MemeMachineGo!

Goebbels is quoted as saying:

If you tell a lie big enough and keep repeating it, people will eventually come to believe it. The lie can be maintained only for such time as the State can shield the people from the political, economic and/or military consequences of the lie. It thus becomes vitally important for the State to use all of its powers to repress dissent, for the truth is the mortal enemy of the lie, and thus by extension, the truth is the greatest enemy of the State.

Someone is even selling that quote all over various Cafepress merchandise.

But it seems to be yet another apocryphal quote.

Rather than championing the use of the big lie as a propaganda technique, both Goebbels and Hitler criticized its perceived use by others, Hitler in Mein Kampf attributing its use to Jews:

In this they proceeded on the sound principle that the magnitude of a lie always contains a certain factor of credibility, since the great masses of the people in the very bottom of their hearts tend to be corrupted rather than consciously and purposely evil, and that, therefore, in view of the primitive simplicity of their minds they more easily fall a victim to a big lie than to a little one, since they themselves lie in little things, but would be ashamed of lies that were too big. Such a falsehood will never enter their heads and they will not be able to believe in the possibility of such monstrous effrontery and infamous misrepresentation in others; yes, even when enlightened on the subject, they will long doubt and waver, and continue to accept at least one of these causes as true. Therefore, something of even the most insolent lie will always remain and stick-a fact which all the great lie-virtuosi and lying-clubs in this world know only too well and also make the most treacherous use of.

and Gobbels to the English:

One should not as a rule reveal one’s secrets, since one does not know if and when one may need them again. The essential English leadership secret does not depend on particular intelligence. Rather, it depends on a remarkably stupid thick-headedness. The English follow the principle that when one lies, one should lie big, and stick to it. They keep up their lies, even at the risk of looking ridiculous.