WHILE THE DEBATE over legalization or decriminalization of marijuana rages on, the National Institute on Drug Abuse has recently published two important documents that should change the focus of most people's attention. One is a summary of current research findings on the effects of marijuana on health, and the other is a survey of the extent and intensity of current marijuana use.

The survey shows a continuing trend of more frequent use, by younger individuals, of more potent marijuana. The fraction of 12- to 17-year-olds who have ever used pot has grown from 7 percent in 1967 to 14 percent in 1971 to 31 percent last year. Of this age group, 17 percent are current users -- defined as those who have used the drug within the past month. In the past five years, daily use by high school seniors has almost doubled, and now stands at 10.3 percent. Almost 40 percent of this year's graduating class are current users.

These are underestimates, since they are based only on interviews of those actually attending school. Nor do they reflect the increasing potency of the plant. The fraction of THC -- marijuana's principal psychoactive component -- in plants imported from Mexico has increased twentyfold since 1973. And marijuana from Columbia, which accounts for more and more of today's supply, is estimated to be twice as potent as the current Mexican crop.

The biological effects of marijuana use are much less certain, since most experiments must be done on animals. But some effects are becoming clear. Marijuana produces lung damage as great as or greater than that caused by tobacco. It also contains more cancer-producing substances than does tobacco smoke. The Drug Institute concludes that "it appears likely that daily use of marijuana may lead to lung damage even greater than that resulting from heavy cigarette smoking." Research on animals, as yet unconfirmed in humans, shows a definite suppression of the immune system -- the body's chief defense against illness. A range of evidence indicates that marijuana affects the delicate balance of glands and hormones that govern sexual development and reproductive function, including effects on fertility in both sexes and damage in the developing fetus.

The most serious effect appear to be psychological -- especially in young people. Any biological system is more vulnerable to damage during periods of rapid change than during periods of stability, and 12- to 17-year-olds are in a period of extremely rapid psychological change involving intellectual skills and learning, emotional growth and personality development. There is a growing consensus that each of these functions may be seriously impaired by marijuana use during this period.

While this may seem a pretty sobering list, the sum of what is still unknown is even more scary. Marijuana has only been widely used in this country for just over 15 years. Most cancer latencies are 20 years or longer and, as has been demonstrated in the case of alcohol and tobacco, it may requre decades of use by very large numbers of people before even devastating effects of a drug become evident.

Pot is clearly a dangerous substance -- at least for 12- to 17-year-olds and possibly for older people as well -- and its illegal status has obviously not curbed its availability. While the appropriate legal treatment of marijuana possession and sale is one important issue, there is also an urgent need to find ways to diminish marijuana use by those who are being hurt worst by it.