SAINT ELIZABETHS for a century or more has existed as only a glimpse outside the corner of Washington's eye. Saint Es always seemed like a hidden hamlet in a never-never land, a place to go only under duress.

Saint Elizabeths Hospital occupies a commanding height, a plateau overlooking the Anacostia River. At 150 to 170 feet above sea level, it's a promontory capable of being defended, like a castle on the Rhine. Saint Elizabeths hides its charms behind its thousand tall and luxuriant trees of some 150 species. It sees without being seen -- from The Point, its belvedere, Washington has no secrets. Our rivers, domes, towers, steeples, columns, ships, memorials, mounts, trees and bridges are spread in a panorama for the viewer from Saint Elizabeths.

Travelers who brave the ascent to the plateau find an amazing village -- sanctuary, refuge, asylum, retreat, shelter -- frozen in the mid-19th century, preserved in spite of Washington's penchant for change.

Frederick Law Olmstead, of Capitol grounds and Central Park fame, laid out the lush but decorous park in 1901. Thomas U. Walter, architect of the original 1855 Center Building, lined it up with the Capitol's dome, another Walter work.

We decided to make the trek to Saint Elizabeths, not to see the treatment centers or patients, for they are another story, but to enjoy the institution's overlooked glories of architecture and landscape.

In the 1840s and 1850s the remarkable Massachusetts reformer Dorothea Lynde Dix, having spurned a fiance who wanted her to quit her job as a teacher, began an international crusade for humane treatment of the mentally ill: compassionate companions, serene surroundings and a luxuriant landscape. By the time of her death at 83, in 1885, she had established 33 state mental hospitals and inspired the founding of almost a hundred more.

In 1852, Congress surrendered to Dix and her footsoldiers in their battle for medical reform and appropriated big dollars -- $100,000 -- to establish the Government Hospital for the Insane. Interior Secretary Alex H. Stuart described it as "a lunatic asylum for the insane of the District of Columbia and of the army and navy of the United States."

Dix and her so-called "moral" healers put great faith in nature's medicine: strolling flower-bordered walks, sheltering under native and exotic trees, and most of all, living in surroundings secluded from the taunts, terrors and temptations of the town.

Dix herself picked the site. The tract had been called Saint Elizabeth's at least by 1660, according to documents found by researcher William Whitmore M.D. It once was owned by a man whose wife and daughter were both named Elizabeth. Legend also links the name to Saint Elizabeth of Hungary, a medieval noblewoman who devoted her fortune to helping the sick and the mentally ill.

Saint Es psychiatrist and historian Kenneth P. Gorelick says Dix talked owner Thomas Blagdon into accepting the $25,000 Congressional appropriation, instead of his $40,000 asking price.

In 1855, only three years later, the first patients were admitted, beginning 135 years of treatment, much of it innovative. "Patient No. 7, Richard Lawrence, was the first would-be presidential assassin," says Dr. Gorelick. "His two flintlock pistols mysteriously misfired at point-blank range when he attempted to gun down Andrew Jackson at the Capitol."

Since then the hospital has been given custody of a number of others bent on assassination. John Hinckley, the most recent presidential assailant, is in the John Howard Pavilion for the criminally insane, on the East Campus.

Another famous inmate, from 1946 to 1958, was poet Ezra Loomis Pound. He was indicted for treason during World War II, ruled mentally unfit, and kept at Saint Es in what were said to be luxurious circumstances, including a room next to the superintendent's ceremonial suite.

During the War for Southern Independence (to put a more civil name to it), the hospital accepted wounded soldiers, especially amputees. A prosthetics factory was opened on the grounds. The soldiers didn't want to write home from an insane asylum, so they used the old name. In 1916 Congress made the name Saint Elizabeths official (omitting the apostrophe, to the intense irritation of generations of copy editors).

Like too many of its patients, for far too many years, Saint Elizabeths was a subject to be changed, the less said the better, a place often forgotten, a problem to think about tomorrow. But now Saint Elizabeths, still the largest federal mental health facility, has come into full view.

This fall the federal government transferred the east campus, with its newer 20th-century buildings, 1,470 patients and 3,000 staffers, to the District of Columbia.

The west grounds are promised to the city, but won't come under its full control before 1991. Some 80 historic 19th-century buildings and the panoramic belvedere are all on the grounds west of Martin Luther King Avenue (formerly Nichols Avenue, after the hospital's first superintendent Charles. H. Nichols).

