Woe unto the citizen who misses the April 15 deadline for filing federal income tax returns. Now it turns out that the Internal Revenue Service itself has missed a deadline, and the mistake may have cost the government a huge amount of money.

Last May 26, the U.S. Tax Court entered a judgment absolving American Telephone & Telegraph Co. from certain taxes the IRS claimed it owed. The IRS had until Aug. 24 to appeal the decision. The agency didn't file the appeal until Aug. 25, missing by a day a chance to take the issue to a higher court. The blunder could cost the government $100 million in disputed taxes and interest.The IRS, which hounds taxpayers when they fail to file on time, ought to take drastic action against its own officials who have acted so incompetently.