THIS WEEKEND marks, for all practical purposes, the end of summer--and not a day too soon. There have been years when it was possible to regret the passing of summer, but not 1983. Too brutally hot, too dry and too long, it was bad for the farmers' crops and the city dwellers' tempers. The pollen season has now arrived, of which the best you can say is that it's usually relatively brief. That will end, preferably sooner than later, with a cold front from Canada. That is not the least of the many Canadian contributions to the quality of life here in Washington.

The rhythm of life changes at this point in the year. Schools and colleges are opening, and it is the school calendar that sets the pace to which most Americans march--if only by force of long habit. Summer is over and now things get serious. Shortly there will be a snap in the air to exorcise late summer's torpor and, you are entitled to hope, revive baked-out brain cells and bring wilted spirits and imagination back up to normal operating voltage.

The heroes of the past summer were the tinkerers who, over the past two generations, invented air conditioning. The term itself was introduced, according to the reference book on the shelf, by one Stuart W. Cramer in 1907; he was trying to control humidity in textile mills. But, contrary to clich,es on the subject, technology usually disperses itself rather slowly. On hot nights half a century later, people still slept on their porches, in their yards and in city parks to escape their suffocating bedrooms. It wasn't until the 1960s that inexpensive window machines--and, let us not forget, inexpensive electric power to drive them--put air conditioning within the reach of most Americans.

Of all the technological changes that have swept over this country in the past several decades, air conditioning has done more than any other to change the character of Washington's daily life in that half of the year that begins on May Day. Before those machines arrived, anyone who could possibly manage it fled to a different climate. Those who remained resigned themselves to months of moving slowly and looking for shade. Government offices followed a ritual of closing early as temperatures rose. Other offices might as well have closed, for all the work that got done on those afternoons.

No doubt there is much to deplore in modern technological society. But after a summer like the one now departing, it is hard to pass that box in the window without giving it an affectionate pat.