By Anne H. Oman

IF YOU'VE NEVER CLIMBED Mount Hamilton, now's the time. The azaleas, rhododendrons and Mayapples that cover the slopes and border the paths leading to the top are just bursting into bloom. It's a gentle climb, because this "mountain" is only 239 feet high. But even if you had to huff and puff a bit, the view would be worth it. From the bench at the top, you can see the Capitol, the Library of Congress, the Washington Monument, the Washington Cathedral, the Shrine of the Immaculate Conception and the Anacostia River.

Mount Hamilton, one of the highest points in the District, is in the National Arboretum, a 444-acre preserve in Northeast Washington.

The Arboretum comes to us courtesy of the Department of Agriculture and conducts research on trees, shrubs and herbaceous plants. That benefits the whole country, of course, but we Washingtonians also get hills painted pink with 70,000 azaleas; valleys of ferns and wildflowers; paths through the woods high above the Anacostia River; ponds that are home for geese, wild ducks and catfish; a stand of ancient dawn redwoods; meadows and streams and virtually every kind of tree that it's possible to grow in this climate.

All these things are yours to enjoy year around, but this time of year is something special. The dogwoods are in flower, and the hills are bright with magnolias, crabapples, cherry trees. In the woods, the wildflowers are popping out. And, whether you prefer the kind of woodsy garden that wildflowers thrive in, a formal boxwood garden, a daylily garden or a Japanese garden that you enter through a dark little forest of Japanese crytomeria trees, you'll find your kind of garden here.

"Gardens are like ties," says the Arboretum's ebullient director, Henry M. (for Marc) Cathey. "I want a great variety."

The latest garden in the variety is the National Country Garden, dedicated to anyone who's ever painted an old tire and stuck plants in it. In the National Country Garden, however, the tire, and all the trellises, benches and so forth are painted lavender. Flags fly from the structures, making the garden look like a Disneyesque version of a medieval fair.

"You have to have the sizzle before you have the steak, and lavender was last year's merchandising color," explains Cathey with an iconoclastic twinkle in his eye. "Arboreta have always been third-person gardens. You go to them and see a garden you could never do. We have all the rare plants that can grow in the Washington area here, but that keeps people distant. The country garden is talking about people gardening."

In the garden are plants and trees youdon't have to be a serious gardener to grow: daffodils and strawberries, tomatoes and apple trees.

Cathey's next project, now in the fund-raising stage, is a classical garden on a hill, a sort of instant ruin consisting of 22 of the Corinthian columns that used to grace the East Front of the Capitol. The East Front was redone during the Truman administration, and the 14-ton sandstone columns, designed by Benjamin Latrobe, were left lying in a weed patch beside the Anacostia River. One of them is now on display at the R Street entrance to the Arboretum.

"They're calling it 'Marc's Stonehenge,' " says Cathey with a chuckle. "It will have fountains and naturalistic plantings . . . When that's finished, we'll have all three of the elements I wanted. That will be the classical, and we already have Asian -- in Asian Valley and in the Bonsai collection -- and we have contemporary, represented by the country garden."

In addition to adding to the Arboretum's collection of gardens, Cathey has made it more a people place, by adding a picnic area (adjacent to the National Country Garden) and by stepping up security with a patrol guard system.

"It's a safe place to come," says Cathey. "The Arboretum is for people. The plants are here for the people."

Well, there's your invitation. Pack a picnic. Stop first at the Administration Building -- entered by a bridge over a pool where Japanese koi swim -- and get a map and some brochures. Then wander among the dogwoods or dwarf conifers or rhododendrons. And don't miss the following special gardens. THE NATIONAL HERB GARDEN

With Miss Kitty at her heels, Holly Shimizu is giving a visitor a tour of the National Herb Garden at the Arboretum. Miss Kitty is charged with keeping moles and mice out of the garden but sometimes, understandably, she gets into the catnip. Shimizu, a veteran of herb gardens in England, Belgium, France and Germany, is curator of this garden.

