ALMOST EVERY WEEKEND for the last couple of months. I have sat at the typewriter at home, trying to write an article that I have been unable to write. Much of it is easy - a review of a book about the origins of most American Jews. The rest of it, though, is very hard to write. It has to do with whom I am, where I came from and finally why I care so much about all this.

The last part of that is what troubles me. Why should I care that I can't trace my ancestry back more than two generations - that it plunges into the darkness of the Eastern European ghetto sometimes around the turn of the century? Why should I envy people like my wife who know they are descended from Great Lakes ship captains and people who came from England and Ireland?

I bring this up now because of "Roots" which has been running on television and because persons in my office are talking about it. Some of these persons are black and it is clear that "Roots" has affected them profoundly. They would like to know something of their own roots, like to know what Alex Haley has found out - where they came from and who their ancestors were. I ask them why they care because I am interested in finding out why I care. They say they are interested and leave it at that. Only that is no answer at all.

Maybe it's the times, maybe the Bicentennial had something to do with it, but it seems to me that lots of people are searching for their roots. Everytime I've done a column in which I mentioned my family, helpful people have called to tell me that I could go to the National Archieves to find the manifest of the immigrant ships. They say it would be a start. For me, it would also be the end of the road.

I have two friends who are researching their own roots. They spend evenings with aging relatives, tape recording recollections and praying that the relative will live for yet another session. I met a man at a party who told me that he was saving to go to Russia. He has it all figured out. He will go to where the archives of the army are kept and he will look for an ancestor who supposedly fought with the star against Napoleon. It will cost him a bundle, but he doesn't seem to care. The past for him is more important than the future.

I have made a pass at this sort of thing myself. My grandparents are gone now, so I have sat with my mother, a map on my lap, and I have asked her to recall her childhood in Europe - whether it was half a day by horse and cart to Warsaw or a day. These things are important. Half a day means that the town on the map where my finger rests is the place where she was born. I try to imagine it, but all I see is the set from "Fiddler on the Roof."

But it is useless. You can find the town and listen to some of the stories, but the generation before my grandparent's is lost forever - obliterated in a succession of programs and flights and, finally, the holocaust of World War II. There is a family story that my mother's grandfather was a giant of a man and that the English equivalant of his name would be something like "Big Harry." I don't believe the story, but I see the man nonetheless. He towers above everyone else, a tall man with a long beard - proud, regal, devout. There is another story about an ancestor who was supposed to be a horse thief. I don't believe that one either, but it appeals to me anyway - adds a dash of romance, I think.

But my problems are nothing compared to those of blacks. My ancestors took their names, their customs and their religion with them on the boat, and if some of them plunged into the melting pot and drowned, changing their names, for instance, then they did it out of choice. Blacks had no choice. They lost their names, their religions, their customs and their freedom - their sense of identity as a people. It is cruel to rob a people of their past.

But the question remains why it all matters - why it is not enough to be just what we are.I think some of it has to do with the geographical rootlessness of American society and I think some of it has to do with another kind of rootlessness - how you can be in one business one year and another the next year and lose, in the process, the ability to define yourself by what you do. Some of it has to do with having children and what that does to you - how it makes you think of your father and his father and all the fathers that went before. Suddenly, you are part of a process.

But I think, too, that we tend to pay more attention to our ancestors the older we get and the more we appreciate our own limitations. I don't know when you stop thinking that you'll be President of the United States or Babe Ruth or whatever your private little fantasy may be. Maybe there's no single moment. But when the time comes, it is then I think, that you want to see yourself as part of a process, to know that something came before and something will come afterwards and maybe along the line there was a person of consequence - a king, a scholar, a great warrior or maybe a giant of a man with a white beard and a proud look in his eye who exists only in your imagination.