THERE WAS A TIME when I was a kid when it seemed that everyone in my family knew all there was to know about the stock market. They not only knew the basics, terms like "bull" and "bear" and even a mystery called "selling short," but they knew, too, when to buy and when to sell and, more important, what to buy and what to sell. At family gatherings you would get the impression that everyone sitting around you was a millionaire and it was only afterward that someone would cast doubt on the whole thing, saying something like. "If he's so smart, how come he lost his shirt on Amalgamated Properties?" I write this column knowing one of them will now say that about me.

I came to ruin on something called Commonwealth United Corporation. I am looking at the stock certificate now and a wonderful thing it is to behold. Three is a busty woman in the middle of the paper with a tiara on her head and a scroll in her hands. She is seated between two globes, one depicting the Eastern Hemisphere, the other of the Western, and to her right runs a little steam engine. There is a city of some size behind her with what looks like a proper steel mill. I suppose she is American Industry or Capitalism or maybe Virtue. Either way she is something of a fraud. She is not, as they say, worth the paper she is printed on.

I came to buy this stock on the advice of a cousin and I bought it as a cocky kid with the money I earned workingafter school and on the weekends at a place called Jack's Candy Store. I jerked sodas, made sandwiches, inserted the Sunday papers and stacked empty deposit bottles in the back room.

College and what you would have to call life wiped out my modest stock portfolio and I have to admit that I sold most of what I bought at less than what I bought it. Commonwealth United was almost a complete failure, plummeting in value to almost nothing where, in market jargon, it rallied and then, mercifully, faded from sight. It was a lesson to me that the market could go down as well as up, but that was the expert of the lesson. I thought no more of it, never considered that anyone had done me in, believed passionately as only a liberal could in American capitalism - and filed the worthless stock certificate in my desk where it has remained for years.

Then, about a month ago, The New York Times did a series of articles on Gulf and Western, the conglomerate. It was investigative reporting applied to the world of business and I was about half-way through the first piece, wondering, really, why I was reading it, when I came across a name I thought I knew - Commonwealth United. What followed was complicated, but suffice it to say that more was at work when it came to the value of this stock than simple forces of the market place. Things I should have known as a stockholder I was not told and when I put down the paper I had the distinct feeling that I'd been had.

I bring this up now because lately there has been a succession of stories that illustrate how little we pay attention to corporate American and what is being done there. It turns out, the Securities and Exchange Commision says, that New York banks were marketing New York City bonds even thought they knew he city was in bad trouble and not, to say the least, a good investment. It turns out also that workers at Dow Chemical making a substance called DBCP were not told that the substance had been linked to sterility.

I could go on. I could go on about how the Ford Motor Co. failed for four years to recall cars that posed a serious safety hazard and that have been linked to the death of one man and the injury of 11 others. Henry Ford called the failure a "regrettable" mistake, which it cerainly was, but he said nothing about how the company had simply taken it upon itself to decide that owners of the cars need not know that their cars might pose a safety hazard - however remote. You could cite also the whole Bert Lance affair and what we are learning about how some banks conduct their business with out money.

I know I've got a mixed bag here - apples and oranges, stock market losses, deaths and, worse yet in some ways, the sterility of men who might have been wanting a family. My loss is nothing compared to theirs. But there is a common thread here and it has to do with how corporations think they have the right to play it close to the vest - to tell the public nothing more than the bare minimum and to sometimes disguise even that.

You have to be reminded of that because corporations have been on the offensive lately, telling us in television commercials and full-page magazine ads how they are saving bird sanctuaries, bringing telephone service to peasant folk, and returning people to ancestral lands they've never seen. Unions inept as usual in getting their message across, have been taking it on the chin and Big Government is in retreat and so you have to be reminded that the reason unions can sometimes seem so unreasonable and the reason government has all those silly regulations is that they know who they are dealing with.

It's something I found out too late.