My first autumn day in Washington, I emerged from my cave-like Capitol Hill apartment braced for end-of-summer humidity, seasoned with fumes from I-395 and steam from a nearby power plant.

What greeted me instead was a world transformed: a clear blue sky haloing a blindingly crisp grove of trees in Garfield Park. And in my little courtyard, as I wondered where all the hot, wet, white air went, a small breeze hit me square in the face. There would be life after summer.

What followed were three of the most pleasant months I'd ever known. The procession of maples, ashes, oaks and dogwoods framing marble monuments made me wonder how spring had managed to corner the seasonal cliches in Washington.

Could any of its offerings compare with golden ginkgo leaves shimmering in the lamplight, or the brilliant collage of Japanese maple leaves peeking through the first light blanket of snow?

I grew up in Vermont with its short-lived but gorgeous explosion of autumn color. For ten days in October the world pours into the Green Mountain valleys to glimpse the crimson and gold hillsides against the ice-white birches and deep-green conifers.

I am also a veteran of one -- and only one -- fall weekend on Skyline Drive.

Here, autumn's most outstanding feature is its length: from equinox to solstice, the air crisp and clean, the days mild even into December, the trees a steady flow of color.

Autumn in Washington itself is much more dramatic than in the surrounding countryside: Because fall, at its best, is a season of bold contrasts, our nearby woodlands, largely gray-limbed and deciduous, can't compete, but Washington's white memorials provide a contrast every bit as striking as the white birches of the north. The city is also replete with evergreens, including shiny-leaved magnolias, which ably balance the sparkling stone. Also, although our native maples rarely equal the vivid colors common in New England, some of the Japanese maples planted here turn as bold a red as any tree in Stowe.

As the days grow shorter, there's less chlorophyll -- the green pigment -- in the leaves and as the last of the chlorophyll breaks down, other pigments, singly or combined, dominate. Yellow hues are produced by carotenoids, the same pigment found in daffodils, corn and egg yolks. Scarlet and purple come from anthocyanins, also found in cranberries and grapes. Warm days and cool (but not freezing) nights are best for producing brilliant anthocyanins.

Washington harbors an unusually diverse collection of native and foreign woody plants -- more than 300 species of trees and large shrubs by my count -- creating not only our famous flowering spring but also a long and colorful foliage season.

A curious and pleasing side-effect of this mix is that the leaves, in effect, turn in shifts. In mid- to late October, most of the native American species (sugar and black maples, American beeches, American elm, ashes, dogwoods, hickories and some oaks) are at their peak. Then, a trip through Rock Creek Park can be as rewarding as a mountain hike. The towpath, Theodore Roosevelt Island, the National Arboretum's Fern Valley and parks throughout the area are colorful places to visit when native trees are at their peak.

In November, when most native trees are already bare, such exotics as the ginkgo, Japanese maple, Bradford pear and European beech reach their peaks. The colors of the ginkgo and Japanese maple are particularly outstanding, and with half the city's trees already stripped of foliage, sweeping views lost in the leaves all summer are suddenly visible again.

That's when urban and suburban neighborhoods and smaller parks, with their concentration of exotic trees, are good places for local color. The Capitol grounds, National Zoo, Soldiers' Home, Walter Reed Army Medical Center and area cemeteries all have balanced collections of native and exotic trees, yielding colorful foliage for several weeks.

The view from the hill atop Arlington Cemetery, in front of the Custis-Lee Mansion (Arlington House) is breathtaking from mid-October through mid-November. The Capitol is another excellent place for lasting color coupled with dramatic views.

The symmetrical beauty of the American elm, its elegant profile so aptly suited to the Washington scene, can still (knock on wood) be seen in many stands; those on and near the Mall, particularly, are poignant reminders of the elm- lined streets of yore. Dutch elm disease has brought down many in other parts of town, but the effort to protect survivors goes on.

Autumn may be the best time to identify the many trees that have been brought here from Europe, Asia, Africa and the expanses of this continent. It's like detective work: The more clues you find, the more easily you will crack your case. In the fall, more arboreal clues are available. You can examine the leaf before and after it has turned. Winter buds are plainly visible. Most significantly, many trees bear fruit in autumn.

Oaks, buckeyes and horse-chestnuts, trees of the pea family (locusts, Kentucky coffee-tree, pagoda tree, yellow- wood), catalpas, paulownia and many other trees commonly planted in the city are easier to identify in autumn, when you can compare leaves and mature fruit. On a crisp autumn day, rooting around for fall fruit and colored leaves can be one of the most enjoyable experiences going.

You may want to start a collection of pressed leaves and fruit (a herbarium) for future reference or art projects. Simply press leaves between pieces of newspaper, recording the date and place of collection, with the name of the tree, if you've been able to identify it, on the newspaper. Then press the folded paper under a stack of books, piling up as many specimens as you'd like. Fruit can be tagged with the same information and stored in egg cartons. If you have been unable to identify a certain tree, visit it again in the spring or summer when it's in bloom and collect the flowers, which can also be pressed. With fruit, leaf and flower in hand, you should be able to tell what it is.

For anyone wishing to take up landscape photography, now's the time. While endless photos of green trees in summer get boring rather quickly, a warmly dressed photographer who goes out among the city's trees and monuments on a clear autumn day is bound to be heartened by the results. If all else fails, there's always the ginkgo tree. Its golden, fan-shaped leaves will take the picture for you!

The key to savoring fall is to pay close attention to the changing scene. Visit the same spot several times during the season, if you can, or establish a tree-lined running or biking route. Don't let wind or rain keep you indoors; briskly blowing leaves and long, moody rain showers are important ingredients of the autumn ambience.

ON THE TRAIL OF THE TREES Following are the locations of some outstanding examples of Washington's more unusual and/or spectacular trees:

GINKGO -- Arlington Cemetery, on the hill in front of the Custis-Lee Mansion (Arlington House) and on the Capitol grounds.

DAWN REDWOODS -- National Arboretum (the needles of this rare Asian conifer are deciduous and turn bright bronze in autumn).

KATSURA -- Mammoth tree on the right just inside the main entrance to the Dumbarton Oaks garden.

AMERICAN ELMS -- On the Mall and between the Mall and the Potomac.

CHINESE ELM -- This unusual fall-blooming and fruiting tree has been planted as a street tree in several places in Washington. A gorgeous specimen is on the Library of Congress grounds.

EUROPEAN BEECHES -- (including the copper-beech form); Smithsonian Museum of Natural History, along the river between the Lincoln Memorial and the Kennedy Center (gorgeous in late fall) and in Rock Creek Cemetery.

WILLOW OAKS -- The Capitol grounds (southeast section).

KENTUCKY COFFEE-TREES -- Capitol grounds, southwest section (large pods visible fcrom autumn through winter).

SUGAR MAPLES -- Capitol grounds.

JAPANESE MAPLES -- Capitol and Library of Congress grounds.