"We define 'herbal' as plants of use to man -- plants that aren't just ornametal, and not vegetables," explains Shimizu as we walk up a boxwood-lined path into an outdoor reception area. "There are really three gardens: the Knot Garden, the Historic Rose Garden and the Specialty Gardens. Each garden has a different texture. They're like 'rooms' in European gardens."

The first room you see might be likened to a sunken living room because you view it from above. It's the Knot Garden, a series of interlinking chains formed by dwarf evergreens.

"Knot gardens were very popular in the Middle Ages, and there's one at Shakespeare's birthplace," says Shimizu. "The patterns came from French embroideries and Oriental rugs."

The Historic Rose Garden, which blooms mainly in June, is a room bounded by vine-covered trellises and hedges, and the roses are living proof that a rose is not just a rose.

"This is Apothecary's Rose," says Shimizu. "It was cultivated in France in the 13th century. The petals have an increased fragrance when they're dried. This is Rosa damascena -- it's the source of attar of roses. And this is Eglantine Rose. Its fragrance is emitted through the leaves, that smell like pippin apples in summer. They used to plant it near a window so the fragrance would blow through the house."

Although originally prized for their herbal properties, roses, in Victorian times, began to be cultivated more as showpieces, according to Shimizu. The now very popular hybrid teas were first cultivated in 1867, and are represented in the collection by La France, the first hybrid tea rose. European roses used to bloom only once, according to Shimizu, until they were crossed with long-blooming Chinese roses in the middle of the 18th century. Most of the old varieties of roses (many of which are now in the Arboretum's collection) had all but died out, until plant collectors found them in cemeteries and monastery gardens and started cultivating them again.

The biggest 'room' in the herb garden is an oval consisting of ten specialty gardens, with everything from a dye garden to medicinal herbs grown by the Greek physician Dioscorides, to industrial herbs, such as spiderwort, which is being cultivated around nuclear power plants because its stamens change color in the presence of radiation.

"This is dyer's woad," says Shimizu in the dye garden. "The colonists used it, but they needed urine to ferment it. That's why the dyers' houses were put far away from everyone else's . . . And this is celandine. You can see the yellow in it," says Shimizu, rubbing it against her finger, where it leaves a yellow mark. "And this is bloodroot. The Indians used that to paint their faces."

In the colonial garden, you can find one of the world's more useful herbs: costmary. The early Americans stuck a leaf of it in their Bibles where it served two purposes. It acted as a bookmark, but the herb's properties as a stimulant were more important. During long, soporific sermons, colonial churchgoers bit off pieces of costmary to keepawake. ASIAN VALLEY:


Barry Yinger, curator of Asian collections at the Arboretum, is standing at the edge of what used to be a gully but is now a living version of an Oriental scroll painting, complete with waterfall, pagoda and plants collected in Asia. Tramping down a winding path lined with Korean boxwood, Yinger explains that Asian Valley is really a collection of different Asian gardens, with more to come.

"The central valley contains plants from all over temperate Asia," says Yinger. "The section on the east has native Japanese plants. The small valley to the west will be China Valley, when it's finished. There'll be a path down to the Anacostia River. The Japanese part of the valley is garden-esque; but when China Valley is finished, it will look like you're walking through the woods in China. At the top of the hill, across the road, we hope to put in a Korean garden . . . We have a lot of dreams."

Yinger studied both horticultural and Oriental languages in college and learned Korean while working in a botanical garden there.

"I'm devoted to the plants of East Asia," says Yinger. "It grew out of my learning that many plants in North America were related to plants in East Asia. There wasn't enough information about them in English, so I learned the languages . . . Korea is the great orphan of the Far East, and it played a pivotal role. Many Japanese gardens were built by Korean artisans, but Koreans like color more. They're bolder in their use of materials."

On a recent collecting trip to Korea, Yinger brought back many native plants that are being propagated in a greenhouse. Among them are cold-hardy camellias Yinger found on some islands near the North Korean border. They may someday be placed in Asian Valley's camellia collection, which has been decimated by recent hard winters.

At the Arboretum's other Asia, the National Bonsai Collection, fifty-plus trees -- elms, pines, crabapples and mini-versions of trees growing elsewhere on the grounds -- are growing very, very slowly in pots. These trees, some of which are more than 200 years old, are kept small by ancient techiniqes of pruning and controlled fertilization. Curator Robert Drechsler is carefully plucking a blossom off a tiny hundred-year-old Japanese flowering quince.

