RENE DUBOS, the microbiologist, is one of those ameliorative, conscientious Frenchmen -- like Jean Mayer, the nutritionist, and Jacques Cousteau, the oceanographer -- who, even since the days of Crevecoeur and de Tocqueville, have been showing up in America quite regularly to try to reassure us or help to set things right. Together, they contradict our frequent opinion of the French as being despairing like Gide, solipsistic like Sartre, morbid and cynical like Genet or nationalist to the point of self-obsession like de Gaulle.

Dubos is turning 80 now, with a lifetime's reading in literature and the sciences behind him and world-wide, firsthand memories of environmental developments in China, Ethiopia, the Netherlands and so on. He has special grandeur in summarizing the large body of knowledge that elderly people can sometimes command -- and he is not after honors here. Rather, The Wooing of Earth , with its hopeful title (borrowed from Rabindranath Tagore), seems more in the category of a parting gift of optimism than would a book written in the ambition and vigor of mid-career.

Dubos, raised in the lovely Ile de France region close to Paris, never saw a wilderness till he was 27 and visited New Mexico. Accordingly, his vision of a planet already "humanized" by many centuries of manicuring by a devoted peasantry, European and Oriental, is different from what most Americans understand. From bare Greek landscape to New England farmstead, he says that human activities have created the scenery we most love. Even denuding has its place: "Would logic have flourished if Greece had remained covered with an opague tangle of trees?" Because life has created further life on earth, building upon itself consecutively over the millennia, as simpler forms prepared the way for more complex organisms, he suggests that man needn't be content to seek merely a modus vivendi with his biological environment, but can hope to improve upon it, continuing the process of creation -- and points to the example of Hawaii, an island with a more diverse and interesting flora since Westerners arrived

One of Dubo's impressive qualities is that he can put forth a brief for those who disagree with him. He knows all of the alarming statistics about desertification, the filthying of the oceans, the razing of the world's rain forests at a rate of 50 acres per minute that threatens the climate we live in and the very air we breathe. He knows that even in the "wilderness" of Yosemite Valley on a summer weekend there are 8,000 people per square mile; that 25,000 people climb Mount Fuji in a day; that every hour 8,500 more people are born than die. He doesn't discount, then, the possibility of a vast and bitter famine, a nuclear holocaust, or disastrous alteration of the atmosphere.

He speaks instead of the fact that "natural ecosystems are characterized not by high productivity but by resilience and flexibility." The island of Krakatoa, which blew up in a volcanic explosion in 1883, was again host to 300 plant and 300 animal species, including crocodiles and pythons, within 40 years. In 1855, only eels survived in parts of the Thames estuary, but now there are 83 fish species, among them salmon. The Brooklyn Botanical Garden was built on an ash heap; the forests of Verdun have nearly restored themselves to their original state. We humans, too, as he points out, carry dormant in use the capacity to adapt almost immediately to primeval or "Stone Age" conditions, as the voyageurs and coureurs de bois did in America 200 years ago. Indeed, city people, by jogging, sailing, gardening and going into the woods to walk or fish, try to recapture as best they can the sensations of their recent past.

Still, Dubos interrupts the flow of his book occasionally to argue with disconcerting querulusness against reviewers who have disputed his optimism, or who may harbor more enthusiasm for wild things. He has the odd idea, for instance, that it was the Plains Indians who decimated the buffalo -- not official Army policy to kill the buffalo to starve the Indians. He misstates Thoreau's reaction to the Maine woods; pokes mild fun at Emerson for not roughing it in the High Sierras the way John Muir did (which is like taking a minister to task for not having become a monk); and in one of several uncharacteristic misrepresentations of natural history, blames beavers for drowning forestland, when of course it is the beavers who break up the forest into the woodland glades he admires.

He makes the point that fossil fuels result from nature's failure to recycle organic material; that half of the earth's 8 billion acres of potentially arable land is not being tilled because of a lack of soil nutrients that could be shifted around. He hopes, however, not just for effective management of such vast matters, but that mankind's sense of noblesse oblige will persuade us to make a strong effort to preserve the earth's infinite biological variety. Even at best -- if world-scale famine and holocaust do not intervene -- this shining ideal may seem a bit Panglossian to those who think democracy does not stick close to Thomas Jefferson's model for long, but turns either to an egalitarianism of the lowest common denominator or to some kind of dictatorship with a regimentation equally leveling to nature and man.

Think globally but act locally, says Dubos, believing that global planning can be accomplished without totalitarianism (or that benign totalitarianism can remain benign) and that regional distinctions can be maintained without the nationalism that causes wars. Remembering his boyhood in a deliciously regional peasant-farmer society where people traveled on horseback or simply walked, in close contact with the perfume of flowers and the songs of birds, he hopes that such an intimate association will survive in an industrial or postindustrial world where only 4-percent of the population may be engaged in agriculture. Perhaps these frail, honorable hopes would be more convincing if they came from a thinker of somewhat darker imagination -- a man less a favorite of the clergy than Dubos is, but instead with a hint of Sartre and Genet spicing his reflections.

We began as creatures of the savanna, not the forest, and just as our vegetable foods are sungrown, as would befit life on the savanna, so are our pleasure places landscaped to have trees spaced about in savanna style. However different from a wilderness our parks have become in the uses that we put them to, we still seek both a leafy Stone Age refuge and a "view," where, like hunter-warriors, we can look out over a wide area without ourselves being conspicuous. We feel guilty and incomplete, Dubos says, when we lose touch in a Nature which is by every definition our mother. Although agriculture itself has now become "nature" to us, as we have lost our old holistic awareness of the broader, truer progression of Nature, we must, Dubos says, preserve some wilderness "in which to experience mysteries transcending daily life and from which to recapture, in a Proustian kind of remembrance, the awareness of the cosmic forces that have shaped humankind. . . . The wooing of the Earth will have a lastingly successful outcome only if we create conditions in which both humankind and the Earth retain the essence of their wildness. The symbiosis between these two different but complementary expressions of wildness will constantly engender unexpected values and new hopes, in an endless process of evolutionary creation."