If there's any place where people have done something about the weather besides complain, it's here. The something done is planting trees. Architects and landscapers, professional and amateur, have long realized that Washington's near-tropical summers, long autumns and springs and cold-but-thaw-filled winters support a wide variety of native trees and also encourage an abundance of imports to adapt and thrive.

Everywhere you go in the area you notice lots of trees, especially at this time of year when they are flaming into fall color. And lots of kinds of trees, which is exactly what Washington and Jefferson had in mind when they planned the new capital that was to rise from the swamp. Both were tree enthusiasts and experimented with establishing exotic varieties at Mount Vernon and Monticello.

Jefferson oversaw tree plantings when he was in the White House and other presidents carried on the tradition, notably John Quincy Adams and Andrew Jackson. But the roots of today's many-splendored forest were planted mainly at the turn of the century, when Frederick Law Olmsted designed the Capitol grounds and the Department of Agriculture established the Forest Service and began experimenting with seedlings from all over the world. Many Forest Service employes took work home with them and new species began sprouting all around town, especially in what were then suburbs -- Cleveland Park, Chevy Chase, Takoma Park, Brookland.

Flourishing today in those areas are full-grown varieties of trees found nowhere else in the hemisphere. On Connecticut Avenue just inside the Beltway there's a huge white oak that is the only full-grown Quercus variablis in the country. It was planted around 1912 by David Fairchild, a stalwart of the Forest Service.

Most of the big umbrella magnolias in the metropolitan area, especially in Takoma Park, trace to plantings by those Agriculture employes.

A guidebook to Washington's fantastic variety of trees, tentatively titled City of Trees and due out next year, is being compiled by Melanie Choukas-Bradley and Polly Alexander. The two botanists, working on a grant from the American Forest Institute, discovered the magnitude of their task as they went beyond such charted areas as the Capitol and White House grounds to spot a kousa dogwood just off Scott Circle, a koelreuteria (golden rain tree) in Mount Vernon Square, and "two nice Chinese scholar trees" at New Hampshire Avenue and 21st Street NW.

They noticed the pale green blossoms of another scholar tree, so named because the Chinese planted them on the graves of learned men, in the Victorian garden near the Smithsonian castle, and nearby on the grounds of the Agriculture Department they recognized a rare pond cypress. Three Amur corks from Manchuria turned up, with their distinctive thick bark and fat black berry-like fruit, two on the east side of the Library of Congress and one west of the Tidal Basin.

It would take a trained botanist to recognize a kousa dogwood, it's so similar to its American cousin; the petals of the white blossoms are more pointed and a kousa seems to bloom longer. Many Chinese and Japanese trees do well here, Choukas-Bradley says.

The Asian tree best known in Washington is the gingko, regarded with less than fondness by shopkeepers when its red-purple berries squash on sidewalks and get tracked inside. But urban landscapers love ginkos because they seem impervious to auto emissions and dog depradations and thrive along busy sidewalks, enlivening the city at this time of year with brilliant yellow foliage. Botanists love gingkos because they are probably the oldest tree species going. Their hardiness seems due to their structural simplicity; like sharks, they survived because of their primitiveness.

Dr. Fred Meyer of the Arboretum marvels at the gingko's endurance under attack, recalling a stand of the fan-leafed trees on the Mall that were cut down to clear the view. The logs were stacked on the site of a future museum.

"Five years later, the logs had sprouted and rooted," Meyer said.

Regarded with a similar mix of affection and distaste is the royal paulownia, a Far Eastern monster inexplicably named after a princess of the Netherlands, that extablished itself here after it was introduced into New York in 1834 and escaped. It's a big tree -- one in Philadelphia is 105 feet tall -- and gets big fast; the way it grows like a weed is why some people consider it as one. Paulownia leaves are like elephant ears, often more than a foot in diameter, and its blossoms are violet clusters like bunches of grapes. Just recently a use was finally found for the paulownia's spongy wood: fittingly, logs are being shipped back to Japan, where they are chipped and fed to cattle.

