It was VIP preview day at the National Gallery of Art and J. Carter Brown, known to friends and acquaintances as Carter, or in the week of English invasion, Cawtuh, glided down the Jacobean Long Gallery, a painstaking evocation, down to the leaded glass windows and the fake cracks in the fake walls, of a great hall in an English country house.

The hall was hopping with aristocrats, lenders and pretenders, lords, ladies and a sprinkling of unhyphenated hoi polloi. A courtier approached, in the form of Jerome Zipkin, friend to the first lady, confidant and escort of American socialites from coast to coast.

"Cawtuh," Zipkin said rapturously as he tugged on Brown's elbow, "I'm losing my mind! I'm losing my mind! I'm absolutely staggered!"

As Zipkin fell back to pay homage to a king-size oil portrait of Frances Howard, Countess of Hereford, Brown was buttonholed by a clump of Englishmen, one of them stalky and dressed in a suit as fine and gray as a dove's back: The Lord Gibson, chairman of Britain's National Trust and a member of the exhibition's Committee of Honour (which the gallery is spelling with a "u" these days).

"Do yaw remember that first meeting in London?" Lord Gibson mumbled elegantly. "I do, I do," Brown murmured back. "You've all been so supportive." Then he was off again, to link up with the top executives of Ford Motor Co., donor of most of the estimated $3 million it's taken to put together the "Treasure Houses of Britain" show.

The group stopped before a Van Dyck portrait of Lords John and Bernard Stuart, two young brothers swathed in silk and self-absorption. One of the Ford execs observed that the brothers' stirrups have leather toes, "like slippers," the man said, proud of himself for noticing but a little tentative just the same. "So they do!" Brown replied warmly, all grace and surprise. "You're absolutely right!"

On his way to the elevator, Brown suddenly swooped sideways, stopping to inspect the small type on a piece of paper taped to the wall. A temporary label. "There's a typo," he announced. "It's Keswick. This says Kenswick."

And finally, waiting by the elevator, he paused before a wall-sized blow-up of a black-and-white photograph. "This is the last Duchess of Buckingham, at Stowe, which was converted to a school I attended one year," he said. "It has the most beautiful gardens by Capability Brown." Lancelot Brown was an 18th-century landscape architect so nicknamed for his way of referring to the "capabilities" of the grounds he was hired to improve.

"No relation," said J. Carter Brown.

Stroking, smiling, bowing to the scraping of the social violins, J. Carter Brown, director of the National Gallery of Art, may be in his finest hour, and arguably his most public, since the opening of the gallery's East Building in 1978.

"The Treasure Houses of Britain," which opened Sunday, is his show. It was his idea, he nurtured it, found money for it, courted the lenders (with the help of Gervase Jackson-Stops, curator of the exhibition and architectural adviser to the National Trust) and found more money again. It was he who snared its royal patrons, Their Royal Highnesses, the prince and princess of Wales. And if that weren't enough, he very nearly gave his life for the show, in an auto accident last year on the road between Harewood and Castle Howard. More than any gallery show in his 16-year tenure as director, this one is his baby, silver spoon and all.

"He's had a tremendous interest in this one," said a longtime gallery staffer. "If you'd seen him walk through 'Art of the Pacific Islands,' he probably wouldn't have noticed if the label had said Papua New Guinea or the Sepik River."

Critics and connoisseurs have been swooning over the show for months, though there have been a few raps from reviewers troubled by the reverential treatment of the country-house set.

And when the estimated 1 million visitors (700 visitors an hour at full throttle) traipse through the show between now and March 16, it will be Carter Brown's voice they hear on their Acoustiguides, the burnished Yankee drawl, pitching and diving like a yawl off Newport, welcoming them with an expansive, "Hello, I'm Carter Brown . . ."

The show's roots are in Brown's Rhode Island upbringing, his unabashed Anglophilia, his conviction that the great houses are great repositories and records of British culture. "If he says 'vessels of civilization' one more time, I'll scream," a gallery employe joked recently.

"I was puzzled," Brown said recently, settled in his office down the end of a long, hushed corridor in the East Building. "Americans who travel generally didn't seem to know about the houses, and would assume that since the great museums in America are almost all in the cities, the city is the place to go when you visit Europe . . . But there are these other great places way out in the country, by definition in the country.

"The part that fascinates me most is why they collected in the 18th century. They saw themselves as descendants, spiritually, if not genealogically, of the Romans, who in a sense saw themselves spiritually, if not genealogically, descendants of the Greeks. And we in our way, particularly in this city of Washington, with all this classical architecture around us, we are the inheritors of this same tradition. So that it is, in a way, a seamless web."

