The conventional wisdom on preserving the contents of an open bottle of wine is that it can't be done -- so, once the cork is pulled, drink it or lose it. While this is generally true, with some small effort, you can have your wine and drink it too.

Although almost all of the wine sold in this country is in bottles of 750 milliliters or larger, there is a middle ground between the decision whether to forego wine or to open a full bottle and possibly waste some portion of the contents. For a very small investment of time and money, half a full bottle can be drunk and the other half saved to await another day. The keys to the technique are an inexpensive hand corker and a supply of empty half bottles.

Before opening the bottle, there are a few things which must be done. First, wash an empty half bottle in boiling water. Dry it carefully and let it cool. Cooling can be hastened by running progressively cooler water around the outside of the bottle. after cleaning the top of the full bottle, remove the cork. For our purposes, this is best accomplished with an Ah So-type cork puller that grips the side of a cork rather than puncturing it, but can be done just as well with a corkscrew, provided the screw does not break through the bottom of the cork.

Working as quickly as possible, fill the half bottle to a level that will leave 1/4 inch of airspace between the wine and the cork when it is placed in the bottle. Using a hand corker, replace the cork from the full bottle into the half bottle. The hand corker is an extremely simple device which compresses the cork and allows it to be placed inside the bottle without damage to the sealing surfaces.

If your equipment and preparation have been sanitary, these steps should preserve one-half of that bottle for the future. Because the wine in the half bottle has been disturbed, it will be "bottle sick" for at least three months after this procedure and will not taste nearly as good as the first half if opened too soon. Given time, though, the wine in the half bottle should recover to the quality level of the first portion. The half bottle should be stored on its side and should be inspected periodically to assure that the seal is not leaking.

I have used this technique with equal success on a variety of wines, from 10-year-old Bordeaux to non-vintage bottles. The technique works equally well with red and white wines, though low-acid white must be handled very carefully to avoid enhancing oxidation. As wines grow older and more delicate, chances of success lessen. Until familiar with the techniques, one would be well advised to stick with young, sturdy reds.

If you intend to follow this method to save half of a valuable or unusual bottle, you may wish to take an additional step to make certain the second half will be as good as the first. Instead of merely replacing the cork from the large bottle to the small, it can be placed in boiling water for a few moments; better yet, replace the cork with a new one from a home-winemaker supply house.

Recorking fine wines is a procedure of which most wine lovers have heard, but few understand. The life of the finest dry reds and some sweet whites can exceed 100 years; the life of the finest cork is limited to 25 or 30 years. cThe solution for this disparity is recorking wines as they approach a quarter century of age. Many leading chateaux will perform this service for a modest fee. However, you can recork your own.

Three years ago, a friend in the wine business offered me several cases of Chateau Gloria 1970 for $30 a case, a price that was then about one third of retail.When this wine was originally corked, the automatic corking machine had a burr that sliced each cork along its entire length. In the following months, gravity did its job, and each bottle began to leak. The task of recorking some 50 bottles of wine, each of which had to be "topped off" with wine from other bottles, required planning to be successful. To date, every one of those "Gloria Recorks" tried has been superb.

I have since recorked many types of wine; I have always followed the basic steps outlined here. Thoroughly clean the top of any bottle to be recorked -- it is mandatory that the area at the lip of the bottle not contain foreign matter which could contaminate the wine. Depending on the number of corks involved, dissolve one or two commercially available sulphur-dioxide tablets in boiling water and immerse the new corks in this solution for 10 or 15 minutes. While waiting, sterilize the action of the recorker by pouring boiling water over it.

Place a new cork in the action of the recorker. Remove the old cork as quickly and carefully as possible. If there has been a loss of wine, top off the bottle with more of the same wine or fill the air space with sterilized glass beads. It is of critical importance that the wine be open to the air for the shortest possible time. Immediately replace the cork. In placing the new cork, air pressure will build in the head space. This can and should be released by sliding an Ah So-type cork puller down the edge of the cork until the seal is broken and the pressure released.

Affix a new foil capsule after the recorked bottles have been on their sides long enough to assure that there will not be any leaks. As with decanting from full to half bottles, recorking disturbs the wine. Again, at least three months should pass before opening the wine.

At one time, home-winemaker-supply houses were quite common in this area. Their number is decreasing. A very good source for all of the items mentioned in this article is The Cellar in Fairfax, Va. Readers further out in Maryland should be able to acquire needed supplies through Wine Craft in Randallstown.

There are several types of corkers available, their prices ranging from $6 to $15, depending on brand and design. The sulphur-dioxide tablets, known to home winemakers as campden tablets, cost less than $1 for a bottle of 50. Corks are priced by length -- prices run from $1 to $2 a dozen. For the very best Bordeaux, corks should be two inches in length and may have to be specially ordered. The easiest way to obtain a dozen or two empty half bottles is to buy them full of wine and drink them. Replacement capsules, if desired, are available in both plastic and foil at a nominal cost.