ORDINARILY WE TRY NOT to appear alarmist about the matter of cultural trends, but a number of events have occurred in the past couple of weeks indicating that some very old and honored traditions and institutions are being smashed left and right. The Vienna Boys Choir, for example, will be silenced this Christmas for the first time in 500 years, thanks to the discovery of an Austrian child-labor law forbidding children under the age of 15 to work during school holidays. It is believed that the family of a former choir member snitched to the authorities after the boy was thrown out of the choir. This at least preserves the tradition of the dog in the manger. Still, it is hard to imagine Christmas without those bell-voiced sopranos. Yet, so it will be.

It will also be "goodbye, sphinx" in Egypt if the Egyptian authorities don't get off their haunches and begin restoration of the 5,000-year-old whatnot. "The sphinx is sick," reports the daily paper Al Akhbar, in reference to the fact that the outer layer of the lion-bodied, king-faced creature has been peeling off. Already the sevenfoot nose has been missing for centureis (Napoleon's prank, it is said). The left eye is drooping as well-the work of the sandy winds, or perhaps of a new young Ocdipus who has come along to collapse the beast by answering that simple-minded riddle again, Whatever the cause, another institution is going fast.

Over in London, The Times has suspended publication indefinitely, thus frustrating all the Londoners who planned to send quirky letters to the editor this Christmas. And down in Louisiana, on Jan. 1, the nickel phone call will go the way of the five-cent cigar. To stop everything, the institution of the wild and crazy teen-ager seems to be injeopardy as well. In an opinion poll taken among 318,000 leading high school students, 62 percent said they abstained totally from sexual activity, and 89 percent claimed never to have smoked marijuana. Of course, those percentages may represent the continuing tradition of lying to pollsters. But if not, what's happening?

In fact, the only upholder of institutional thinking we can find in the world of late-and even this is merely alleged-is Nancy Winnie of Mahopac, N.Y. It seems that late last May, Mrs. Winnie's son-in-law, Norman Himmelein's father-in-law and law partner, taht he locked Mr. Himmelein out of his office. But evidently Mrs. Winnie did not consider that sufficient punishment for breaking up a marriage. So-as Mr. Himmelein has officially charged with the district attorney's office in Manhattan-she "made a contract to have me knocked off."

An old-fashioned gal, that Mrs. Winnie.