A spate of recent health surveys paints a startling picture of American youths.

Apparently, not only are they lazy and sedentary, they don't know enough about nutrition to plan the simplest, healthy diet.But before the nation's adults work themselves into a lather about the condition of the rising generation, they need to look in a mirror. If today's kids don't know much about nutrition or exercise, it's because their elders haven't taught them. Good habits don't come naturally in a world filled with dozens of television channels and junk-food commercials. They must be taught, preferably by example.

Judging by the evidence, not a lot of teaching is going on.

This week the American Health Foundation, a private research organization based in New York, released a survey showing 48 percent of children in grades 2 through 6 believe apple juice contains more fat than whole milk. The truth is quite the opposite, by the way. More than a third also had the misperception that watermelon contained more fat than American cheese.

One quarter of the kids surveyed hadn't eaten any fruits or vegetables during the past 24 hours, and a similar number did not brush their teeth the night before.

Incredibly, 7 percent said they planned to start smoking cigarettes, while another 15 percent weren't sure.

More than half said they didn't wear a bicycle helmet. But that may not be such a problem, because other surveys show fewer and fewer youngsters ride bikes or do any other form of exercise. Roper Starch Worldwide, a public opinion polling firm, has documented a steady decline in the number of young people who participate in regular physical activity.

These survey results come at a time when scientists are finding stronger links than ever before between exercise, nutrition and health. By some estimates, one-third of all cancer cases in the United States could have been prevented by a better diet. People who exercise regularly and avoid smoking live longer, more productive lives than those who do the opposite.

Ironically, another national survey was released last week by the Centers for Disease Control and Prevention. It showed that nearly 87 percent of American adults consider themselves to be in good to excellent health. When surveyed, most of the respondents reported few if any physical or emotional problems during the previous 30 days.

That's great news. But unless all those healthy grown-ups pass along their wisdom, the rising generation may learn too late that steady diets of American cheese and whole milk, consumed while smoking cigarettes in front of a television set, will not lead to a long and productive life.