"The flowers and fruit are normal size -- it's part of the genetical makeup," explains Drechsler, who is removing some of the blossoms so they don't weigh down the branches.

The bonsai collection, a bicentennial gift from Japan, is growing a lot faster than the plants themselves. Recent acquisitions include two bonsai from the collection of King Hassan of Morocco: a persimmon and a Japanese white pine. There's also a made-in-America bonsai that, Drechsler hopes, will be the nucleus of a larger American bonsai collection. It now sits among the Japanese bonsai, a mini-forest of tiny junipers with a miniature Shinto shrine. The 55-year-old composition, created and donated by John Naka of California, is called "Goshin." It has 11 plants -- one is for Naka's wife, one is for himself and the rest are for his children and grandchildren.

Drechsler, who teaches the techniques of dwarfing trees and creating your own bonsai at the Arboretum, root prunes the trees every other year. He claims he has no favorites.

"Each has a feature of its own," he says. "They're like a bunch of kids. Sometimes one looks good to you, sometimes another." A STROLL IN FERN VALLEY

When spring comes, everybody's fancy turns to a walk in the woods. Here's a wood that has not only a stream and bridges that cross it, but also ferns, trees, wildflowers and shrubs that speak up and tell you what they are. At least the trail guide (which you can pick up either in the Administration Building or at the beginning of the trail) tells you what they are. The name of the woods is Fern Valley.

The trail leads you past witch hazel (the plant whose bark and roots are distilled in alcohol to make the name-brand astringent) and Christmas fern (whose fronds stay green all winter) and white oak. (Do you know how to identify white oak? "The ashy gray bark at eye level and below is broken into small squarish blocks, while the upper bark is almost shaggy," the trail guide explains.

You'll also learn to identify wild ginger -- by its jug-shaped, reddish-brown flowers, which are the scene of a bizarre mating dance by gnats that apparently confuse the flowers with the kind of mushroom they like to lay their eggs on.

The wildflowers in the valley -- including bloodroot, trilliums, spring beauty, and dutchman's breeches -- are often spread by ants. The seeds have fleshy wings that the ants carry away and eat, dropping the seeds along the way.

You can also see a killer in action -- the chestnut blight. Virtually all the American chestnut trees in this country were killed by this blight, a fungus that attacks above-ground sections of the tree while leaving the roots alone. The roots of the chestnut in Fern Valley keep sending up sprouts that die before they have a chance to grow.

A plant story with a happier ending is told on the self-guided tour. Oconee-bells, or Shortia galacifolia, is a rare plant with white, bell-shaped flowers. In the early 1800s, a French botaTAKE 208694 PAGE 00006 TIME 10:48 DATE 04-19-85 nist in America collected a specimen that was much admired by other botanists but could not be found again in the wild. After a 40-year search, it was rediscovered in the southern Appalachians.

The mountain laurels you'll find on the hillsides of Fern Valley are poisonous, but the hemlock trees aren't. Contrary to popular belief, the poison Socrates took didn't come from a hemlock tree but from another plant called hemlock that's related to parsley and looks something like Queen Anne's lace.

This is a walk in the woods where you learn things like that. But be sure to take time to smell the flowers (not the dark red flowers of the star anise -- they smell like rotten fish), and listen to the birds singing and the brook babbling. OTHER ARBORETUM WALKS

The Azalea Loop Trail starts at the Morrison Azalea Garden and winds up the slopes of Mount Hamilton to the top. The view from the top and along the trail is spectacular.

You can also have your hollies with a view. Park at the parking space on Holly Spring Road and walk down the path lined with English hollies. Then cross Hickey Hill Road and do the American Holly loop. The bottom of the loop overlooks Kingman Lake, a wide expanse of the Anacostia River.

Dogwoods -- 70 different varieties -- bloom on a lush lawn known as Dogwood Circle, also off Hickey Hill Road. An unnamed trail at the edge of the lawn will lead you through a wooded area high above the river.