If you haven't spotted someone smoking marijuana in public by now, you've probably been out of the country . . . for years.

Smoking dope in the great urban out-of-doors is right commonplace. Even so, those of us past the age of consent still remember when it was done in private between consenting adults and jazz musicians. Going public is something that evolved in the past several years, a joint here and a joint there, until suddenly we were in the age of the roll-your-own, no-name cigarette anywhere you choose.

I came along during the genesis of the new marijuana acceptability. Mine was the college crowd just before the full-tilt marijuana generation. Our way of getting loose was alcohol, all you could chug and still stay on your feet.

Marijuana was around. You'd see its packets changing hands for money in the semi-darkness of campus bars. But the hands belonged to that breed recalled today is hippies, almost always white, rumpled and under the influence of a rainbow of pills lending them that glassy-eyed nonchalance. They were sparce on campus.

Now the hands are as likely to be black as white, and as likely to belong to our children's teachers as to our children. Marijuana, the drug of the laid-back, has invaded a generation and is threatening to deal a cool, crushing blow to its future.

It's not the only drug out there, but it's the most accessible and sold in the right price range. It's so common we tend to forget how little we know about its long-range effects. And what we do know doesn't seem to be registering.

Read any of the business reports on liquor companies and you realize how hard liquor has fallen from grace. Young people now use booze as a chaser for their marijuana.

It is becoming a part of the culture, so widespread that just about anyone, anywhere, in their 30s and younger, regardless of profession and social standing, has probably had at least one toke. A growing number are everyday users.

Which is, of course, why proponents of the D.C. Marijuana Initiative thought they had a good chance of getting their issue on the November ballot (it died of too few petition signatures last week), and Lafayette Park was the setting for a 13th annual smoke-in July 4th. Youngsters, 9, 10, 11, pass joints among one another on the streets. Just like adults.

It's done in parks, at ball games and popular music concerts, so much so, that it's the rare cop who doesn't look the other way. "Someone smoking dope would almost have to get in my way for me to arrest him," a narcotics cop told me several years ago. It's small potatoes, he said.

But it isn't for people trying to build a strong community. In its March issue, Psychology Today looked at the effects of marijuana on human function, and found that its use impairs concentration and memory, to the surprise of no one who indulges and routinely forgets where he was heading with the sentence he began seconds before.

And we're taking it to work. A labor union official on a recent Bill Moyers television program said one of the biggest problems facing his union stems from complaints about workers ducking out to the restroom for a quick smoke. You figure out how that's affecting the quality of work.

By now, the findings of health studies have debunked the long-held notion that the weed is harmless.

But all the harm is obviously not physical. Smokers know marijuana breeds complacency, laziness. If you smoke, you're left with little incentive for anything else, except the doper's favorite passtime, cooling out.

Some people can afford to. Life is just sitting back waiting for them to give it a spin, but if you're black in D.C. today, that's not a posture you want to be in.