Sheilia and Katherine Lyon, then 12 and 10, disappeared from the Wheaton Plaza Shopping Center the day before Easter, 1975. Each spring the anniversary of this unresolved tragedy is noted. Many citizens who did not know them reach out to John and Mary Lyon, the parents who suffered this agonizing loss.

But children disappear all the time across America. Thousands run away from home. Others are "snatched" by a parent who has not been awarded custody in a divorce proceeding. Many simply disappear, presumably kidnapped, often abused and frequently murdered. Police are sympathetic in such cases, but often the children have been taken out of the area, perhaps to another state.

It is to help in such circumstances that a proposal is circulating for the federal government to maintain a national information bank on missing children and a file of unidentified deceased persons, of which there are 1,000 a year, many of them children. Families whose children have been missing for long periods would surely prefer the finality of bad news to the anxiety of an unexplained disappearance, if that is the choice.

Sen. Paula Hawkins (R-Fla.) is the author of a Senate bill, which has 70 cosponsors, to set up these data banks; Rep. Paul Simon (D-Ill.) has led this effort in the House. The FBI estimates it would cost only $47,000 to establish the two information files and $285,000 a year to maintain and use them.

The widespread support and unobjectionable logic behind this proposal make one wonder why such legislation was not enacted long ago. One reason, Justice Department attorneys suggest, is that some distressed parents will think that the FBI has a responsibility to take over the search for a missing child. But the FBI will not conduct the search; it will only keep the data. The bureau itself objects to a provision that allows citizens to file information on their own, instead of working through local police, but the bill's sponsors believe that problem, if it is one, can be eased.

Sen. Hawkins estimates that existing FBI files hold informatio on only 10 percent of all missing children. Runaways are not in those files. There is no central clearinghouse of information on unidentified bodies. Setting up these systems may involve technical problems and a bit more work for federal law enforcement officials. But the costs are far outweighed by the benefits of reuniting some parents with their missing children and of ending, however painfully, the distress of other parents who wonder whether their children are alive.