BACK in May I wrote a column about the problems of the American family. It focused on the critical role of parents in rearing children in a society where drugs and violence are rampant, and where many of those who produce our movies, our books, our modern music, and our television programs seem intent on pushing to the limits our tolerance of the obscene and the decadent.It must have touched a chord. The response was surprising as people in government, parents, grandparents, and others wrote to echo their concerns about the state of society, and specifically the abdication of parental guidance. One respondent, writing about the "evils in the current era (drugs, teenage-pregnancy, school dropout, violence)," said: "The cause is the disintegration of the traditional family. There is nobody bringing up the kids." Clearly, readers are concerned, and with good reason. For now comes the National Commission on Children with some alarming facts about the changing American family. Headed by Sen. John D. Rockefeller IV (D) of West Virginia, the commission has recommended some sweeping changes designed to strengthen the family and improve the lot of children. One is a $1,000 income tax credit for each child in America. Low-income families owing no income tax would get an equivalent cash payment. Political sophisticates in Washington are sniggering at the idea, calling it unrealistic in a time of recession. With increases in government spending for health care and other needs of children, all this would cost the government between $52 billion and $56 billion in the first year. But if it is difficult to see where the money is coming from, we should pay attention to the problems of children that the commission has underlined, and to the disturbing trend lines it has developed: * More than half of all 15- to 19-year-olds are sexually active. Each year more than a million teenage girls become pregnant. * Though the number of adolescents in our society is declining, rates of adolescent crime and violence are rising. Almost two million adolescents were arrested last year. Teenage boys are now more likely to die from gunshot wounds than all "natural" causes combined. * In a 1990 survey, nearly half of all teenagers reported having used illegal drugs. While alcohol use has declined among youths, 57 percent still report recent drinking. * Fewer than half the 17-year-olds in school possess the skills and basic knowledge required for college and many entry-level jobs. There is no question but that a lot of this is attributable to the collapse of the traditional American family, and the lack of parental guidance and discipline. More than 16 million children in America - one out of four - now live with only one parent, usually a mother. Almost 60 percent of mothers with children under six years old are in the work force. Almost 75 percent of mothers with children between six and seventeen years old are in the labor force. As more parents work outside the home, more children are cared for by people other than their parents. Nearly 20 million children under fifteen are cared for by an adult other than a parent for some period of time each day or each week. Some 1.3 million children between five and 14 care for themselves during the hours they are not in school. The Rockefeller commission calls for a new commitment to "forming and supporting strong, stable families as the best environment for raising children." What about the argument that families need two incomes to get by these days? Say these particular letter-writers: "Couples newly married demand amenities which we have been able to attain only late in our lifetimes ... the problem is the demand for instant gratification - the rewards of a lifetime at the start of it." Though the reasons for stress upon the family obviously vary, there is no question that the changing form of the American family has exacerbated the problems of America's children.