IF IT MAKES you any happier, we will go along with the crowd and celebrate today as the arrival of the fall. Technically, of course, this is the time when the sun begins its weary roll across the equator, so we're all quite safe and proper in welcoming autumn, and in throwing a few festivals, reciting Keats and Donne, and going through all the other familiar rituals that will accompany the lie. For it is a lie, you know. Equinox, schmequinox - September might as well be spring.

Just for the record, the normal monthly average temperature for Washington in September, based on the period from 1941 to 1970, is 70.6 degrees Fahrenheit - higher than May, and only slightly cooler than June. The normal monthly maximum temperature for September during the same period is 80.2; the normal monthly minimum, 61. The highest temperature of record for Washington in September is 104. All of which is to say that September is a lovely month, but no way is it fall.

It seems to us, therefore, that we all might be better off, and a good deal less disappointed, in not recognizing this day as the beginning of fall, no matter where the sun happens to be rolling. Instead, we might simply go ahead and take September on its own limited terms, avoiding considerations of summer of fall and celebrating individual holidays as they occur, such as the death of Pepin the Short (the 24th); Hirohito's first U.S. visit (the 26th); and the Feast of the St. Thiemo, patron of engravers (the 28th). On the 29th of September Gene Autry was born, and on the 30th, ether was first used for a tooth extraction. Today you might wish to observe the occupation of Jersey City by the British in 1776.

Whatever celebration you choose, we urge you to enjoy yourselves for the next few days, knowing perfectly well that that there's no point in hailing autumn until at least the second week in October. By that time the Yankees will be winning the Series, the kids will be pleading for Christmas toys they see advertised on television, the first winter cold will be clogging our sinuses, and we'll know we're in season.