Just as some people know that food consumed in the back pantry is not as fattening as food eaten in the dining room, I know that food eaten outdoors has no calories. As exercise, breathing fresh air, of course, offsets the fatty content of five pieces of chicken, a bowl of potato salad and as much chocolate cake as you can get away with.

I also know that the great outdoors is as flawed as the rest of us: bugs, slugs, gnats and bats and picnic cloths as well as candles blowing in the wind. Efforts must be made to contain nature.

First bugs. Spray the area where you'll eat both long enough before the guests arrive so the smell evaporates, and short enough so the bugs are still gone.

Or buy a mosquito coil - a modern version of the old-fashioned sticks of punk - which will burn from five to seven hours. A packet of eight Mosquito Coils is $1.20 at Mikado, 4709 Wisconsin Ave. NW.; under the name Pic, four coils are 99 cents at Johnson's Flower Center, 4020 Wisconsin Ave. NW. If you are both rich and ravenous about eating outside, you can invest in a Rid-O-Ray, an electric bug-killer which comes in two models - $109.95 and $139.95 - at Pool & Patio, 1042 Wisconsin Ave. NW.

If you're picnicking on the grass instead of at a table, Indian paisley bedspreads make bright, inexpensive picnic cloths. Anchor them with pillows, bricks or lazy guests, but forgo stemmed wineglasses. They tend to tip over on the lumpy ground. Nor should you leave the remnants of dinner about. The food attracts slugs, which do not attract anyone. Since slugs are notorious beer lovers, you could try the alternative of setting up a bar for them in another part of the garden . . . low dishes filled with beer into which they can fling themselves.

There are all sorts of expensive torches and stick-in-the-ground candles, but votive candles and kerosene lamps, both available and cheap at the neighborhood hardware store, protect flames from the wind and, although I suppose you could knock over a votive candle, it's hard when they're already so close to the ground.

Even cheaper would be to emulate the residents of Santa Fe, N.M., who, at Christmas time, light the streets with hundreds of short candles anchored in small, sand-filled brown paper bags - tops turned down, of course. (Need it be said that caution should be exercised with all fire - candle, lamp or barbecue?)

One other thing I've learned about entertaining out of doors is to always seat the Dedicated Gardener guest next to your weediest flower bed. First it will be one weed and then another.The guest will rise to the challenge as a true gardener must, and by evening's end, you will have a clean flower bed.