THE SAGA of David Alan Etheridge, in a Virginia prison since 1972, was recapitulated the other day in this newspaper, and it continues to make appalling reading. Mr. Etheridge was sentenced in 1972 by a Norfolk jury to 120 years in prison for selling one ounce of marijuana. At the time of his trial, the attitude toward drugs in this country was different from what it is today. As the arresting officer himself was quoted by Caryle Murphy of The Post, "Being tried for drugs (in 1972) was like being tried for drugs (in 1972) was like being tried as a Communist in the '50s". That is not a bad analogy. It illustrates and how, with additional information, the climate can change. Today, the nation's top drug treatment official, Dr. Robert duPont, states flatly, "Decriminalization of marijuana possession makes sense on economic and humanitarian grounds." No federal official could have said that in 1972 and hoped to keep his job.

But this transformation to a more tolerant attitude (and a few President who favors decriminalization) leaves the David Etheridges just where they were in 1972 - in prison. In Virginia alone, there are 160 persons in state prisons for marijuana offenses - this, at a time when the state prisons of the nation are the most crowded they have ever been, by the recent count of Corrections Magazine. In all, a record 275,000 persons are now in the nation's prisons; mixed in among the murderers and the armed robbers are perhaps as many as 4,000 persons whose crimes were that they were involved in some sort of marijuana transaction - some of them having been found to be active pushers, but many having been found in "possession" of the stuff simply as users.

On humanitarian grounds - and in logic - that kind of incarceration makes little sense. In 1972, this country was perplexed by an ever-growing drug problem that nobody seemed frightening. We heard warnings in those days that we were turning into a "nation of zombies," that we were awash in permissiveness and dangerous self-indulgence.

Now, after nearly $20 million in research on marijuana alone, we know a lot more about it and about the extent that it both related to, and quite distinct from, so-called hard drugs. We know that the use of hard drugs of all kinds presents society with a much different and far greater danger of deterioration than does the "killer weed." So young Mr. Etheridge, now 27, lives out the best years of his life in jail for selling something that 15 million Americans are estimated to use on a regular basis and that 30 million or more have tried at least once. He will be first eligible for parole in 1982, his 120-year sentence having been reduced by ajudge to 40 years. The officer who arrested him said, "I was sorry to see him get such a large sentence. He wasn't a large trafficker, he was a go-between and an addict. A victim of circumstance." Mr. Etheridge, sitting in prison, is experiencing the single most serious consequence yet to be associated with marijuana.