THE URGE TO package summer, to "put it up" in jars and bottles, was originally born of necessity. Put it up or starve along about the end of January was the rule. Now that technological wizardry has skewed the seasons and made summer produce available in the dead of winter, the urge has atrophied somewhat.

But vestiges still lurk inside even the most modern of us, mostly in the form of a sudden need to can a few tomatoes or make a few pints of jam or chutney to give away later. The urge, if it hits at all, usually comes in August, when the light changes just enough to begin suggesting fall, and when the garden is overflowing with wonderful things.

Because their relatively high acid content enhances preservability, all fruits and tomatoes can safely be put in jars and preserved for the winter without a lot of expensive or complicated equipment. As some tomatoes may be on the acid borderline, however, the US Department of Agriculture now recommends heating tomatoes to just under the boiling point before they are packed into jars. The heat destroys molds and other organisms that can reduce the acid content of the tomatoes while they are stored, and possibly cause spoilage. For more information, contact your local extension service listed in the phone book under county government.

Low-acid vegetables like corn and beans, however, are more complicated to preserve. If you have a big garden and intend to do a good bit of preserving, the first piece of equipment you need is a good book on the subject. "Preserving," part of the Time-Life Good Cook series, is one such book. It includes recipes and methods for all kinds of preserving, not only canning. The extension service is another invaluable source for canning and preserving information.

The simplest method of preserving high-acid foods is to pack them in jars and then sterilize them by placing them in a bath of boiling water for a specified length of time. All you absolutely must have to accomplish this are the jars and some way of sealing them, and a kettle large enough to hold your jars and allow them to be covered by an inch or two of boiling water. Some kind of rack, improvised or not, is needed to hold the jars up off the bottom of the kettle so boiling water can circulate underneath them. Some people use extra jar tops for this.

Of course there are also all kinds of special equipment to make your preserving task easier and more expensive, beginning with kettles designed specifically for canning. They come with racks that hold the jars steady while they boil, and with lids. A canning kettle that will hold nine quart jars at once will cost about $30. (If you intend to use quart jars or larger, make sure your kettle is tall enough; many of them aren't.)

Glass canning jars, decorated prettily or not, cost $5 or $6 for a dozen of the 8-ounce size, complete with lids and screw bands. Lids and screw bands can be purchased separately, and there's always a sale going on somewhere for both jars and tops. Recycled jars like peanut butter jars, for instance, can't be used for canning because they usually aren't manufactured to withstand boiling. One expert canner I talked to says she prefers wide-mouth jars because they're easier to work with.

In the not-necessary-but-useful category are funnels and jar lifters. A wide-mouth funnel made especially for getting food into jars is cheap--usually under $2--and saves lots of sloshing. Sloshing is fairly serious in this case, since a proper seal between jar and lid can't be made if either is sticky or dirty. Jar lifters are nifty contraptions that allow you to grip the jars and extract them from boiling water safely. They cost around $3. Of course you could also use your barbecue tongs.

Jellymaking involves letting juice gradually drain out of cooked fruit. You'll need some straining material such as cheesecloth, plus some kind of stand to hold up the cheesecloth while the fruit is draining. There are special jelly bags and stands sold, for about $4.50, to do this job.

Some stores sell beautiful unlined copper "confiture" pots for boiling up fruit and sugar to make jams. The copper reacts with the acid in the fruit in a way that helps to brighten the color of the jam. If acid foods are left to sit in unlined copper, however, this friendly reaction can turn unfriendly and cause illness.

Foods low in acid--and this includes most vegetables and all meat, poultry and fish--need a processing temperature higher than the normal boiling point to be safely preserved. A pressure canner, which contains the steam instead of letting it escape into the air, makes possible a boiling point higher than 212 degrees. Pressure canners are not cheap--about $80 for a canner that will hold seven quart jars. But they should last a lifetime, and they can be used for regular water-bath canning, or for boiling spaghetti. Good neighborhood hardware stores often are the best source for this and other canning equipment.

If you should inherit an old pressure canner, make sure the gasket that seals top to pot is intact. If it isn't, you'll see steam or condensation escaping. Replace it if it's worn out. The pressure gauge also needs to be checked every couple of years--a gauge that shows a higher pressure than actually exists can allow foods to be underprocessed. Your county extension service will check the gauge for you.