On 15th Street, in the heart of downtown, a storekeeper has set out a Christmas tree on the sidewalk. It has not yet been trimmed and on a dreary, rainy day, its spindly undecked branches form an acute and lonely picture. And somehow fitting for the season.

For years now the sociologists an psychologists have been musing about the Christmas traumas - that time of year when private depressions mount and the suicide rate rises. It is not supposed to be that way, of course. All around us sounds the message: Be Jolly! Be Merry! Be of Good Cheer!

Perhaps the problem lies in our being constantly bombarded by such synthetic admonitions. To admit to feeling anything other than total happiness is to concede failure, terrible and personal. Our entire culture, it seems, conspires to give us a collectives sense of guilt if anything is even slightly awry in our lives. The radio blares the message, the TV beams the picture, the shopping center loudspeakers boom the word: Rejoice! From childhood we have had hammered into us the image of that bubbling, laughing barrel of mirth, Santa Claus.

All this, I submit, is very American. What reading I can find about the model for our own red-suited Santa, the original St. Nicholas, suggests he could be quite a formidable old fellow. He was supposed to have come from Turkey, and won fame as a worker of miracles. His particular feat, oft-repeated, was saving children from some tragedy. In time, the Germans transformed St. Nick into Father Christmas. And then the Dutch made him into Sinter Claes. We did the rest. Presto. Santa.

But even those mythical versions of the ubiquitous gift-giver made him out to be a rather stern character. He could punish as well as reward. And awarness of sin was very much a part of his make-up.

I had thought we could blame Dickens for setting the impossible standard of requiring everyone to be instantly happy and hearty. But I find, on re-reading many of his Christmas stories these past few days, that I was wrong. Dickens was a prodigious producer of those tales. Today, we remember mainly only his "A Christmas Carol," with the memorable Scrooge and Old Marley and Crachit family. But he wrote many, many more: "The Seven Poor Travellers." "The Holly Tree." "The Wreck of the Golden Mary." "The Perils of Certain English Prisoners." "Tom Tiddler's Ground" and "Mugby Junction," among them.

Read these over now and you'll find a suprisingly bleak landscape. Death and doom, loneliness and despair are common themes. Thus, Dickens:

From "The Seven Poor Travellers," 1854:

"In the year one thousand seven hundred and ninety-nine, a relative of mine came limping down, on foot, to this town of Chatham. He was a poor traveller, with not a farthing in hispocket. He sat by the fire in this very room, and he slept one night in a bed that will be occupied tonight by someone here.

"My relative came down to Chatham to enlist in a cavalry regiment, if a cavalry regiment would have him: if not, to take the King George's shilling from any corporal or sergeant who would put a bunch of ribbons in his hat. His object was to get shot; but he thought he might as well ride to death as be at the trouble of walking . . .

"You are to know that this relative of mine had gone wrong, and wild. His heart was in the right place, but it was sealed up."

In the end, as we all know, Dickens always did manage to provide a happy ending. In our day with our Santa, and our Christmas customs, we skip the sad stuff altogether and begin at the ending where joy and happiness reign. You'd better be happy, damn it, even if it hurts. No wonder we seem to be paying an increasingly high price for such mass neuroticism.

Even as I write, literally, the afternoon Star arrives carrying the front-page, eight-column headline "Battling the Holiday Blues Can Be a Major Problem," with a two-column deck reading: "You Must Remember That You Are Not Alone."

In glancing at it, I see they quote a mental health expert about the causes of Christmas depression and anxiety. I don't know about the experts, but I offer my own purely personal and unscientific views. I suspect there are many, like myself, who find Christmas a bittersweet experience, a time of pain as well as pleasure. And most of all, a time when our strongest memories tug us inexorably back into our past.

Two years ago, on Christmas Eve, I sat with my father in Connecticut tape-recording his reminiscences. He was fatally ill, and knew it, but he had had a wonderfully rich and full life. What struck me then, and comes over even more forcefully now, was that the single most vivid memory he summoned up that day involved his own father and a Christmas incident in his childhood. This was in Gainesville, 6 a.m., a small town nestled in the foot-hills of the Blue Ridge Mountains.The year must have been about 1909.

"I've always regretted I didn't know him better," he was staying. "Of course I was only 13 when he died. But one thing that stands out in my memory most vividly about him, and I've never forgotten it and I never will, was when I was a very small child. I guess I must have been around five years old. There had been a Christmas party for children in the basement of the Baptist Church. A tree, and they were giving out presents. My father had gone to the service upstairs. Every child was supposed to get a present under the tree. Well, with the older children there, it was just like a stampede. They just pushed everybody aside and grabbed everything, when my father came down there I was sitting by the Christmas tree just bawlin' my heart out, just sobbing.

"And he said, 'What's the matter? I said.' When I got to the tree there wasn't anything left. No presents.'"

"Well, I never saw him as upset as that there was one particular package that I wanted. I described it to him, what color it was and all, and nothing would do but for me to have that. My heart was set on it. He took me by the hand. By that time it was night, but the stories were still open. We tramped all over town. He was trying to find that exact package I wanted. And he would say, "Is that it?"

"No, he doesn't want that, he wants just this."

"We went from store to store trying to find that. We never did. He finally persuaded me to take something else. But I figured that a father that would take that much trouble and have that much sympathy for a crying child at Christmas time was a pretty good man. And I've never forgotten it.

As this season approaches, we usually hear solemn sermons about the increasing commercialization of Christmas. I find, as I get older, that I can settle for the sound of the cash register much more than the forced holiday. For me, Christmas means both love and loss, sadness and warmth. And I don't mind saying I celebrate mine with a measure of them all.