Meanwhile, plans are afoot. While the city and business interests consider ways to develop the land and bring more jobs to Anacostia, some have other ideas.

Friends of Saint Elizabeths, sparked by Barbara Bick and Richard Ridley (a Washington architect who has done a vast amount of research on the institution's past and present), have developed a mixed-use plan, centered around a therapeutic community of sheltered housing, and preserving the great Center building as the Anacostia Museum.

The National Register of Historic Places, after extensive research through the old files and close measurements and inspections of the old architecture, in 1979 declared the west campus a Historic District.

Before we went to see for ourselves exactly what Uncle Sam has seen fit to give us, it seemed prudent to inquire if we would be welcome -- and safe.

"The grounds are open any time during the day. And you won't find any more mentally disturbed people on the grounds of Saint Elizabeths than on F Street," said Dr. Harold Thomas, just before his retirement as spokesman for the mental health facility. "The ones you might see aren't, as they say, 'stark raving mad.' Most of those on the grounds are settled, middle-age types. Some will wear coats and ties. Others who may have been neat and clean when they left their rooms might not necessarily still be in first-class shape.

"Chances are you won't know who's a patient and who's a sightseer. Because they don't see that many people, they may come over and speak to you. You should respond with respect. After all, 30 percent of Americans eventually need mental care."

After two weekends rained out by thunder and lightning, a crystalline Saturday beamed on us. Crisp air filled the lungs, cleared the head and cooled the brow. The brilliance of the light revealed sharply drawn lines, silhouetted shadows, saturated colors -- a day to climb a hill and see a sight, to travel in time to another century, another sensibility, before it all vanishes like dreams that fade in the sun.

Though Saint Elizabeths is well within the District of Columbia, it's as difficult to find as the solution to the problem of what to do with unused historic buildings.

We almost didn't go, despite the glittering day. We couldn't find the map, and as the photographer said, "If I'd known the map wasn't in the trunk, I'd have been too lost to make it to work yesterday."

We saw a great deal of the land southeast of the Anacostia River.

While he cursed for fear the morning light was fading, we circled around in search of Saint Elizabeths. When we finally found the gate, it was by accident and happenstance, our usual way with or without maps. The way is simple, after you find Anacostia and after you find 2700 Martin Luther King Avenue. Turn west through Gateway One.

We didn't. Somehow, we came down Alabama Avenue and went in Gate Five, in the newer east section, and drove around forever before we found the Redwood Drive underpass which leads under Martin Luther King Avenue into the west historic section. The 20th-century section, still a mental health facility, is worth driving through, especially noting its four 1902 buildings, but it's not as interesting as the 19th-century historic section -- mostly either vacant or used as offices -- which our walk covered.

Both east and west, new and old sections, are bounded by Anacostia Freeway (I-295) on the west, Barry Farms neighborhood on the north, Suitland Parkway on the east, and Congress Heights neighborhood at the south. Eventually, the world, by way of two Green Line Metro stops at Anacostia and Congress Heights, will come to the area. Anacostia station will have parking for 1,300 cars, the largest of the District stations. The Metro line will tunnel under the Anacostia River. The opening is scheduled for 1991.

Saint Elizabeths is sequestered behind a fine wall, originally designed to keep people out as well as in, for fear the patients would be victimized by strangers. Some of the wall is brick, made on the place, and the rest is quarried stone. Handsome brick coping covers both. Work on the wall began in May 1858 and was largely finished in 1869, even though they used up the bluestone from the Georgetown quarry and had to quarry a siliceous conglomerate near the hospital.

Gatehouse One is its own reason for going in that way. The charming "gothick" (Victorian Gothic) cottage, built in 1874, is brick on a quarried stone base. It has only one proper story but the attic is finished. Its steeply pitched slate roof is decorated with cast-iron ornaments, Victorian gingerbread that looks good enough to eat. Dormers peer out at the passersby.

The guards at the gate are very helpful, as are those who circle the grounds in patrol cars. Stop and ask where to park and for the useful map of the grounds. Though it doesn't exactly list two prime landmarks, The Point and the Civil War Graveyard, it does help you figure out where those are.

Visitors are welcome from 9 a.m. to 9 p.m., but not their cameras, unless you have a good reason and get permission beforehand. To protect the privacy and dignity of patients, none may be photographed. Your lunch basket isn't welcome either, but you can eat in the staff cafeteria, Building 70, just before the underpass that connects the two sides of the campus. Or you can do as we did: await the afternoon light at Taverna the Greek Islands on Capitol Hill; it isn't that far, and the baked chicken was delicious.

