A veteran marathoner, an ambitious fellow who trains 60 miles a week, has done several 50-mile races and who subscribes to seven running magazines, once told me that you aren't really a runner until your sweet forms icicles during a wintertime run.

I was elated to hear this, because I am an icicle man. Last winter, especially during late December and January, I needed only about five miles before icicles would begin descending from the frames of my glasses. The sweat would roll from my head, catch on the glasses, then freeze. The icicles were my runner's badge. On good days, when the temperatures dropped to 10 or 15 degrees, my stalactites would measure six or seven inches. Ive arrived, I said, breathing steam into the arctic air.

People who saw me doubtlessly also thought I had arrived-on the distant side of madness.For non-runners, who have trouble enough figuring us out, winter running appears to be border-line insanity. Actually, icicles or not, the cold months are the best for running.

The reasons, like the winter air, are clear. No threats of sunstroke or heat exhaustion exist. Winter runners commonly tell of the most delightful feeling of all-of thinking you could run for hours and hours. The body temperature stays lower than in summer, which means that it is mostly a question of muscle and bone fitness that determines how far you can run. The fight against humidity is a war game of the summer. Air pollution-the inversions that poison July and August-is less severe now.

The exhilarations of winter running are a delight, but getting them demauds more thought than summer running. To dress properly, the issue is less a matter of warm clothing than intelligent clothing. For your upper trunk, two T-shirts, an outer sweatsuit top and perhaps a windbreaker should be plenty. The innter shirt ought to be cotton-to absorb the sweat. If anything, most people overestimate their protective needs for winter running. This end up bundling, not clothing, themselves.

For the two heat machines-the legs-not much more than a lower sweatsuit is needed, if that. Thorough-breds like Bill Rodgers run bare-legged.They arrive at races in warmup suits, but that's it. What they do pamper are their hands. Rodgers even wears gloves when the weather is in the 50s. For nonthoroughbreds, a pair of socks to cover the hands is plently. Or two pair. Socks are better than gloves because the fingers can share their heat with each other.

It is crucial, also, to wear a hat.We are hot-headed creatures, which means that a fair proportion of body warmth escapes through the head. The colder the day, the smarter you are to wear a hat that covers the ears.

Fashion-plate runners have trouble in winter because it is all but impossible to affect the stylish look while encumbered with so much clothing. While waiting for spring and the new line in running togs, they might as well forget about impressing the world with their sartorial elegance. I've never seen a well-dressed winter runner.

An achievement worth crowing about is passing through the winter without fracturing a bone on the ice. Falls are common at this time of year for runners and everyone else. No amount of horse sense is enough to offer full protection, because often the menacing ice lays under a film of snow.

I have seen runners land on their heads because they wouldn't slow up when going over ice. In last winter's Bethesda Chase, runner were warned at the starting line about an underpass that had icy footing. Everyone took note, but when the pack reached the underpass more than a few runners who didn't want a sacrifice "a good time" went down for a good spill. Climbing over the bodies turned the event into the Bethesda Steeplechase.

For those who dress sensibly and are cautious about their footing, one other problem supposedly persists-inhaling the cold air.But this is actually a phantom problem: the lungs do not freeze. Studies reveal that by the time the outside air reaches these inside chambers, an incredible warming process has occurred. The time is only an instant but that is sufficient for the feezing air to be heated to a temperature compatible with the lungs. I suspect that many of those who profess to have tender lungs and therefore can't run in the cold are looking for an excuse to sit out the winter.

That's too bad, because this time of year is easily the most enjoyable for running. I remember a morning last winter during a dawn run when a heavy snow was falling. Only the tamping of any shoes hitting the snow could be heard. All else was stillness. The whiteness dazzled the eye. The cold braced the lungs. The winter absorbed the spirit. Everything made sense. The icicles, too.