ONLY A dyed-in-the-wool fuddy-duddy would not have been pleased as punch at the exoneration of Dr. Mudd, yet even with a light at the end of the tunnel, a little rain must fall. Until this week Dr. Samuel Mudd had occupied a dark spot in American history as the man accused of being an accomplice of John Wilkes Booth, whose broken leg he set on that infamous night. But now President Carter has given the doctor a leg up by declaring him officially innocent, so his name is no longer mud. But that is exactly the problem.

For while the Mudd family of Saginaw, Michigan, has been tramping down the historical vineyards for six generations, working for the clearing of their surname, the rest of the country has happily adopted that name into the language, in the perfectly apt and picturesque expression: "His name is mud." Naturally, the joy in using that expression was predicated on the assumption that the good doctor was not so good. Now that he's officially innocent, however, a person's bad name may be many things from this time forward, but in no eye will it be mud.

But what if this linguistic revisionism begins to touch some other of the famous names that have added so much to our talk? George, for instance. It would be a disappointment of national proportions if George turned out to be a fellow known for shucking responsibilities; or if Johnny-come-lately were discovered to have been Johnny-on-the-spot; or if Kilroy was nowhere. What would life preservers be called if Mae West were revealed to be less buoyant than appeared; or if the Joneses - whoever they were - turned out to be Amish? What of Simon Legree, if the evil attributed to his John Hancock is not the real McCoy?

As for this Mudd affair, it has made matters worse than they appear. For in the very week that Dr. Mudd has been cleared, President Lincoln was found to have cheated on his expense accounts. It would be hard enough to have to say "His name is Abe." But "Honest Mudd"?