IT IS NOW 10 years since Sheila and Katherine Lyon disappeared. The girls, then 12 and 10, were last seen at the Wheaton Plaza Shopping Center on the day before Easter 1975. For many months people in this community watched intently for the children, relayed tips and information to the police and prayed for their parents, John and Mary Lyon. But Sheila and Katherine have not been found. Though their disappearance seemed at the time to be unique and horrifying, we know now that this kind of tragedy is widespread.

The National Center for Missing and Exploited Children, established by Congress in 1984 to be a clearinghouse for information on youngsters who have disappeared, estimates that 1.5 million children are reported missing each year. Two-thirds are runaways, and a large number of the others have been unlawfully taken by a parent to whom the courts have refused to award custody. The remainder, like the Lyon sisters, have apparently been abducted by strangers and are the most difficult to locate.

Public response to the search for missing children has been impressive. Photographs of children have been displayed on milk cartons, shopping bags, trucks, toll booths and even by members of Congress appearing on cable newscasts. Recently, the National Center, in cooperation with the private National Child Safety Council and the American Gas Association, announced a campaign to involve utilities in this work. Each month, photos of two children will be enclosed with gas bills mailed out in 42 states. The same children will be featured in every area of the country, and the pictures will be sent directly to 30 million households. Other utilities will be asked to make a similar effort. Only those children thought to have been abducted by strangers will be sought through this program.

Whether you are celebrating Passover, Easter or just the beautiful spring weather this weekend, the joys of family gatherings are multiplied when children are part of the celebration. The importance of efforts by public and private organizations and individuals to find missing youngsters is apparent to anyone who has ever loved a child. That work is now organized, imaginative and effective. It deserves broad support.