If you go there from Manhattan by car, you drive past some of the most desolate urban landscape in the country, the fire-gutted, poverty-ravaged South Bronx. That makes your destination seem all the more implausible when you get there: 250 acres of botanical garden right in the middle of the Bronx, complete with a newly restored turn-of-the-century glass house that itself covers very nearly an acre of land and features a vaulting 90-foot-high central dome through which the sun pours down on a grove of palms.

A compulsive gardener will OD on the place - the rock gardens, the wildflowers, the hemlock forest, the tropical and subtropical orchids, the roses and lilies and "skywalk" looking down on giant ferns. But there is more. The restoration of the New York Botanical Garden and its great glass conservatory is as humbling as it is cheering. That is because so much of the demage that had to be repaired was deliberately wrought by people who thought they were doing the Lord's work. Here one encounters the abiding, if depressing, truth that underlies so much of the historical preservation and reclamation that is now going forward in American cities: The most you can hope for, it seems, is that the destruction rendered in the name of one generation's assumptions and taste will not be beyond redemption by another.

In fact, a lot of social history is crammed into the 87-year lifetime of the garden. Its founding reads like something out of E.L. Doctorow's novel "Ragtime" - J.P. Morgan and Andrew Carnegie and Cornelius Vanderbilt sitting on the original board of managers, and arranging to have a special railway stop at the garden entrance. And from there to 1975 and the vicissitudes of Abe Beame, when the city had to renege on its pledge to finance a large hunk of the garden's restoration, the saga has closely mirrored the changing values and fortunes of the city.

Two phenomena stand out. One is the general decline of interest in the place in the years following World War II. The other is the well-intentioned disfiguration of the great glass house by modernizers, starting in the 1930s and resumed in the 1950s. "World of Tomorrow," read the proud and misguided 1939 New York World's Fair slogan under which exquisite filigree and other ornamentation was stripped from the conservatory, recreating it as a kind of bastardized, apologetic part-Victorian, part-modernistic structure. The philanthropist and editor (and passionate gardener) Enid Haupt picked up the $5-million tab for the the restoration of the conservatory and its courtyard; and the building is now fittingly named for her. But she and everyone else concerned readily and sorrowfully concede that there are limits to what could be done, that some part of the loss was beyond repair.

So much for the confidence with which Robert Moses and other tastemakers of the 1939 World's Fair viewed "Tomorrow." They were no more able to foresee the way we would look at such a building and feel about it today than were the postwar municipal officials who let the whole institution slide to the edge of ruin. In fact, by the beginning of this decade the conservatory was run down to the point of becoming unsafe, and a decision had to be made either to restore it or to raze it. It was at at this point that some friends of the conservatory suceeded in getting it designated a historic landmark in New York - which was a critical moment in the rescue of the enterprise as a whole.

Since that time there has been an exuberant growth of interest in the garden and of municipal and community involvement. Why? In part, this too reflects a change in perceptions and values and tastes that has seen a growing national preoccupation with green things, with the preservation of at least a little chlorophyll amidst the all-enveloping haze of auto fumes. Dr. Howard S. Irwin Jr., a botanist by training who is president of the garden and who lives in a cottage on the grounds finds this only natural. "After all," he says, "we were originally forest creatures and savanna creatures and then we went on from there." But he does not confine his explanation of the garden's renewed popularity to some benign, if atavistic, response to urbanization. He speaks of the revitalization that has come from the heightened 1960s bred perception of the importance of a community connection for the garden - a revitalization that has resulted from opening it up in new ways to the people who live around it.

We are not talking here about latter-day J.P. Morgans and Cornelius Vanderbilts and Andrew Carnegies. We are talking about schoolchildren who are bused in for classes and exploration and play, about teen-age ghetto kids on government grants learning a horticultural trade that has evidently been an enormous success, about old people who treasure the garden as a safe and revered park and about thousands of visitors who use the grounds for picnics, parties and strolls - and some even for weddings, which are a hallowed tradition of this garden.

The garden's literature boasts of a "please touch" policy in the children's area, where New York small fry who arrive believing that spaghetti is "the stem of a plant that grows in Italy" are encouraged to plunge in and look and feel and taste - and learn. Irwin says that one of the more poignant scenes you can witness on Sundays is that of poor, young urban kids bringing their parents to the conservatory to observe the evidence of their weekday gardening adventures. What is so poignant, he says, is the spectacle of the parents, themselves obviously unschooled in the wonders of nature and absolutely transfixed by what the children are showing them - all the while, however, trying not to betray that they are far less knowledgeable than their kids.

It's when you think what a close call all this had with the boredom and bad taste of another time that you realize how much there is to cheer and also to be humble about in the restoration. The same emotions are no doubt appropriate to narrowly won restorations of other cities' great landmarks and structures. But I think they are especially appropriate to anything to do with gardening, as any gardener - at all times half-elated and half-destroyed by nature's ways - will tell you.

I suppose I have to concede that our own values and way of looking at things are as chancy and subject to reappraisal as were those of the garden's near wreckers. But I'm damned if I'm going to. One ends up arrogant and self-certain after all. I can't imagine the revisionism that will fault the opening up of these fragrant acres to a new life in the community, and I think the joy people are taking in the revived garden and glass house will be as timeless and indestructible as the beauty of roses.