STUTTGART, Germany — The swastika is illegal here, as is the Hitler salute. Germans have learned after decades of fighting their expression that the ideas behind them cannot be outlawed.

But the question facing German officials today is whether pushing those ideas underground makes them more radical in the short term, and maybe even more attractive in the long run, precisely because they are forbidden.

In the debate over the rise of the far right in Europe, Germany has remained, for obvious reasons related to its history, very much the exception. The kind of mainstream far-right parties so common in the rest of Europe are nowhere to be found here.

But the anti-Islam and anti-immigrant ideas that have taken root across the Continent burst into the mainstream debate here last year when a book by an executive with Germany’s central bank, Thilo Sarrazin, blaming Muslims for “dumbing down” Germany sold more than a million copies. The national discussion culminated with Chancellor Angela Merkel’s declaration at a party conference last October that multiculturalism had “utterly failed.”

That same month a study by the Friedrich Ebert Foundation, an organization affiliated with the left-wing Social Democratic Party, found that nearly a third of Germans believed that foreigners were here to take advantage of the welfare state, and that close to 60 percent of those surveyed favored restrictions on the practice of Islam....'