SUPPOSE you have a garden, 25 by 40 feet, in back of the house; and at the far end, and on both sides, you have admirable neighbors who are not, however, much to look at.

But suppose there is an existing set of fences, both low and dismal to look at, and you wonder how to achieve that bowered privacy that gardeners seem to think so highly of.

In a garden 25 feet wide there is not much point planting cedars and cypresses as screens, and a thick shrub border of viburnums and hollies and so on is no answer in so small a place.

Neither is it much help to suggest (as heartless garden writers do) a seven-foot wall. But here is how to proceed, making do with life as you find it:

First, the waist- or chest-high fence can be covered with vines. They need not be all the same entire perimeter of the garden.

There may be (there ought to be) a place to sit, the size of a small living room, at least, and this may well be glorified by four-by-four wood posts supporting rafters on which a grape vine is grown. Very well, from that vantage point look at your boundaries and you will see that one seven-foot mass of foliage may do wonders in blocking out your otherwise excellent view of your neighbor's garbage can, etc.

Such a rose as 'Blossomtime' can be grown as a free-standing shrub, a six- to eight-foot rose, as perpetually flowering as any I can think of (and far more than most) with flowers of flawless shape and texture, a remarkable scent and a trouble-free physical constitution.

Other stretches of the fence could be covered with the dense-growing Japanese autumn clematis (blooming at Labor Day) or the common Irish ivy or what you will; but the point is to make the fence a background of green, even if it is only 40 inches high.

Again, from your vantage point, see how little is needed.

Maybe another shrub or two, but think twice before you choose forsythias or other shrubs with uninteresting leaves. Maybe an upright narrow conifer, a narrow form of yew or juniper would do. Maybe Beale's mahonia or a holly of moderate narrow growth.

Now you have a low border of background green from the vines and at strategic points a taller bulkier plant -- only two or three, perhaps along the entire perimeter -- and an open center.

Inside the fence, maybe four feet inside, maybe less, you might erect wood posts nine-feet high (a 12-foot post sunk three feet in the ground and it is best to use lumber treated against decay). These could be spaced a few feet apart, perhaps three or four posts on each long side of the garden and connected by chains or ropes at the top.

Sometimes I think black is the best color for such things, since white is flashy and compels instant attention from the eye. Two of the posts could be planted with roses of moderate growth like the climbing 'Golden Showers,' but I would not overdo the roses since the rose plant itself is not very ornamental. Maybe one on each side would be plenty.

The native trumpet vine or one of its garden forms could be grown up one of the posts and trained along the ropes. Or grape vines. Or any wisteria. Any number of large-flowered clematis would do for any of the posts; but to cover the connecting chains or ropes (if that's your idea) you need a vine of great vigor, among which are not only the trumpet vine and wisteria, but the fleece vine (Polygonum aubertii) with white late-summer plumes of flowers, or the Virginia creeper from our native woods or the half-evergreen Japanese five-leaf akebia.

It may easily be the case that you do not want or need a permanent climber on part of the ropes or chains, but would like something rather luxuriant on them (or along part of them) in the summer. The tropical moonflower vine, as easily grown from seed as a morning glory, will answer; and if this is the choice, then I would start the seed in a pot (one seed to a pot) in late March or April, not planting it at the foot of its post until mid-May.

I think you will find, viewing from your sitting place or arbor, that even the low fence of greenery, plus the posts with swags of vines, will give you an admirable sense of enclosure without blocking out all the light and air, or overwhelming the small garden with too-massive shrubs, or disturbing the character of the neighborhood with a high solid barrier.

In the center, which has been kept open, you should consider a fish pool in the sunniest spot, preferably right beside the place where you sit.

Or one generous-sized bed platned solid with roses or whatever your favorite flowers are -- maybe nothing more rare or startling than zinnias. These, by the way, need not be a grand mixture of every color known to man. They could be white and canary-colored zinnias, or all lavender, or all scarlet, or what you will. You may like the effect of all colors mixed up, but you should be aware that other effects are possible.

Or the great central bed could be planted with tulips, peonies, irises, daylilies, phlox, chrysanthemums, filled in here and there with nasturtiums and petunias or the like.

My own inclination, in such a piece of land, would be to grow masses of daffodils against the fence with occasional clumps of daylilies, maybe four big clumps along each of the garden's long sides. You will probably discover that the light yellows show up better than the others.

If you sit in the garden at night, the wild Hemerocallis citrina is as useful as it is beautiful, commencing about July 10 with all slender stems crowned with many almost tubular trumplet lemon-yellow blooms that close before noon but open all night. It is strongly fragrant, too.

There are people, needless to say, who prefer in daylilies (as in other flowers) the thickest, fattest, flashiest blooms that can be acquired, and their darling is more likely to be the somewhat gross 'Mary Todd' than H. citrina. Of course you could have both.

But suppose the garden is too shady for peonies and roses and irises? The borders along the fence might still be full of daffodils and other bulbs that bloom before the leaves are out, and the central bed could be given to azaleas, andromedas, Spanish scillas, Virginia bluebells, barrenworts and the dozens of other pleasant creatures that make do in woodlands.

On the posts, instead of roses and trumpet vines, there are akebias and Carolina jasmines and clematis and honeysuckles to be thought of.

If there is no sunny spot for the fish pool, then put it in a shady spot. The yellow water lily 'Chromatella' stands about as much shade as any, and even if it blooms poorly or not at all in the shade, its leaves are beautiful. The open shaded water will show off the brilliant goldfish all the better; but in shade you must not expect water lilies to flower.

In a large garden the background would be provided by noble trees, and in a medium garden by screens of holly and juniper and so on.

But in our very small garden, we have merely greened the fence and acheived height with wood poles and vines, and we are none the worse for this poverty of space. If total delight is possible in 25-by-40 feet, we are fools to dream of half-acres, which can provide more plants, of course, but hardly greater pleasure.