DESPITE THE opposition of numerous health and religious organizations, the Reagan administration has issued a regulation that will require clinics to notify parents when their teen-age daughters are given birth control devices. The legality of the regulation will be tested in the courts, but the important issues involved are essentially social rather than legal.

Families certainly have a legitimate interest in all matters--including sexual activity--that may affect the well-being of their teen-age children. That interest, however, is generally balanced against any competing interest of society or of the child. In the case of teen-agers who contract venereal disease, for example, the new regulations come out on the side of continuing privacy for the young patient. That is because it was decided--wisely--that the public's strong interest in encouraging people to seek prompt treatment for venereal disease justifies prescribing antibiotics to a minor without parental approval.

Up until now, the public health interest has supported the protection of privacy for teen-age girls seeking birth control help from federally funded clinics--boys, of course, are not affected, since male contraceptives can be purchased in drugstores. Yes, there are small risks involved in taking birth control pills--the almost universal choice of teen-agers-- but they are much smaller than the well-documented risks--to mothers, babies and, ultimately, the society--of child-bearing by teen-age mothers. In fact, medical complications are more likely to come from taking penicillin for venereal diseases than from taking modern birth control pills.

Congress thought about these choices when it amended federal law in 1978 to make teen-agers a specific "target" population for family planning programs. When Congress reauthorized the program in 1981, it recognized the desirability of involving parents where possible by including language that "encouraged" parental involvement. Most clinics do this already. But encouraging and requiring are very different things.

Many parents want to know about their daughters' sexual activities. And many daughters--over half who now come to birth control clinics--will volunteer the information. But fear of being found out will doubtless prevent many young women from availing themslves of contraceptives, though it will not prevent their sexual activity. To imagine that discouraging birth control help will discourage teen- age pregnancy is to ignore human history.

In fact, contrary to popular perception, the rate of births to teen-agers is less than 60 percent of what it was 25 years ago. What has changed is that many fewer of those births are sanctified by marriage before they occur. That's a major social problem. It will, however, be exacerbated rather than solved by the administration's new regulation.