A great idea for Monticello, Thomas Jefferson's ingenious and pretty house at Charlottesville, is announced today -- the establishment of a national Historic Plant Center to preserve and distribute old garden plants now out of commerce or at least rather hard to find.

It should be very agreeable to many gardeners to be able to buy 'Marseilles' figs and 'Calville Blanc' apples and 'Carnation' cherry, propagated at Monticello.

These varieties, among many others that will eventually be offered, were favorites of Jefferson who said of the fig that it was "the finest fig I have ever tasted." Of the cherry, Jefferson said "no other type deserves the name cherry."

Before racing down to Charlottesville, however, you should know sales will begin probably in the fall of 1987. You might also keep in mind that Jefferson was a generous man, sometimes extremely enthusiastic. Jefferson said of the so-called 'Taliaferro' apple that it was the "juiciest I ever tasted," but efforts to locate this old variety have been unavailing.

Probably an apple of great distinction would not have died out completely, and my guess is that (Jefferson notwithstanding) if it is ever discovered it will not be quite the worldbeater Jefferson said.

As for the fig, a fully ripe fig of any commercial variety is likely to seem miraculous, and 45 years ago (before the place became quite the tourist attraction it is now) I used to swipe figs from the bushes at Monticello occasionally and do not recall anything very special about them.

But then you take the 'Newtown Pippin' apple, one of the varieties that will be sold. This was always called the 'Albemarle Pippin' in Virginia, though now it is considered identical with the 'Newtown,' an 18th-century Yankee variety. It is certainly a superior apple, and you might think it would have remained in heavy commercial production, but it has not.

They still grow it here and there, and sometimes I have made trips to Charlottesville in October to buy it. It is also available from some commercial nursery sources. But I think you could say it is a bypassed apple variety, and hardly a significant occupant of modern apple orchards. I think its yield per acre may suffer in comparison with some other apples, and I know for a fact that women (chief purchasers of apples at the grocery) do not find it pretty to look at. It is almost colorless, sometimes greenish or flushed yellowish, and a bit lopsided.

What chance has such an apple to compete with gorgeously shaped and colored apples like 'Delicious,' which can be a good apple, but as usually encountered is mealy and which depends more on its sugar than its flavor. The old pippin is a far superior apple, but it has not been able to maintain a place at the grocery store where it will be passed over.

There is nothing remarkable in this. Many old books are vastly superior in quality to many new ones, but if you're in the business of selling books you better stock the current stuff, even when it is junk.

I remember a conversation with Henry Harpur Crewe, who lent the amazing bed draperies at the "Treasure Houses of Britain" show at the National Gallery. Gardeners know the name from a wallflower, so I ventured that this gentleman grew quantities of 'Harpur Crewe.'

Not at all, he said. He had one plant of it, which he had acquired after some bother. This old wallflower has remained in cultivation, but not in the general nursery trade, so Harpur Crewe had some looking about to do before he found it.

Same way with the 'Newtown Pippin.' It has always been available, but you had to plow through a good many nursery lists before finding a nursery that sold it.

And as for the 'Carnation' cherry and 'Calville Blanc' apple, I never even heard of them, yet they might both be quite superior dessert fruits, better than many that are more widely grown today.

There are also many varieties of English daisy, primrose, pink and so forth that are very hard to find in nursery lists but which a lot of gardeners might enjoy growing, so it is good news that many uncommon varieties of these perennials will eventually be sold at Monticello.

I am a great believer in richness of variety, in flowers, trees, vegetables, bamboos and everything else. "Let a Thousand Flowers Bloom" is one of the few things I ever agreed with Chairman Mao about.

In quite recent years the American corn crop was decimated by disease, but through a miracle of energy and enterprise, American breeders so quickly introduced resistant corns that the public at large was unaware how grave the crisis was.

And I well remember the amazing cotton station at Starkville, Miss., where hundreds of varieties of cotton are grown each year, merely to keep the strains alive. There are cottons with green fiber, red fiber, and so forth, of no immediate commercial interest, but possessed of genes different from all other cottons, and someday they may be called on in a breeding program. If they die out, their genes will of course be lost; and as in corn or potatoes or any other plant (or animal, including humans) safety for the species is enhanced by the widest possible genetic variation among individuals.sk

But even apart from genetic value, I like the idea of keeping old varieties alive in gardens, simply because they are interesting in themselves and often beautiful in some particular way. One year I lost my bulbs of the wild Scilla autumnalis, a very modest lavender scilla that blooms in September and October. I have seen it growing in the rotted stone atop of a magnificent Roman ruin, the Pont du Gard, in southern France. You could pass by it in full bloom and hardly notice it, but when I lost my clump I was very sorry. Some day I must exert myself to find new bulbs. So there are many plants like this that have lost out against flashy roses and dahlias, but which gardeners treasure; and many more would treasure them if they knew them and knew where to buy them.

There is still another value to displaying and selling old varieties at Monticello, and that is the pleasure of seeing things new to you, things Jefferson grew and loved (and others he would have liked if he had known about them). It is not necessary to want to grow them oneself, or to want to breed from them.

The only furniture at Monticello I ever would like to possess are the big plain mirrors of the saloon, or salon as they probably now call it. I once measured them with the idea of having some made, decades ago, but of course never got round to it. The other stuff, which I would not want, I nevertheless like to see. Life is too short to be interested only in things one can use oneself. Life is made bright and sparkly by all manner of things (and people) one would not necessarily want for supper.

The new director of this new center is John Thomas Fitzpatrick, who was a research horticulturist for four years at the well-known nursery White Flower Farm, and who earlier worked as garden curator for Alan Bloom at Bressingham Gardens.