people and even younger ones. I wonder if they pay any attention to their social responsibilities."