Building a backyard skating rink requires care and patience

''Hey, let's build a skating pond in our yard this winter,'' a teen-ager says , watching the first snowfall of winter. Well, why not? We did and it gave the teen-agers a way to use up some of that excess energy and made a lot of fun for the family in the bargain.

''But what about my lawn?'' you ask. ''An ice rink in winter for no grass in summer? No way!''

Don't worry, you won't lose your lawn. We've had a skating rink every year for the last 10 and our grass is just as green and thick during the growing season as when we didn't have a rink in our backyard. The trick is to spread a commercial fungicide, either before you make the rink or after the first thaw in spring. A fungicide gets rid of any mold spots in the lawn.

Obviously, you can't start the ice rink until the ground is frozen to about six inches anyway - and you need snowfall if you don't want to use sideboards to contain the water. Snow serves to form the sides of the rink instead of the boards.

When the ground is ready, build up the edges of the rink with a mound of snow by using a push shovel or stiff-bristled broom. The idea to use sideboards is good if the snow isn't particularly heavy in your area.

Next, tamp the mounded snow down around the edges. Then, using a hose, spray the edges so as to form a hard ice crust and prevent the water from leaking out the sides. It's important that the edges be watertight.

Try to make the skating area as level as possible to keep the water from rolling down into a low section of the yard. You might need to bring in extra snow to fill any low spots. Then lightly spray and tamp down the snow in the pond area to form a slush base.

Begin watering the base to get a smooth surface. Since the water from the hose in winter is above freezing, about 45 degrees F., the base could thaw in spots to show the ground beneath. To eliminate the hose water pressure from digging these holes, keep moving the nozzle from section to section on the ice.

Continue building up the ice, a thin layer at a time. Even while building up each layer, you may need to bring in more snow to fill in any low spots. Take the time to do a good job.

When a thin ice crust forms, stop watering and allow this layer to freeze thoroughly. If you flood too much at this stage, air gets between the layers of ice and cracks and crumbles the top layer.

Between waterings, don't turn the faucet off. Either place the nozzle outside the rink and allow a trickle of water to run from the hose, or disconnect the hose and take it indoors after each watering. Otherwise, the water in the hose will freeze.

The ideal time to flood the yard is at night when the temperature is low. Don't let the water run all night for a ''quick rink'' the next day. Stick to a thin layer of ice at a time. You'll be a lot happier with the finished product.

Try to get about a 3- to 4-inch thickness of ice, enough to cover the rough slush base and keep the skate blades from breaking through to the ground.

In the spring the ice will melt before the ground thaws completely. So to minimize standing water, make breaks in the edges of the rink so the water can drain off quickly. Since the grass roots are dormant in the frozen ground anyway , water only hastens the thawing process.

Because new grass needs as much oxygen as possible, you need to reduce any standing puddles of water. To speed up the thaw, simply break up the ice and cart off some of the larger pieces.

As the water begins to drain out of the rink, get rid of any stagnant puddles. Usually, the soil is thirsty in the springtime and absorbs all the water it can get.

With a few days' work, you can build an ice rink for months of wintertime fun as well as provide the grass with plenty of water in the spring.