I went outside this morning to pick a spot in our small urban landscape for a new elm tree. This is serious business, choosing the proper place for a newcomer. It won't do to plant a tree too close to the house. I have to be sure it won't block the sun from my vegetable garden or infiltrate the perennial bed.

My planning is wildly premature. My tree is only six inches tall, barely a treelet. If it grows a foot a year, as predicted, it will still be six years before the elm reaches my height; 30 years before any tan is ruined. It is an act of hubris and hope to worry about such things as shade when the twig is just six-inches tall. But that is the essence of tree planting: hubris and hope.

Today is one of those last, fragile, warm days of fall that seem to suggest a leap of faith. In this barren season between leaves and snow, we plant the last bulbs genetically programmed for spring, put the last tree in the ground- one step ahead of the frost.

This year, my task has a wonderful, even corny, edge of optimism to it. Once my entire street, like thousands of others, boasted the elegance of a dozen American elms that reached as high as three story buildings. But 20 years ago, one by one, they were destroyed by Dutch elm disease.

The blight left the brick skin of this neighborhood raw, and stripped the sidewalks naked to the sun. The elms were later replaced by Norwegian maples, which are lovely but which are not American elms.

So, when I find the proper spot, there will be an elm again on my street. An American Liberty elm, grown, tested and warranted to resist the disease that has killed 35 million of its kind.

I didn't come by this tree easily. I went on a kind of mission to the source, the Elm Research Institute. I drove up to Harrisville, N.H., on one of those dismal days that come at the end of a warm November, in and out of pockets of fog on mountain roads.

The town of Harrisville was in every way pure New England, a mixture of centuries, the old and picturesque, the new and technological. The Elm Research Institute was located on the bottom floor of a renovated 19th-century brick mill: a historic restoration project housing a natural restoration project.

The institute exists because one man, John Hansel, watched the elms outside his Connecticut home die. That was what you did for the elms in the Sixties. You watched them die. But Hansel was different; he started ERI with money from private citizens and foundations.

Today this modest nonprofit institute operates a program to save some of the standing elms, at least those trees of historic dimensions. On the ERI's pine- paneled wall is a map full of pins, each one representing a town with a Conscientious Injector, some person or group committed to saving the elms from Dutch elm disease by injecting them annually with a powerful and effective fungicide developed nine years ago. About 185 Conscientious Injector groups from Baudette, Minn., to Macon, Ga., to Denver, Colo., have volunteered to inject about 8,000 of the millions of remaining elms.

For those people and places that have already lost their elms, the ERI has what they forgivably called the Johnny Elmseed program. This year, for the first time, they distributed to their members about 4,000 genetic clones of disease-resistant elms that were developed in Wisconsin and raised in New Hampshire.

Mine was one of these elms, plucked out of the misty mill room that doubles as the greenhouse. It came with a green card that bears a computer number and planting instructions and no promises. I am told that even Dr. Eugene Smalley, who cloned this tree, is not sure what it will look like. It may be majestic, he has said, or, "It may turn out to be a ratty dog. We won't know the answer for 20 years."

But today I have no concern about its beauty. When acid rain threatens the sugar maple and fungus threatens the chestnut tree and people threaten each other, there is something wonderful in being part of a comeback story.

What I am worrying about is whether my tree will get tangled in the telephone wires and whether its trunk will upend the cement sidewalk. Anyone who plants a tree knows how to hope.