Though the hillside is steep, the drives curve gently around, with flower beds blooming with color just when you need them. This is a walker's delight, because there's very little traffic. We only encountered a solitary squad car, and that driven courteously.

When Richard took his photography gear out of the car, a man, nattily done up in a brown suit, and taking a constitutional in front of the administration building, engaged him in conversation about Fuji film, making about as much sense as most photographers. Later, another man stopped by to ask politely for a donation to his private soda fund. A group of about six, led by an attendant walked by, enjoying the day. But except for an occasional security officer, we saw no one else.

We wished we'd brought along a tree guide. A list compiled by Pete Atkinson, the horticultural chief of Saint Es, says that Alvah Godding, son of the second superintendent, brought in 170 varieties of plants from Asia, the Caucasus, Greece, Bulgaria, China, Japan, India, Persia -- and even redwoods from California. He suggests looking for Styrax obassia, a Japanese tree; crape myrtles in red, pink, purple and white; Juglans nigra; and a large Japanese yew. The greenhouses now grow carnations, Easter lilies, geraniums, hydrangeas, chrysanthemums and poinsettia. The garden areas raise gladiolus and other cut flowers and test plant introductions for the Agriculture Department.

The pergola which used to stand in the circle of holly trees is now in the Smithsonian, but the area still has the air of a place waiting for a ritual. Nearby, Japanese flowering cherry trees wait for April, along with the native and the Japanese dogwoods. The large white oak near the flagpole in front of the administration building was planted by John Scott just before he left for the Civil War. Huge century-old white oaks line the avenue to the Center Building.

The two English elms by the Center Building look like royal guards. A rarer variegated leaf variety of English elm stands up against the building. And a great American elm escaped Dutch Elm disease to grow to 100 feet near the circle down from The Point. The American hollies are said to be the largest in Washington. A black haw may be older than the hospital.

We found that it isn't necessary to follow any plan on exploring the grounds; you may see more if you get lost. At the gatehouse, if you take the north road called Cedar Drive to the right, you'll come to Center Building, the original hospital itself, and still the most impressive pile of brick around.

(Of course, we didn't go that way. We took Hemlock and Birch and perhaps even Holly streets, and wandered about like babes in the woods.)

Center Building, the oldest, sits on the highest spot, towering over the rest, three to four stories high in its formidable Collegiate Gothic revival style. Its widely copied plan is called Kirkbride after a physician of the day, who some say was one of Saint Es original 13 doctors.

Its central tower begins with a portico or porch on the ground level. Above it hover two balconies edged with elaborate cast-iron decorations. Its embattled parapets are castellated in case anyone wants to use it for bow and arrow practice. Its buttresses on the corners give a stable air.

On the lower floors, the oriel windows rise tall and important, to bring in the healing sunlight, growing smaller as they go up. Cast-iron hood moldings still decorate the windows. Walter planned the tower to have magnificent views of the Capitol and the rest of the capital, but the trees grew so tall that the spring and summer view is leafed over.

The west (1856) and east (1861) wings or lodges, also by Walter, stretch the whole grand building to 750 feet. Though it was planned for 90 patients, by 1874 more than 600 lived there. Like a castle, which it so closely resembles, the building provided not only living quarters for patients and staff, but also kitchens, furnaces and recreation rooms and a chapel.

A narrow-gauge railroad, though out of service since 1969, ran the length of the basement, to bring supplies to the kitchen. Below the railroad tunnel is a pedestrian passage, a part of the mysterious and widespread underground tunnels honeycombing the hill. The building is heated by the old coal-fired gravity flow furnace.

As late as 1967, the hospital had its very own railroad line with a steam switch engine to bring coal for the boilers providing heat and hot water to the 130-odd buildings.

The brick was fired on the place and the woodwork milled from standing timber. It was 1881 before the kilns and mills were dismantled from the front lawn of the Center Building.

You have to plan ahead, call and make an appointment (Monday through Friday only) if you want to see the museum in the original Center Building. Wilhelmina Carey, deputy chief of the logistics management branch, found most of the treasures when she was head housekeeper. She's stuffed 10 rooms with furniture, objects and memorabilia found and saved, sometimes just in the nick of time.

