The Downward Slide of the Zipper, and other tales of wardrobe woe

The Mystery of the Disappearing Zipper and The Case of the Gaping Placket are not, as you might surmise, a couple of hitherto unknown Agatha Christie stories. But don't they make quite a team? And if you added The Omnipresence of the Elasticized Waistband, you would have a trilogy you could give the overall title of Disaster in the Fitting Room.

Seriously now, and although no one has asked us for comments on the way clothes fasten (or do not fasten) together these days, it seems time to take stock of what looks like a deteriorating situation.

When did you last see a skirt that closed smoothly with a well-placed zipper, instead of one measly button over the bulge of an open side pocket? How often does that badly-sewn-on button pop off, and under what embarrassing circumstances? When, we might also ask, did you last buy a dress that wouldn't grab your middle with a tight band of elastic?

But perhaps you settled for a drawstring. That's the easiest way in and out of a one-size-fits-all. Maybe it does fit, and maybe it doesn't. Could be that too much is taken for granted.

The fact is that since the demise of the back zip, an occurrence that coincided roughly with the departures of the bust dart and the underarm gusset, things have been steadily on a downward slide.

Not that anyone who ever wrestled with a back zip misses it. All the same, we should ask ourselves if we are truly better off now.

The A-line dresses of the late 1950s needed back zips, and dresses that had fitted waists needed zippers up the side. They all went away. Enter the 1960s, with its beads and bangles. Unfettered era that it was, it celebrated the human form. We had clinging fashions: body shirts, cat suits, and so on. Although some of these garments were of stretch material, many of them still needed zippers. Hardware trims were big, and the industrial zipper was discovered as a decorative accent. This meant that zippers were positioned in places where they were really not required. But no matter, zippers were still doing fine.

What brought about what a spokesman for Talon, a leading United States manufacturer of slide fasteners, describes as ''the decline of zippers in women's apparel'' was the arrival of the kind of loose, free-flowing clothes that have recently become popular. Carried away by the casual lines of present-day fashions, clothing makers have come to regard the body as an object to be wrapped, tied, and provided with the occasional hook and eye, and that's it.

This attitude is regrettable, as anybody who has experienced The Great Divide when wearing a wraparound skirt on a windy day can tell you (back wraps being especially treacherous). Adding snappers to keep the overlap of a wrap skirt under control would no doubt help, but who thinks of that when the labor costs are accounted?

As to those elasticized midsections, they do look suspiciously like inexpensive cop-outs for a more finished waistband. But industry specialists say that a length of elastic run through a casing doesn't necessarily cost less than other methods of indicating where a waist is.

As matters stand, 9 out of 10 dresses, and not all of them blouson styles, come with these elastic inserts, and they are almost invariably in the wrong place. Besides being too high or too low, they are unkind to the flesh and create rolls of it where rolls are least desirable.

None of the above is, however, likely to be heard, discouraging as that may sound. Judging by the influence exerted by the shroudlike fashions of the new school of Japanese designers, the zips, snaps, hooks, and even the buttons we knew are imperiled. We may be going back to the cave woman's bone pin.

That would be a disappointment for Whitcomb L. Judson, who created what he called the ''clasp locker and unlocker'' circa 1891, and for Col. Lewis Walker, who later developed Judson's primitive slide fastener into the modern zipper. For an ingenious invention that ranks right up there with the tea bag, the zipper deserves a better break than it's getting in fashion today.