THERE IS much to be said for buying a living Christmas tree this year if you arr prepared to take care of it. It could be used to start a hedge of large evergreen shrubs or small trees as a windbreak on blustry winter winds.

The winds, which usually come northwesterly from the cooler portions of the United States and Canada, have a chilling effect on the way you feel. For example, according to researchers, a 10 m.p.h. northwesterly wind will make an actual air temperature of 44 degrees Fahrenheit feel as though it were 32 degrees.

The winds also accelerate the rate of exchange between a house's exterior and interior environments, resulting in an increased demand for heating oil.

A Nebraska experiment station reports fuel savings of 23 percent in a house landscaped to minimize air infiltration over an identical one completely exposed to winter winds.

Since winter winds are often of high velocity, they also can create serious soil erosion when they blow over areas of bare soil.

The living Christmas tree should be adjusted gradually to the changed environment indoors. If balled-and-burlapped, put it in a tub. If it is in a container, so much the better. Put it in a room with good light but no heat for a day or two. Then add heat, increasing the temperature each day. When you decorate the tree, arrange the string of lights so that bulbs cannot touch the needles.

If the tree is kept indoors too long, it may become susceptible to cold injury when it goes back outdoors. Up to a week is safe enough. Have the hole already dug for planting it outdoors.

The tree should be adjusted gradually to the change from indoors to outdoors. Experience has shown that it is better to protect the tree from wind and sun after it is planted. Wind and sun draw moisture from the foliage at a time when the roots may be in frozen soil and unable to replace it. Burlap attached to poles on the south side of the tree for the rest of the winter can help a lot.

Although most prevailing winds come from the west, the wind becomes far less predictable as it bounces and tumbles over buildings and fences. Snow drifts should show how and where the wind is blowing, and you can tie strips of cloth stakes placed at different points in your yard to determine this, too. .

The windbreak can actually decrease air velocity for a distance of five times its height to the windward (where the wind blows from) and 25 times its height to the leeward (where the wind blows to).

The windbreak is placed perpendicular to the path of wind flow and causes an alteration in wind direction. When the wind strikes the windbreak it must move over and around the obstruction. This wind direction alteration creates a small area on the windward side of the windbreak and a larger area on its leeward side that is protected from the full force of the wind.

Windbreaks that are impenetrable to wind create a strong vacuum on their protected leeward side, which tends to suck the obstructed windstream into the protected zone. This reduces the level of leeward protection afforded by the windbreak.

Windbreaks that allow some wind penetration reduce the vacuum and consequently improve the windbreak's effectiveness.

In general, good windbreak plants have dense twigs and foliage with branches that form a thick growth even when bare of foliage. They need to have strong limbs. Pine, hemlock and arborvitae usually do well.

Q. I have a small greenhouse. It is new for me. Can I grow lettuce in it this winter, and what kind is best to try?

A. Indeed you can grow crisp and tasty lettuce on your greenhouse. Grand Rapids is a good loose-leaf variety, ready to eat 45 days after sowing seeds; Rudy is another good one, also 45 days; and Buttercrunch, 60 days.

Q. I get a nice crop of grapes, but when I put them in the refrigerator to keep them from spoiling, they don't taste good afterwards. Also, how can I keep my apples from going bad?

A. Grapes should not be stored with other fruits or vegetables because they tend to absorb odors that alter their flavor. They can absorb the flavors of rutabaga, onions, cabbage and almost every other fruit or vegetable. Apples should be stored at temperatures just above freezing, around 33 or 34 degrees.

Q. I picked some nearly ripe tomatoes, took them indoors and when they were fully ripe, put them in the refrigerator. A week later they were soft and practically no good. What was wrong?

A. Ripe tomatoes can be held for a short time at temperatures no lower than 50 degrees F. At lower temperatures, they usually break down and become soft after a few days.

Q. How much cold will broccoli and cauliflower tolerate?

A. Not much. Although they are cool-season crops, they will not tolerate temperatures much below 29 to 32 degrees. Unlike winter cabbage, they will be knocked out by a hard freeze.

Q. Is it possible to grow vegetables indoors during the winter.?

A. It is possible but very difficult. The major problem is lack of light -- short days and a lot of cloudy weather make it difficult for them to keep going.