“Guns will make us powerful; butter will only make us fat.”
Radio broadcast (1936), as quoted in The New Language of Politics: An Anecdotal Dictionary of Catchwords, Slogans, and Political Usage (1968) by William L. Safire, p. 178
Variants:
Guns will make us strong, butter will only make us fat.
We have no butter... but I ask you, would you rather have butter or guns? Preparedness makes us powerful. Butter merely makes us fat.