You missed something during David Letterman's interview with Brett Butler Nov. 7, but don't blame yourself. At one point, the Grace Under Fire star said of Walt Disney: ''His last words were, 'Whatever you do, don't let the Jews get the place.' And then they went and bought it.'' The joke was bleeped from the broadcast. Almost as surprising as the inappropriate quip was the decision to censor it. Usually, only expletives are purged. A Letterman spokeswoman will say only that the show and CBS make censoring decisions together. Says Butler, whose sitcom airs on Disney-owned ABC: ''I said 10 [controversial] things, and I couldn't believe they cut that one. I said stuff about dykes. They cut the one that was the most true.'' While she doesn't regret her wisecrack, Butler, currently in drug rehab, says she has a joke ready in case anyone asks: ''I'd be tempted to say I was so high I don't remember the spot.''