The biggest tree in Garfield Park at 1st and F Streets SE is a paulownia, but the place to see paulownias in quantity is along the George Washington Parkway as you head north toward the turnoff for the CIA.

One of the most charming trees in the area is an American beech at the corner of Maple Avenue and Sligo Creek Parkway in Takoma Park that is known to be at least a century old and presumed from the carvings on it to be well over that. The carvings are the names of presidents from Washington through Andrew Johnson, plus "Lt. Gen. U. S. Grant," "Samuel Fenton" (presumed to be the carver, probably a Union soldier stationed in the area among troops protecting the capital in the Civil War), and a Lincoln word game. In 1948 the tree was preserved when threatened by road wideners.

In almost every jurisdiction in the area, there's a Cedar Lane or Cedar Street or Avenue or Road. To botanical purists, all are misnomers -- the trees the streets were named for are junipers; there is no true American cedar. There are, however, a few true cedars here, all imports or descendants of imports, including a Turkish form of the biblical cedar of Lebanon. It's in Chevy Chase, on Connecticut Avenue near that Japanese white oak and was probably planted by David Fairchild about the same time, in 1912.

"It's a big tree and you can't miss it," says Meyer, "and probably the biggest in the country, or maybe I should say bigger, since the only other one we know of is in a arboretum in Boston."

There are two handsome atlas (silver) cedars from North Africa in Franklin Park at 13th and K Streets NW and a striking deodar cedar from the Himalayas at Arlington House in Arlington Cemetery.

Several fine old trees stand at the Soldiers' Home, particularly a massive Osage orange near the Lincoln Cottage. And nearby in Rock Creek Cemetery is the Glebe Oak, which has documents proving it was a big tree in the early 1700s.

Equally ancient is the Forest Oak outside the C&P Telephone Co. office at 5 Frederick Ave., Gaighersburg. That white oak was big enough to be a landmark on an Indian trail in 1755 when Gen. Edward Braddock built his road west and a tavern built beside it became a regular stop on the stage coach line that followed. Gaithersburg used to be called Forest Oak.

There's no dating the age of what doubtless is the oldest tree on the Capitol grounds, an English elm in the northeast quadrant that now has to supported by cables. It may be the tree Olmsted referred to on his arrival here in 1874 and described the Capitol grounds as "sylvan juvenility." There was, he wrote, "but one tree . . . that yet approaches a condition of tree majesty."

During the next 12 years, Olmsted tore up most of the grounds to improve the soil, deep-plowing, bringing in oyster-shell lime, swamp muck and manure. He planted 229 varieties of trees and shrubs, letting nothing stand in the way of his concentric design of walks, terraces and drives.

Almost nothing. One day in 1875, Sen. Simon Cameron of Pennsylvania, strolling in the southwest quadrant of the grounds, saw workmen about to cut down an American elm for one of Olmsted's walks. He stopped them, raced back into the Capitol and got a bill passed to save the tree. It's still there.

Only about half of the varieties Olmsted planted have survived on Capitol Hill, but many others have taken their place, including rareties such as the bigleaf magnolia with its 18-inch leaves and 12-inch yellow blossom and the twice-blooming Higan cherries, which startle visitors by bursting forth in the late fall, some years as late as Christmas.

In the yard at 5031 Reno Rd. NW is a three-story-tall living fossil, a dawn redwood or Metasequoia. Until the 1940s, the species was thought extinct, seen by botanists only in fossil form. Then, in a remote area of China some living ones were found. Seedlings were brought to this country, planted at places like the Arboretum, and thrived. The Arboretum has some 70 feet tall.

In this day of Guinness Books of Records on the best-seller lists, "biggest" has acquired status in tree circles. Several area trees turn up in the National Register of Big Trees, the American Forestry Association's roster of the biggest of each kind of tree in the country, calculated by a point system from height, spread and trunk circumference.

One of the local champions was a mountain maple on the Capitol grounds, suitably labeled until early this year when Choukas-Bradley took a look at it and recognized it for what it really was, a Cappadocian maple from Asia. So much for the record books.