The museum was once the superintendent's 21-room apartment and offices. Now it includes the boardroom, still used for conferences. Among the 1,700 objects are furniture from 1855 to 1940, a Recamier fainting couch, and original drawing-room chairs and sofa with shields and medallions.

The museum is almost a shrine to Dorothea Dix. Her portrait hangs over the desk on which she wrote the first draft of the bill establishing Saint Es. The trunk that followed her around the world as she preached on behalf of the mentally ill stands ready. The canopied four-poster bed is said to have been used both by Abraham Lincoln on overnight visits (his feet would have stuck out), and (but not at the same time) by Dorothea Dix who lived for some years at the hospital. She was so small her feet must have felt cold and lost in so big a bed.

The 1853 architect's drawing of its plan and the 1904 model of the buildings and grounds made for the Saint Louis World's Fair are worth a careful look.

Call Ms. Carey at 273-7719 for an appointment.

The bakery still stands and cooks bread and doughnuts behind the Center Building. The icehouse keeps its cool down on Ash Street. Out a way were the stables and the machinery and carpentry shop to take care of the equipment for the farm, which originally spread over most of the grounds.

The Civil War cemetery, now mostly obscured by trees and shrubs, is down the hill a bit from Center Building, north of Building 118, the warehouse and laundry. We didn't venture downhill to take a closer look, for fear of snakes. We were wise. Carey says it isn't safe to go down without arranging for a tour with her office, so she can have the jungle beat back.

But after the leaves fall, from I-295 or South Capitol Street we'll be looking for an eerie white cross which appears on the hillside. From 1864 to 1866, the headstones on the soldiers' graves were placed in such a way that from a distance below, they formed a white cross.

At the gatehouse, we went south, up the hill, on Redwood Drive to arrive grandly in front of the 1902 administration building. The National Register calls its style, "American Mediterranean architecture." It's not as impressive as the Center Building, and certainly not as frightening, but hardly anything is. It commands Redwood Drive, which comes straight up from the gatehouse. Shepley, Rutan and Coolidge designed the building. The great architectural firm was one of the most important in the early 1900s, when H. H. Richardson was its designer (and is again today: Its successor firm, with Jean Paul Carlhian as designer, planned the new Smithsonian underground quadrangle museums).

The portico is fancy enough, held up by six Roman Doric columns, topped by a small clock tower at the peak of the hipped clay tile roof. Underneath, the entrance is through a white stone arch. I walked along its side to admire the arched windows and balconies and the way stone framed the bays of three windows. The building is flanked by two more tile- roofed structures with pleasant screen porches. Its front lawn is a spacious green, a rough elipse, punctuated with flower beds. The year 1902 marked the largest expansion in Saint Elizabeths history, increasing the space by 82 percent.

From the administration building we walked a block or so to 1908 Hitchcock Hall, charming with its circular window and mask of drama on the facade. The theater is used not only for entertainment and lectures, but also for psychodramas.

Down Redwood Drive, we passed "Rest," built in 1883 as the morgue, reborn as the circulating library in 1929.

The small Fire Engine House (35 by 25 feet) looks as though it came out of a toy railroad village. Actually it came from about 200 feet north, where it was built in 1891 but was moved to Hemlock Street about 1905. Its five-story tower supports a clock with four faces on the top. The three-foot bell below rings three times a day and once on Sunday. It's inscribed with the cryptic legend "At morning call awake, at weepers {sic} slumber take."

On our way out, down Cedar Drive, we saw the Borrows Cottage, a pleasant Victorian house with tall narrow windows. A Mrs. C.Z. Borrows built it for her daughter and nurses in 1891, with the agreement that when the woman died (which happened in 1917) the cottage would go to the hospital. It's not small, with 10 bedrooms and baths.

On other once-residential buildings, now either vacant or used for offices, we admired the pleasant semicircular porches, some screened, built to allow the patients to take advantage of the hill's breezes. For less pleasant weather, the covered walkways between other buildings serve.

We went twice to The Point, once before lunch, and once after. The Point is on a promontory encircled by Golden Raintree Drive, leading off Cedar Drive in front of Center Building. Atkinson thinks it may have been the site of Fort Snyder, a Civil War fort. A big native red oak stands at the ready to feed the squirrels.

And this is the reason to come, to look down on Fort McNair, the Washington Monument, the Cathedral, the Old Post Office tower, the Capitol dome, the Library of Congress dome, boats and bridges and all of Washington brick, stone, and green.