THERE ARE THREE things that signal fall for my sister, who called the other day: The enervating heat has loosened its paralyzing grip; she now feels like cleaning her house, and, will we be coming home for Christmas? This always strikes me as hasty -- polishing off summer, summoning a ritual of spring and beckoning the snow in a few quick seconds of conversation -- but my sister was never one to stretch things out.

When autumn comes, I like to shift gears more slowly, to savor summer's climaxes and prime for fall as carefully as for New Year's. More so, really. For those of us who march to the calendar of the school year, fall is a new cycle, a new start.

It has been a nervous summer; it began terribly with the Miami uprisings in May and the out-breaks of riots in scattered spots over the summer By late August, a vacation beckoned. Days spent with the timeless ocean, overwhelming as it tumbles and breaks repeatedly upon the seashore, somehow representing life's terrors and beauties, succeeded in putting the seal on summer. I am ready to shift into first gear for fall, officially here today.

I am ready for the light to splinter into amber rays if not quite prepared for the falling leaves.

Seeing signs of happiness in autumn may place me in a distinct minority. You realists will forgive me. Some psychiatrists call fall the "down cycle."

People approach spring and summer with high hopes, says a psychiatrist I know. "They have romantic dreams of things they will accomplish. But now the summer is over and it never quite turns out the way folks expect. There is a general letdown. Funtime is over. The symbolism is powerful."

That must hit hardest around the middle of October, though, this intense stress-time. That's when the autumnal cycle enters middle age. That's when the trouble starts, with lovers, live-ins and marriages enduring forced togetherness. That's when only the bleak November spirit confronts you upon the horizon. That's when the poor start worrying about heat and staggering energy bills ahead in the grim season.

But the beginning of the fall cycle is different. There is still much that is good about autumn's start. In mid-September, some of the diversions of summer still can be had -- tennis and bicycling, to name a couple. There's still sparkling September sunshine and the uncertainty of the temperatures -- an occasiional Indian Summer day is promised before the onset of November's blinding chillscape. Still, the smell of grass cuttings before the whiffs of a smoldering fireplace. Still time for the delight of walking in Washington, although the city services in my neighborhood sometimes dispel this potential delight.

Fall means a fresh start; a time for school kids to pledge to do better; for teacher to resolve this will be a better year; for professionals to set strategy for another leap up the ladder. There's still Skyline Drive's leaf eruption to look forward to, and our own Red Maple's tiny triumphal entry.

Still the pessimists shake their heads. Fall is so naturally conducive to dejection that many of the world's worst crises have occured then, they say. Hitler annexed part of Czechoslovakia, Mussolini invaded Ethiopia, Franco ignited the Spanish Civil War, they point out for historical starters.

So I am left to turn to the world of literature for ammunition, to a learned gentleman-poet named Paul Laurence Dunbar. He supports my little drive to increase the minority seeing signs of hope in autumn. Dunbar writes: "It's all a farce -- these tales they tell About the breezes sighing, And moans astir o'er fields and dell, Because the year is dying. Such principles are most absurd, I care not who first taught 'em; There's nothing known to beast or bird To make a solemn autumn."