Once exhibition plans were under way, Brown made his overtures to Prince Charles over dessert at the British Embassy a few years back.

"I think they saw the wonderful opportunity it represents for Britain, in terms of calling attention to this heritage and attracting visitors, so that it seemed almost a patriotic thing to do," Brown said.

"It seemed such a perfect fit. They were just furnishing their own country house and obviously interested in the country house idea . . . It was so helpful to have the sense of youth and energy of people interested in this cause . . .

"I mean an alternative would have been the marvelous Queen Mother, who has been such a patroness of country houses all her life and of art collecting. Whether or not she would have been up to making the trip, I don't know. She seems to be full of beans, apparently . . ."

The royal nod sent the roller-derby queens of high society rocketing off in search of invitations. Brown is reportedly one of the few mortals with an invitation to the Social Trinity -- the White House dinner, the British Embassy dinner and the dinner at the National Gallery -- although he declines to say so. "I'm sure those guest lists will be announced at the appropriate time."

The party line on the socializing, of course, is that it's too, too tacky to talk about. Those who know him wouldn't expect Carter Brown to be flustered by a royal visit. And there are few Americans better equipped to play host.

"Carter's particular grace is that he has all the style and the background to pass for royalty in this country," said Michael Botwinick, director of the Corcoran Gallery of Art. "But his charm is he doesn't conduct his life that way."

Only his Filofax knows for sure, but whether he does or doesn't, Brown's been training for this visit all his life. He was born in Providence, R.I., into a family that reaches back into the 17th century, when they reportedly made their money in shipbuilding, the molasses trade and real estate. His father, a descendant of the founder of Rhode Island, served as undersecretary of the Navy in the Truman administration.

Brown attended Groton, and sailed in the summer with John Walker, then director of the National Gallery. He graduated Phi Beta Kappa and summa cum laude from Harvard. He was the last student of art historian Bernard Berenson at I Tatti in Florence. He has a Harvard MBA, a master's from New York University's Institute of Fine Arts and an LLD from Brown University.

His first marriage was brief, to a second cousin of Paul Mellon. His present wife is Pamela Braga Drexel, the daughter of a prominent New Jersey family whom he married in 1976 in Westminster Abbey, an occasion he obligingly describes like this:

"I made a courtesy call on the dean of Westminster Abbey, and he said he wouldn't hear of our being married anywhere else but in the Henry the Seventh Chapel, which is one of the most beautiful architectural jewels that exist, that incredible ceiling that it has . . ."

As director, his name has been inextricably linked with that of gallery benefactor Paul Mellon, and under their enthusiastic stewardship the museum has flourished.

In a job that requires social as well as scholarly skills, Brown, whom acquaintances describe as rather shy by nature, is a master at chatting up the right noble so-and-sos.

"I realized it last night when I just couldn't force myself to get into my penguin suit again," said Mark Leithauser, the gallery's deputy chief of design and installation. "That is sort of what he does. It's like being a rock star. I saw it this time, he was sort of entertaining Lady Plushbottom and she was loving it.

"In England, we'd all be trudging through a house and he was just so charming. He would manage to walk through and find something good to say about everything."

At 51, the years and miles have exposed the aristocratic architecture of his face, its shrewdness, avidity and the jeweler's eye. When he is smiling, he lights up with a boyish exuberance that can quickly turn to distracted frost.

Associates say he can be remote, even aloof. "Private" is the way he is most often described. And very competitive.

There has been talk this season that the gallery has stolen the thunder from the Metropolitan Museum of Art's mammoth show, "Liechtenstein: The Princely Collections." There is a longstanding rivalry between the two museums, exacerbated by the gallery's insistence that any traveling exhibition to be shown at the gallery must open in Washington.

"I think it's a dazzling show," Brown said of the Met's blockbuster, adding, "It was offered to us first. And we would have loved to have it, but we couldn't schedule it."

The British, he said, had expressed interest in a show that would showcase British culture, but had modern art in mind. Brown's idea was different, an idea that he'd been toying with for some time.

"I look back through my travel records," he says, "and the fact that I'd stayed with the Duke and Duchess of Devonshire at Chatsworth only a few months before must have gotten things going. But my memories of English country houses go way back.

