JUST ABOUT everyone agrees there ought to be a greater national effort to collect child support payments from absent fathers. The Children's Defense Fund says such an effort should be made particularly in behalf of teen-age mothers. That makes little sense to some people, including officials who are finding it tough enough to force adults to pay. Why spend valuable time and resources to track down teen-agers likely to have neither jobs nor funds? they ask. But there is a case to be made for what the CDF recommends.

Too many young males who father children feel their behavior has no consequences. The society ought to insist on the principle of responsibility because it's right; to do otherwise is to give in. And the program may have a deterrent effect as well. The young men would be obliged to undergo paternity tests; their income at the time or in the future would have to be shared to help raise a child certified as theirs. They would be put on notice.

As recently as 1974, more than half of the adult fathers in the country were married and living with their spouses by the age of 22. By 1985, only one of every four fathers was married and living with his wife at that age. That's a trend the society cannot afford not to attack. The CDF points out, by the way, that child support officials often wrongly suppose that all the fathers in cases where teen-age girls bear children are teen-agers also. In fact, almost half of them are 21 or 22 years old.

The current child support system -- for mothers of all ages -- hasn't worked. In 1985, for example, the state of Wisconsin collected child support for just 42 percent of the mothers who were entitled to it, and that was the best any state could do that year. Sen. Daniel Patrick Moynihan has proposed welfare legislation to beef up child support enforcement with automatic payroll deductions by employers and provisions to establish paternity as a first step. Some of the same provisions were included in the welfare bill just passed by the House. And the CDF is right to suggest that mothers who are still teen-agers may need the most help of all.