I really have no idea. In 1942, Unknown magazine published a story by Henry Kuttner called "Design for Dreaming". That's the only earlier reference to the phrase I can find. It's barely possible that DfD was a transient catchphrase that was in the public consciousness at the time but that rarely showed up in ways visible to search engines. Otherwise, I gotta go with time paradox.
Update: There's a 1933 film called "Design for Living", which takes care of the cartoon's title. Depending on your tolerance for time paradox this might move into the realm of coincidence the fact that the cartoon parodies a short that doesn't exist yet. Or did the short take its cue from the cartoon?
Fri May 04 2007 21:49:
This is odd. Jaime Weinman embedded a 1954 (according to IMDB; internal copyright date is 1953) Warner Brothers cartoon called "Design for Leaving". The title makes it sound like a parody of the classic Populuxe short "Design for Dreaming", and that's exactly what it is. But "Design for Dreaming" didn't come out until 1956. Time paradox? Or something more sinister?
under a Creative Commons License.