A terrarium can be a place of magic for a child-a garden growing in a fishbowl or other closed glass container in which a collection of similar plants is grown. With simple equipment and few instructions, a child can construct his own magic garde.

To begin, you will need a glass container, a cover of glass or plastic, small plants, pebbles, charcoal chip, soil and a mist sprayer.

A terrarium should be made of clear glass because colored glass filtrs our needed light. Plastic becomes clouded with age and not only filters out light but partially obscures the plants. The container should have a large enough opening; those with a small openings are difficult to plant and require special tools. Use a fish bowl, candy jar, brandy snifter or aquarium.

The number of plants needed will depend on size of the container. Don't crowd the garden. The plants will grow and fill in the space. Do not combine woodland and tropical plants because their requirements differ.

Most useful are miniature foliage houseplants such as fittonia, creeping fig, small-leaved ivies, variegated euonymus, pilea, peperomia, philodendron, baby tears, small ferns and parlor palm.

Most flowering plants are not suitable for the humid atmosphere of a terrarium, although miniature types of African violet and wax begonia can be successfully grown. The miniature gloxinia, sinningia pusilla and its hybrids, and the miniature begonia prismatocarpa are especially effective. Usually, one flowering plant set among the foliage is sufficient. Begonia prismatocarpa grown by iself in a small bowl is a delicate bouquet of tiny yellow blossoms on light green foliage.

Begin by washing the container with soapy water. Then place about an inch of moist pebbles for drainage in the bottom of the container. Sprinkle a light layer of charcoal chips over the pebbles; shake the container to settle the chips in the drainage material. Then pour in abour 2 inches of soil. Use a loose gritty potting soil or a special terrarium mix, which can be purchased at garden centers. The total depth of soil and drainage should be about one-fourth the height of the container.

Plan ahead how to place plants to minimiz the amount of handling. Taller plants should be set in the center or to the rear of a container that will be viewed from only one side.

Scoop out a small hollow in the soil for each plant. Set the plant in the hole and use a pencil or pointed stick to move the soil back in the place around the roots and firm it gently. When placed, plant leaves should not touch the glass.

After plants are in place, give each a small amount of water from a meat baster. Brush soil particles from leaves. Mist plants and allow some of the water to trickle down the inside of the container to remove dust of soil particles.

Then, cover with a lid, pane of glass or plastic wrap. The purpose of the cover is to maintain moisture by condensation within the container.

Plants will grow best if the terrarium is located in bright light but never in the sun. A room temperature of 70 degrees is satisfactory.

For the first few days, keep close watch to assure that the terrarium has enough, but not too much, water. If beads of moisture condense on the inside of the glass so that you can barely see the plants, remove the cover and leave it off over night. Some of the excess moisture will evaporate. It may be necessary to repeat this two or three times. A satisfactory balance has been reached when only a thin film of condensation appears on the inside. If there is no condensation at the outset, mist the plants and soil, or water sparinlgy with a few teaspoons of water and replace the covr. A covered terrarium may need water only once or twice a year. Open it briefly now and then to give the plants a breath of fresh air.

Plants in a terrarium will grow for long periods without feeding, deriving nutrients from the original soil used. If plants are fed, they are likely to outgrow the limited space. What you want to achieve is a miniature landscape. Some plants that are especially vigorous will need to be trimmed so that they don't usurp all the space, or you may want to remove them entirely. Remove any dead foliage or flowers.

The terrarium can be a miniature tropical scene or a tiny greenhouse. If planted properly, it is self-maintaining. The magic is that once the cover is in place on terrarium, nature takes over. Moisture from on your evaporates, condenses on the glass, then "rains" down on the plants and soil. The cycle is repeated indefinitely. And while you enjoy the experience of the magic garden, you observe nature at work and learn a lesson in ecology.