When the Walt Disney television show went off the air last night after close to three decades, more was discarded than the familiar characters that so many millions of persons have come to love. Mickey Mouse, Donald Duck, and their friends, after all, will always be around - in reruns and specials, as well as in the Disney studio's new cable venture. But even more significant is the fact that with one or two exceptions, network television has now all but written off children's broadcasting and, to a large extent, the family hour. Given the enormous influence of television, such a trend should not be taken lightly.
A number of factors have come together to produce such a major shift in mass communications: demographics - the fact that the ''youth market'' is shrinking as there are fewer preschool-age children; the growth of independent stations, which now offer ''adult'' programs at all hours of the day and early evening that were once seen only late at night because of their subject matter; and, not to be overlooked, the fact that children today are more knowledgeable about the world than in years past - ironically, in great part because they watch many of the same television programs as their parents. And, as the networks point out, there are still a few ''action-adventure'' programs floating around the airwaves in the early-evening hours that are youth-oriented.
Still, television officials have a responsibility to ensure that younger children, who make up a sizable percentage of the TV audience and watch up to 30 hours of programming a week, not be ignored, as is now the case. There is not, for example, one daily program on network TV for preschoolers or young children. With the exception of an occasional special, there is not one daily network program for teen-age children. And anyone who has taken a look recently at Saturday morning TV fare - which garners substantial advertising revenue for network coffers - cannot but be saddened by it: hour after hour of cartoons, many of them filled with violence and may-hem.
Unfortunately, the Reagan administration has virtually abdicated its leadership role in this area. The chairman of the Federal Communications Commission, Mark Fowler, argues that ''market forces'' should determine children's programming. Fine in theory, except that children age 2, 3, or 4 do not have the economic clout of adults. If financial considerations alone are to determine the content of network television in the United States, then preschoolers and toddlers appear to be without any hope for quality broadcasting.
Yes, there is still public television, with programs like Sesame Street and the Electric Company. And Captain Kangaroo can be found in many areas on weekend network TV. But what about TV as an educator and communicator of values, ideas, aspirations, role models? The leaders of network TV - in pursuit of mass audiences and dollars - are turning their backs on America's children and, therefore, on the American family. Is it not time for them to remember that they have a public responsibility?