"I have a British family, or cousins, that have been terribly kind to me over the years, and I used to go there as a kid with my parents and pay family calls on Lord Camoys, and his son, the present Lord Camoys, is a very good friend, and I'm godfather of his son and heir, and they have a country house that's been lived in longer than any other in England, called Stonor. And so I've been fascinated by the country house idea, I guess, ever since I was a child."

"He loves the country house the way we all do," said Leithauser. "The tack room and the stable and the umbrella stand with 300 years of walking sticks."

Or as Brown said, fondly, "There is this tremendous contrast between the kind of agrarian life that was led there and the high civilization of the life style inside the houses, even within a 24-hour period. Because the British love the country and they slog around in their Wellington boots and they get all muddy and they love to get wet and cold and go fox hunting or shooting or just tromp around in their fields, and then in the evening they're in black tie and eating off this fabulous china, wonderful tables with the silver gleaming in the candlelight, and it's just a total transformation."

He did not know most of the lenders, nor had he visited most of the 200-plus houses. "I'd stayed with a few of them and my wife also knew a few; she used to spend every summer in Scotland and her parents used to invite people to go grouse shooting and so forth. I went to school in England for a year, but I must say that the vast majority of these lenders I hadn't met . . . It's such a vast universe. So many people."

The show's curatorial and design team did the Atlantic shuffle dozens of times, but Brown's travels were cut short during an early trip. Driving with his wife, Pamela, to Castle Howard after an afternoon of inspecting Chippendale furniture with the Earl of Harewood, Brown pulled out onto the highway from a side road but looked the wrong way.

Brown broke his hip, his pelvis and four ribs. His wife fared a bit better. "She was on the other side," Brown said, "and luckily she only bit through her tongue. She had a piece of it dangling down. It had to be cut off at the hospital and thrown in the wastebasket, but it grew back in three weeks.

"And then she was also very lucky, she had an old belt buckle and the windshield detached and came at her stomach but the corner of it hit her belt buckle and bounced off. So I feel very humble about the whole experience. It's a miracle that I'm here."

"It didn't stop Carter for a moment," says Jackson-Stops. "We went through all the plans and drawings on the hospital bed. He obviously was in some pain, but he never showed it."

The gallery's representation of British country life and its practitioners is unrelievedly rosy. The people are beautiful, the horses well fed. It is, wrote Robert Hughes in Time, a "portrait of a vanished order without revisionist detail . . . Surely by now an American museum can admit that a few of these paragons were educated brutes . . . or that their ideology of cultural property was underwritten by their power to hang men for poaching a stag or breaking down an ornamental shrub?"

For Brown the art historian, reconciling beautiful objects with harsh social history is a familiar exercise. "Well," he said, "one has this dimension in the whole history of art so we get rather used to it. I mean, the greatest disparity was the pharoahs. The objects in the Tut show were the result not just of oligarchy but a despotic monarchy . . . In the British system I think it's quite different . . . A lot of those titles came from people who only a short time before had been bright lawyers or smart businessmen or had been in favor with the court, people who had more or less gotten there by their own smarts."

As for the Downstairs folk who kept the Upstairs humming, the servant class whose virtual disappearance after World War II featured prominently in the decline of the baronial life, he takes a sunnier view.

"Working conditions were miserable, as they were all over the world," he said, "but the people who worked in these great estates probably had it better than the ones who had to work in the dark, satanic mills. And there was an aspect that doesn't show up much in the economic literature. That is the human aspect, a sense of pride in an almost extended family. I have seen it operating even to this day, there is a kind of rapport between house owner and a chief farmer . . . an intimacy within the bonds of respect.

"And because people didn't have this sense of competitiveness and sort of chip on the shoulder, that this should have been theirs if only they'd followed the Horatio Alger system, they could all relax and enjoy what they had."

What they had is what fascinates, and Brown thinks that goes deeper than stately rooms and servants.

"Sure there's a certain fantasy world, a 'Lifestyles of the Rich and Famous' voyeurism . . . The fact that these are British houses relates to our whole culture, our language, the literature we grew up with, and no matter where our roots are from . . . Our founding fathers lived in British country houses and now here we are, looking to our past the same as the British do, and we have it in common."

In the Waterloo Gallery, waiting to have his picture taken near Antonio Canova's sculpture "The Three Graces," Brown spied the Marquess of Tavistock, a handsome man in middle age, his blue blazer double-buttoned tightly across a neat little waist. His wife was draped in coat and trousers of rich, dusky plum.

"These are the people who own these works," Brown said quietly. Then he whirled on his polished heels and extended his arms in jubilant greeting. "Well, well," he said grandly, "ask the man who owns one!"