At night in the house where the walls are all of glass, when the snow is falling all around, architect Philip Johnson feels "as if I'm on a celestial elevator, floating . . . not straight up, but gently wafted."

Describing the house at its best, Johnson almost trips himself up, interrupting one vision with another the nights when the fog rises slowly from the valley, envelops the house "and makes me feel like a Chinese philosopher" (which he resembles with his close-cropped white fair and dark-rimmed glasses); the nights of brilliant stars and the dawns when he wakes to see "beautiful birds against the sunrise." For Johnson, the house is a lover in whom he delights, always finding new charms, discovering old enticements, reveling in the seduction of its sensuality.

Johnson is a tall, wiry man with the quick, controlled movements of a fencer. He speaks as elegantly as he books - crisply with great wit and spare charm, with always the right word, the fortunate epigram and the spice of the unexpected and irreverent. (He once told a roomful of the respectful at an American Institute of Architects seminar that what they really should be talking about was not design but liability insurance.) In art and architecture circles, he is counted a generous man - of his money, of his time and of his genius.

At 72, after a serious heart operation a few years ago, he looks as timeless and well preserved as his house. ("When I turned 70, it was like beginning again," Johnson said. Everything gets easier. I don't have to prove anything anymore. I can say to hell with everything.")

The glass house that Johnson, a life-long bachelor, designed for himself, and the entire five-building, 32-acre weekend retreat outside New Canaan, is considered by many authorities to be the finest residence built in the United States in this century, as well as a major influence in the architecture of out time, arousing strong passions of desire, disbelief or distaste.

The estate is a museum of 20th-century architecture. Over the past 29 years, Johnson has designed its buildings (the glass-walled main house, the glass-roofed sculpture gallery, the guest house with port holes, the pond pavilion and the no-glass painting gallery) as an expression of his personal progress as well as a progression of the architectural tastes of out time.

Johnson pointed out to visitors the other day that the house, on a promontory half-way down the hill, is "cuddled by the hill." He cites the Japanese belief that such a site traps the bad spirits below and catches the good spirits from above. Another architect, Frank Lloyd Wright, was fond of saying a house should be of the hill, not on the hill. The house overlooks the pond and pavilion. On the other side is a round, white swimming pool with a long granite bench. Neat, short grass with wildflowers for pattern carpets the estate.

The glass house was completed in 1949, while Johnson was still a disciple of architect Ludwig Mies van der Rohe. "Nothing is changed in the house since I built it," Johnson says. "I treat it as a preservation."

Its one room, 56 feet long, 32 feet wide and 10 1/2 feet high, is interrupted only by the circular brick pillar that extends through the roof. The pillar contains the semi-circular bathroom, opulently lined in pigskin leather. The other half is a castle-sized fireplace topped with a curving hood of glass.

Lights atop the roof spotlight the trees at night. A few fabric sunscreens slide on a track to keep out the glare.Doors set one to a wall provide through ventilation. The brick floor is laid in a chevron pattern.

Most of the furniture in the house dates from 1929 when Johnson wrote Mies van der Rohe and Lily Reich in Germany to buy a whole set of their latest designs - the first to come to the United States. The living room furniture - two Barcelona chairs, an X-frame table with a glass top, a leather-covered chaise lounge (upon which Johnson, with an agility remarkable in anyone of any age, manages to curl up) sits upon a white rug.

The table has a copy of Playboy and a New York newspaper on it. (Though, according to Calvin Tomkins' masterful profile of Johnson in The New Yorker last year, one friend chastised another for putting her pocketbook on it, saying you don't stew things about in a Miesian house. Tomkins also tells the story about Frank, Lloyd Wright, who came in the house, looked around, and asked Johnson if he should leave his hat on or off and was he inside or out.)

A Nicolas Poussin painting, "The Death of Phocion," rests on a Johnson-designed easel. A large Elie Nadleman sculpture to two women stands across the living room. A geranium stands on the floor not far from several goodsized Ming trees.

