As agreeable as any small public garden I have ever seen, and far handsomer than most, is the Enid A. Haupt garden of the Smithsonian Institution, and if any gardener has not yet seen it, he should put this on a list of things to do.

A few years ago I wrote a somewhat harsh piece about a "Victorian garden" planted on this same space, and I said it was unworthy of the institution and blah, blah, blah.

The new garden, dedicated last May, is also a Victorian garden, but what a difference. What a difference a ton of money makes. The earlier garden, which was only a temporary planting (for the entire area was going to be excavated for underground museums) was a low-budget operation, and there were many good reasons why it was not impressive. My main objection to it was simply that it was hideous.

But the new garden, totally Victorian, shows that any style garden can be splendid when masterfully designed and planted.

Here the centerpiece is a series of ribbon borders in green and yellow set against grass. When done with taste, such exercises can be pretty to see. And the garden is full of antique benches and urns and objects on which to rest both the rump and the eye.

Horticultural director James Buckler has stuffed the place with flowers and things in great tubs -- a notable cycad at the entrance, some superb red-ribbed bananas in modern square metal tubs painted black.

The old stone entrance piers have huge boxes set atop them, overflowing with rose-colored verbenas and geraniums. The maintenance of the garden is flawless, and the total effect unparalleled in any public planting in the capital.

The garden can be entered from the Mall (between the old Castle and Arts and Industries buildings on Jefferson Drive) or by going through the Castle itself and out the back door into the garden, or through gates just east of the Castle, or through the ceremonial stone-piered iron gates on Independence Avenue.

Beneath the garden are the two new museums, the National Museum of African Art and the Arthur M. Sackler Gallery, specializing in Chinese art but also including art of Persia and India.

Once these museums were finished (they open to the public Sept. 28) the earth was put back on top of them and the garden planted. The garden looks fully established, as if it had been there for years, and I consider it one of the greatest of all attractions in the capital, that no tourist should miss.

But I was sorry to see the century-old linden tree, the only large tree in the garden, is in a weakened condition. It may die. Its leaves are much smaller this summer than is normal, and some splitting of the bark has been noticed near the ground.

The tree is not only old and large, but uncommonly beautiful, as it branches low to the ground in a way unusual for lindens.

From the beginning this tree had a high priority for preservation. At one point a plan was devised to build a cylinder of concrete, extending 60 feet below ground level, to protect its roots, but Buckler said this scheme, which would have cost perhaps $800,000, was abandoned.

Instead, he said, a considerable area around the tree was fenced off, to keep trucks and construction equipment from compacting the earth. Also a watering system was installed, and steel cables installed to ease strain on the main branches. (Altogether about $9,000 has been spent in caring for the tree, Buckler said).

There was a time when cars parked in what is now the garden. You could park your car right up against the trunk of the linden. Stress to old trees can be cumulative, and possibly we are now paying a price from the parking-lot days. And this past summer has been hotter and drier than usual, adding to the stress.

The underground museums form a large rectangle, but to keep from disturbing the old linden, the floor plan was reduced by slicing a triangle out of the northeastern end of the rectangle. Thus the museums do not extend beneath the tree itself, and its roots can still go down to China, as you might say.

If the tree should die, within the next two or three years, it will be a loss to the garden, of course, but at least all reasonable efforts were made (even to the extent of altering the museum building design) to save it. And other trees are coming on.

Elsewhere in the city the crape myrtles are blooming. Several gardeners, doubtless from the north, have asked what they are. These are deciduous shrubs, sometimes the size of a small tree, with panicles of flower in watermelon red, other tints between red and white, as well as several tints of lavender, down to a fairly decided purple. The individual florets are crinkled. A large old bush covered with bloom, like great spikes of phlox, is a beautiful sight, and the shrubs bloom for some weeks, starting in July and ending in October, when the foliage begins to turn orange and other colors.

Several have also asked what the shrubs are that seem to be covered with snowballs, rather like the spring-blooming viburnums that produce snowballs for kids to have battles with. The ones blooming now are a different genus, Hydrangea. The huge fat snowballs are simply white varieties of the so-called "hortensia" hydrangeas. The others, whose flowers are not globular but somewhat triangular in outline, yet still suggesting snowballs, are Hydrangea paniculata in its several forms