THE SUMMER of the Swamp (as the Dog Days of 1979 will be known in these parts) has receded grudgingly into the murky backwaters of Washington memory. You will be happy to know -- those of you who sprained your brains looking for a de-humidifier -- that it's now time for humidifying.

Yes, it's a whole new ballgame, folks, and we've got a great lineup for you. Playing the center position on this year's team is Static Cling. At left guard, Desert Mouth. And making his first appearance as a forward, an old favorite and a real sport, Shocks Doorknob.

We'll now rise for the team song, "Sparks Fly When I Touch You."

There's a perfectly sane reason why things dry out in winter. There must, be after all, some explanation for those mid-December mornings when the tongue cleaves to the roof of the mouth and the tonsils scream, "WATER!"

Here's the reason, best I can figure out: In winter, humidity is on a cruise somewhere in the tropics.

Fortunately, there is ersatz humidity, which usually comes from a humidifier.

In the winter, when humidity drops in tandem with the falling mercury, indoor moisture levels are especially low. Humidifiers, either the portable room models or those attached to the furnace for wholehouse comfort, are designed to put moisture back into the air.

The National Bureau of Standards recently studied humidifiers for energy efficiency, raising the question of whether the use of a humidifier, while it might make the living area more comfortable, can also result in increased energy use.

Water absorbs heat. When it is released into the air, explained Robert Wise, an NBS engineer, the furnace must work harder to vaporize it. It's one of those mysteries of physics engineers are trained to understand.

Wise said some people who use mechanical humidifiers could notice an increase in their winter heating bills.

Humidifier manufactures argue, however, that whatever costs result from using a humidifier are offset by better health and less damage to furnishings.

"Lump those things together," said Gautum Dutt of Princeton University's Center for Energy and Environmental Studies, "and they might completely overwhelm the energy question."

Gutt says humidification "reduces the incidence of bronchial problems."

But before you rush out and buy a humidifier, consider those things you can do to increase the relative humidity in your house without one. Such as turning down the thermostat.

Humidity, as most things, is relative. If the air contains an absolute moisture level of, say, 30 percent, its relative effect will be greater -- you will feel it more -- if the temperature is 68 rather than 72 degrees. The same principle holds true in the summer, if you turn it inside out a bit: hot days of 50 percent humidity become unbearably hot days when the humidity climbs to 85 percent.

With a decent humidity level, somehwere between 30 and 50 percent, 68 degrees will feel like 72.

Weatherstripping, says Gutt, will also improve the moisture level in the house. Tightening the house will both trap humidity in and keep dry cold air out. (Some new houses have been built so tight, government studies have found, that they develop excessive humidity and indoor air pollution problems.)

If you do buy a humidifier, "buy the one that will put out the most moisture," Wise suggests. "But also buy a humidiestat. You can put out more than you need."

It used to be (and in some countries it still is) that a humidifier was a tray that hung on the radiators. You water them in the morning along with the spider plants and the Wandering Jews. But we live in a mechanical age.

Stores seem to be better stocked with electric humidifiers than they were with de-humidifiers. A number of different makes and models are available at most department and household stores, at prices ranging from around $30 to more than $100, depending on how large a humidifier you need. (A 14-gallon tank is about sufficient for a 2,000-square-foot house.)

Humidistats, if they are not built into the humidifier, are available for as little as $4. You can also buy chemical treatments for water reservoirs to staff off bacteria growth.

There are two basic types of humidifiers: portable room models and those that attach to the furnace to supply moisture throughout the house.

Among the former, the Presto humidifier, for instance, made by National Presto Industries and sold at appliance stores in the Washington Area, is made in two basic sizes; one with a 10-gallon size tank and a compact model with a 2-gallon tank. Inside, a large belt of porous material turns on a roller. The belt picks up water at the bottom and brings it to the top where a fan blows moisture into the air.

The more expensive portable models have an automatic shutoff and a light to tell you it's out of water.

Some furnace-attached humidifiers require installation by a professional. Others, however, are designed for do-it-yourselfers. The Goodbye Dry, sold in the Washington area at Hechingers, is a low-voltage system. The 24-volt relays attach to a transformer that can be plugged into a standard wall outlet. The humidifier fits under the warm air duct and the feed line has a piercing valve that is simply tightened around a cold water line. A small hole is cut into the duct. A rotating sponge wheel releases moisture.

A similar humidifier is the Pulse, made locally in Beltsville, Md. It uses low voltage and a transformer, is attached to the furnace plenum, but delivers moisture through an atomizing or spray mechanism.

A heat sensor in the furnace and a humidistat in the return air duct allow the humidifier to operate only when the furnace temperature is above 107 degrees or when the humidity level has fallen below the preset level.

Both retail in the $60- $70 range.

Or you might just put the money into a cruise of your own.