Johnson says that if he has to write a speech - as he does at the drop of a pencil - he can't do it in the glass house. "The squirrels distract me too much." He works on a table by Joe Columbo (designed for poker though Johnson doesn't think it would work) in his windowless sculpture gallery elsewhere on the estate.

In the bedroom, screened by a headhigh storage wall (everything inside is scrupulously arranged), is a large bed, a leather-topped table and a leather and chrome chair (both Mies/Reich designs). In the dining area is a marble table on pipe legs designed by Johnson, four more Mies chairs, and a counter with a small refrigerator, sink and stove, hidden under a fold back top.

"When I had servants, I always made them keep it closed, but now that I get breakfast and lunch, I don't bother. I don't really care much for cooking, but I rather like the cleaning up," Johnson says. Not since the recession of the late '60s has he had the servants that made his entertainments (often of students he taught at Yale) so easy and elegant. Now he's down to a caretaker, a gardener and a cleaning woman.

The high ceiling combined with glass walls, distant views and reflections distort your perception so you have no real concept of the house's height or width. It's as though you were floating through the woods in a square bubbie.

Sitting in a Barcelona chair and looking out at the trees, the hills, the green grass with its wildflowers, the soft nature against the hard house, is an indelible experience, if you care more for houses than gold or diamonds or strawberry tarts. Peace sifts down as the sun warms the back of the neck before going on to sparkle in the table top. The strong sensation can be played again in the mind when the world is too heavy. Even the widely published pohotographs of the house have left deep marks on many.

The oldest building on the estate is the introverted guesthouse with its three porthole windows facing away from the main house. Since it was finished first, in 1949, Johnson lived there while he presided over the completion of the glass house. Inside are a luxurious bedroom with a series of sybaritic arches forming a wood canopy, a small TV room and two baths.

In 1962, Johnson seceded from Mies and his fellow Bauhausians who had been introduced to the United States by Johnson's definitive book (with Henry Russell Hitchcock), "The International Style." Johnson's manifesto was a concrete pavilion - a series of arches or a folly, if you will - he designed for the pond.

The playhouse is just tall enough to sit in without bumping your head, but through the tricks of perspective, it looks full-sized from the house. It is an architectural theater of the absurd, a thumb-your-nose-at-the-grownups type of building.As Johnson puts it "the mind stays at 30."

In 1965, when he began to seriously collect paintings for himself, with the advice of his friend, David Whitney, a museum consultant, he built an underground, dirt-bermed painting gallery into the hill to the north of the house. Facing its pi-shaped dark red sandstone entry, you think of Mayan temples. Johnson says Egyptian.

The ingenious building is a series of circles: 16-, and 12-and 8-feet wide, all 13 feet high. Each has a carousel with tracks holding panels that swing around to show 50 paintings of Frank Stella, or Andy Warhol or any of a dozen others. Because each of the carousels swings independently, there are endless combinations to be seen in the central viewing space with its leather stools. "People forget I'm a functional modern architect," Johnson says.

"I don't come here too much anymore," Johnson syas. It's nicer to show it to someone." The painting gallery also has a small kitchen and bath. He keeps wine here because, being underground, it says at a constant 55 degrees.

In 1970, he built a sculpture gallery he describes as two rectangles, one set upon the other at an angle. Johnson says "you can't draw or photograph" its geometry. he thinks it may be the "most original, the freest of all the structures."

Its solid brick walls have no windows but the roof is all glass, light tubes and metal frame. The gallery has six levels, reached through a ceremonial stair - all except the lowest level is visible from the top.

The room calls for ceremonies and celebrations. You can see great pageants moving up and down the steps (preferably with spear-carriers). Johnson suggests "it would make a great church or theater - Can't you see Shakespeare here? . . . That level would be fine for the balcony scene . . . I've even thought it would make a grand house . . . That lower level could be the indoor swimming pool."

In the gallery are the sculptures of Mark diSuvero, Robert Rauschenberg, and Donald Judd. (More large pieces are scattered throughout the grounds.)

