Origins: From January 14 to 24, 1943, Franklin D. Roosevelt and Winston Churchill held a wartime conference in French Morocco, near the site of the Allied landings in North Africa two months earlier. The meeting was not announced to the American public until it had concluded, and it came to be known as the "Casablance Conference" because it took place near the city of Casablanca (recently popularized by the movie). One of the more unusual wartime rumors which sprang up later was that agents in nearby Spanish Morocco had found out about the plans for the secret Casablanca meeting in advance and passed this information along to the Germans, but the Germans did nothing with this bit of intelligence because — since "Casablanca" literally means "white house" in Spanish — they mistakenly assumed the conference was being held at the White House in Washington, D.C., where they could do nothing about it. Had the Germans known Roosevelt and Churchill were coming to North Africa instead, rumor had it, they certainly would have tried to kill one or both of them. (The rumor's likelihood was bolstered by the fact that German planes had bombed Casablanca only two weeks before the meeting.)
Differences in orthography make this legend unlikely as a true story, as the name "Casablanca" and the term "casa blanca" are distinguished by the case of their initial letters and the separation of the latter into two words, differences which should have been obvious to any translator. In any case, the Germans did know about the conference from the beginning (which was actually held in Fedala, sixteen miles north of Casablanca) and announced their knowledge to the rest of the world (although wartime censorship prevented Americans from finding out about the meeting until after it was over). Most likely this tale was just one of several rumors based on the coincidence of "Casablanca" having a dual meaning in Spanish, such as this one connected with the famous Warner Bros. film:
The movie magazines and movie columnists were commenting frequently on the film and rumors of various kinds began to circulate. Warner Bros. made no effort to stop them. One such rumor was that the movie was a parody on the relationship between President Franklin D. Roosevelt and Prime Minister Winston Churchill. Rick was Roosevelt, who lived in a white house (casa blanca), and Laszlo was Churchill, a clever and sophisticated European who was trying to draw Roosevelt into the fray
Osborne, Richard E. The Casablanca Companion. Indianapolis: Riebel-Roque, 1997. IBSN 0-9628324-3-X (pp. 219-220, 224).