IT'S HARD to believe that chopping up a small space increases its apparent size, just as it's hard to believe that repeated barriers to the sight will increase the sweep of a garden.

And hardest of all to believe (and most stoutly resisted by all proper gardeners, at least until it is forced on them) is the truism that luxuriance of plant growth in a garden is not a matter of fact, 0ut of contrast and illusion.

Another hard pill to take is the plain truth that architecture and her handmaidens of brick, stone, cut and dressed wood, masonry pools, all have a critical or even dominant influence on the garden.

Consider any courtyard, or a garden surrounded by houses or other buildings. There will be only a few minutes of the day, at noon, in which part of it is not in heavy shade. And this, no matter what the gardener's notions may be, will dictate much of the plant growth.

Nothing is more instructive to the gardener than to know a house well, and then visit the site when it has been razed. Or to measure his bedroom and then stake out that exact space in an open field.

When the site, or the measured dimensions of a room, are seen in an open field, anyone will say it is miniscule, and will strongly doubt that it can truly be the size of a room or a building.

It is only when walls go up, furniture intrudes, that the space begins to seem larger. It is exactly the same with a garden.

A cat-run piece of land, 40 by 120 feet, back of a house, will look small enough if it is open and grassy. It will seemingly triple in size if subdivided extensively with hedges, screens, fences, and furnished with terraces, pools, arbors, and so on.

As it happens, I do not know anybody who likes plants more than I do, or who has more reservations about architecture in general, or is more distrustful of stage sets, ornaments and gew-gaws.

Still, fact is fact. These things help. These are indispensable.

This does not mean -- needless to say, I hope -- that a forest, or a beautiful natural ravine, or a glade with a pond, or a sparkling stream, should be turned into a Disneyland with a heavy sprinkling of summer houses, sculpture, brick walks, fences, elaborate changes of grade level and so forth.

Often a woodland is best left alone, or subjected to a thinning of the trees, a tactful opening of views, and the introduction of some plants that accent its natural character. And it is easy to ruin a garden on the sea or a tidal river, when often the best thing is to accept with loud thanks the marsh grass, the sea oats, and whatever is there.

But you remember that emperor who was shown various sites for a garden at Agra in India. After some hours peering about, he said it was impossible to make any garden worthy of the name in such a wretched place, without a single natural advantage of site. It took him several days to get over this fit of despair and quietly choose a site after all.The cluster of gardens at Agra are rightly considered among the world's most beautiful, but they own everything to brains, to taste, and to marble and water tanks, not to nature.

An even more startling set of examples could be drawn from the gardens of Kashmir, where instead of flat muddy land steaming under an intolerable sun you have clear lakes, snowcapped mountains, sparkling air and a beautiful natural flora.

The sites there are natural gardens, and to those who lived on the Indian plains the entire vale seemed a paradise requiring nothing at all in the way of artifice to make it the ultimate garden.

But how much can be done, even with the best sites, may be seen in Kashmiri gardens. As usually, the gardens there have a rigid formal plan. A straight line (a stone-edged canal) down the middle, with few cross-lines, like a cross with a few extra arms. None of the ingenious shapes and curves you would expect in so wild a natural setting.

The water spreads out in formal pools, then is constricted to flow over man-made parapets to form falls, then is led out and led back and so on indefinitely. Marble pavilions straddle the water, over the falls, or flank its edges. The results for some centuries now have struck the world in general as unspeakably beautiful.

What was accomplished was (quite complexly) a tension of falling water and still water, massive foliage against plain surfaces, marble against peachtree bloom, and a balance rare in human affairs between rigid discipline and the most luxuriant love.

Back to our narrow cat-runs. Marble pavilions are rarely the right answer. But balance, tension, artifice, contrast, drama, simplicity of intent and complexity of detail -- these work as well in Anacostia or Georgetown as in Kashmir. Bulk, mass, light, water, gloss, plus the gardener's underlying passion for flowers, will always make a fine garden.

Now the visions of the poor brain do not always work out well in practice, as most gardeners promptly discover, and even the best and soundest ideas may take a while to come into flowers.

I sometimes think of the emperor at Agra, disgusted at the steamy muddy river and the featureless landscape, but committed to building a garden there anyway. During the years the construction was going on, the land graded, the massive earth-moving operations making even more mess than usual -- what sort of impatience, annoyance, despair he must have felt.

Even in Kashmir, the lapse between the final vision (and most gardeners have fitful glimpses first) and the first maturing of it may spread over many years. And even then, there may be only a few flawless times, when it is all perfect, balanced like a bird at the center of a tornado. The emperor, Babur, made his greatest (to him, at least) garden at Kabul, which one thinks of as utterly godforsaken and impossible.

Those were the days, he jotted down in his memoirs, of the garden's beauty. He had made the garden years before, and now, after a long time, he saw it once again. It was, miracle of miracles, as glorious as he had meant it to be. Then he left again, observing (with the restraint of a gardener) that the one time he ever saw it perfect was on that visit. Not surprisingly, he took elaborate care to see he was buried in that (to us) wilderness which (to him) was all he ever knew or dreamed a garden might be.