Now the bulldozers are clearing the ground for the newest of the Johnson buildings, a concrete fantasy structure with soaring spires to serve him as a study.

Johnson, thinking seriously about how to protect his masterpiece when he's no longer around, once planned to give it all to the Museum of Modern Art in New York City. He is one of the two or three greatest donors to MOMA - several million dollars in paintings. He not only founded its architecture department, but paid his own and his staff's salaries. He served as the museum's architect-in-residence for 40-odd years (designing the museum's offices, its sculpture garden and its east wing).

A year or so ago, MOMA decided to build an apartment building over museum and did not ask Johnson to design it, apparently because of a possible conflict of interest since Johnson was on the board. "I was mad at the Modern," he says. Besides, after he thought about it, he was not convinced that MOMA had a real use for the house.

So he has rewritten his will to leave the estate to the National Trust for Historic Preservation. Though, he says, "if I were 81 and bedridden, I might change my mind."

Johnson already has made the first payment into a generous endowment. "It's a very expensive house to keep up," he syas. The bill for the floor radiant heating in the glass house alone is about $1,000 in the coldest months. During the great architectural slump a few years back he had to close the house for two winters. At the time, according to fellow architects, he sold his Alcoa stock (the foundation of his fortune) to keep his architectural office open and to finish his sculpture gallery.

The official announcement of the new beneficiary will be made at the convention of the American Institute of Architects May 21 in Dallas, when Johnson will receive the AIA's gold medal for a lifetime of achievement - his work as an architectural critic/historian and such notable buildings as the Fort Worth Water Garden, the Crystal Cathedral in Southern California (all with his architectural partner John Burgee), the New York State Theatre at Lincoln Center and the Seagram Building with Mies van der Rohe, as well as a number of houses. One of the grandest is the David Lloyd Kreeger house in Washington. In New York, he rents one he designed for Mrs. John D. Rockefeller III.

James Biddle, president of the National Trust, says he is especially pleased with Johnson's bequest, because the trust its interested in preserving properties of all periods, including our own. (The trust also owns the Pope-Leighey house by Frank Lloyd Wright on Woodlawn Plantation here.) In the meantime, the Johnson house is very much closed to the public.

There's no use turning up at the door unannounced. We had walked up the hill - Johnson putting on a black and white plaid shirt against the cold - and into the painting gallery, when we heard a commotion at the door - a woman stood there, yelling at Johnson, "I've never seen anything like that house in all my life. Can I come in and see it all. I've never seen anything like it. Nothing."

Johnson identified himself as the owner and courteously said the house was not open to the public. She continued to say she'd never seen the likes. Finally, Johnson suggested that she was trespassing, and only then did she leave.

The incident happens often though the house cannot be seen from the road and its drive is unobtrusive. Usually the gardender and the caretaker, who lives at the top of the hill, ward off intruders, and, of course, there are secret safety devices.

Johnson majored in philosophy, with a minor in Greek when he went to Harvard the first time. (The second time was when he went back for his architecture degree when he was in his mid-30s, after attaining a considerable reputation as an architecture historian and critic.) He still enjoys meditating on architecture as art, or as he puts it "form follows form."

Curled up on his Mies chaise, he talks about the speech he plans to write that afternoon (delivered when he received the Thomas Jefferson award last week from the University of Virginia). "Not only do you get $5,000," he says - "I'll buy a Stella with it for the Modern - but best of all is the candlelight dinner in Monticello.

"I think the wonderful thing about architecture today is its diversity," he said, adding that once he and other modern architects believed with Mies that one style would fit all. "His church at the Illinois Institute of Technology looks less like a church than his powerhouse nearby . . . but the aim now is toward making a house look like a house, a church a church, a factory a factory."

Johnson said easily understood symbols (spires, for instance) and the genius loci (the spirit of the place) are as important elements in the architectural equation as function and structure. "I suppose some people would fault me because all my buildings are different, none are in a single style. But I would be bored doing the same thing all the time.

"As Chairman Mao put it: Let 1,000 flowers bloom. As the Bible has it: The house of our Lord has many mansions."