Two photographs illustrating an article on "The Treasure Houses of Britain" in last Sunday's Washington Post Magazine were accompanied by erroneous caption information. A photograph said to be of the Painted Hall at Chatsworth is actually of the Blue Drawing Room at Woburn Abbey. A wall-hanging in the background of a photograph of a 17th-century-style chimney piece should have been identified as a Soho tapestry from Grimsthorpe.

ALL EXHIBITIONS have a history. But the history of "The Treasure Houses of Britain: Five Hundred Years of Private Patronage and Art Collecting," opening next Sunday at the National Gallery, turned out to be more complicated -- even perilous -- than most.

Gallery Director J. Carter Brown was nearly killed last year when his car was hit broadside as he drove through Yorkshire to Castle Howard, and he spent months moving around on a motorized cart while his broken hip, pelvis and four ribs mended. Earlier, gallery design chief Gaillard Ravenel and his assistant chief Mark Leit found themselves being peppered with shot one evening as they strolled the grounds of Blenheim Palace. The duke of Marlborough was out hunting pheasant, and didn't know they were there.

None doubt the worthiness of the outcome. "In all humility," Ravenel says, "it is the most fabulous exhibition that has ever been done in any museum anywhere in the world."

It is also the largest show ever undertaken by the gallery. Ravenel, Leithauser and the exhibition's British curator Gervase Jackson-Stops, all performing under the magic baton of the daring Carter Brown, have transformed the top two floors of the gallery's East Building into a one-stop tour of 220 country houses dating from 1485 to the present.

No rustic weekend cottages, the "country houses" under scrutiny here are immense stone palaces where Britain's rich, powerful landowners have been riding to hounds, bagging pheasant and, by accident of primogeniture, getting richer since the days of Henry VIII. Though time, taxes, the rise of the middle class and high death duties have finished off many a country house, some 800 owners hang on. As a group, they own the greatest lode of European Old Master paintings and decorative art still in private hands. The owners of Britain's country houses would like to keep it that way: thus their willingness to lend such treasures to this exhibition, which they hope will raise both awareness of the threatened British country house and the numbers of paying visitors at their gates.

THE SHOW at the National Gallery is no ordinary parade of greatest hits from the stately homes of England. It is a time machine, consisting of 17 imaginary period rooms that offer a leisurely ramble through 500 years, tracing, through different architectural styles, decor and works of art, the changing tastes and collecting habits of the British landed gentry.

The 700 objects exhibited are worth a fortune -- 250 million English pounds -- and include paintings by Holbein, Rembrandt and Titian; sculpture by Praxiteles, Bernini and Henry Moore; furniture by Adam and Chippendale; and lavish displays of silver, porcelain and tapestries by the leading craftsmen of their time. The show also cost a fortune to put together: roughly $3.5 million, $1.5 million donated by the Ford Motor Co., the rest from the U.S. Treasury.

Most agree: Only the National Gallery under Carter Brown, with his energy and clout, could have pulled it off, and everyone involved pats everyone else on the back. "Nobody but Carter would have conceived of doing something on such a scale," says Ravenel.

"It could not have been done without Gil Ravenel and Mark Leithauser, who have totally transformed this relentlessly modern I.M. Pei building," says Jackson-Stops.

Carter Brown says it couldn't have been done without Julian Andrews and the British Council. "They sweated blood in physically bringing it all together."

THE AIR SHUTTLE between Washington and London began in earnest three years ago, with Brown, Ravenel, Leithauser, Jackson-Stops and various others dashing back and forth on a regular basis, wooing, dunning and dining with various dukes, marquesses and other assorted Brits to firm up loans.

Special help in wooing came from Jackson-Stops, architectural adviser to Britain's National Trust, who had already written guidebooks to 30 of the houses. He worked out of a one-bedroom basement flat on London's Draycott Street in Chelsea, a command post set up by the National Gallery.

Further help in securing loans came from one of Jackson-Stops' assistants, Anne Chandos-Pole (pronounced Pool), who grew up in a country house herself -- Radburne Hall, built for an ancestor in the early 18th century. Her parents, whose house is not open to the public, are anonymous lenders to the show.

"Growing up in a country house is much like growing up anywhere else," she says, "but it makes you appreciate quality. You're brought up with your eyes tuned in." Chandos- Pole collects Victorian watercolors. Her parents, she says, do not collect. "The money goes into the roof. You've got to work very hard to keep up."

"The people who own these houses are wonderful," says Ravenel. "They are among the most friendly and generous people I've ever met working anywhere." In their travels around England, Scotland and Wales, Ravenel, Leithauser and Jackson-Stops seemed most to enjoy Lady Cholmondeley (pronounced Chumley), the 93-year-old doyenne of British country householders, and happily recalled that upon arriving at her country house too late for tea, they were served a supper of oyster stew.

Lady Spencer, stepmother of Diana, princess of Wales, turned out to be the biggest disappointment: "Of all the country house owners I've asked, I haven't had one refusal except for her," says Jackson-Stops, "which is pretty rich considering the fact that the house belongs to her husband."

Other than that, the rosy-cheeked curator got what he wanted, including loans from four royal country houses -- Balmoral, Sandringham and Osborne -- and Highgrove Park, the country house of the prince and princess of Wales.

Despite the warm receptions, the "travel wasn't always as glamorous as it sounds," says Leithauser. " . . . the fun wore off fast; it was so cold and damp, and gloomy.

"Some of these places are filled with cobwebs and weirdness." He recalls a spooky night spent in a Jacobean house whose owner seemed to enjoy the smell of decaying linen. "He asked me if I'd like to see the room where they took people to die, and there it was, the Death Room, with daguerrotypes of people who'd died there, and stationery with black edges. The cabinets were full of sickroom aids, things like early copper vaporizers."

No one has yet counted the number of cross-Atlantic trips staffers made, but there were hundreds, and there would have been more without the computer. National Gallery exhibitions assistant Cameran Greer was sent to London to train the small staff to use the computer that kept all parties on both sides of the Atlantic instantly apprised of the status of loans, catalogue entries and other matters.

"It surely couldn't have been done without a computer,' says D. Dodge Thompson, the gallery's chief of exhibition programs. There was also the matter of coordinating the 700 updated entries for the catalogue, published jointly with the Yale University Press, which were written by dozens of different experts, such as the keeper of the Tower of London, an expert on armor, and the keeper of the Queen's Pictures -- "all people you obviously can't call up and tell them to get on the stick," Thompson says.

One snowy day last February, when the computer wasn't working, the scene at the London flat seemed far from the glamor of jet-set travel and country houses. There was no heat, no refrigerator and no hot water for tea. "I do miss my tea," said Jackson-Stops, who was slogging away in the back room, writing not only the catalogue essay, but another entire book (with photographs by Washington lawyer James Pipkin, titled The English Country House: A Grand Tour, just published by Weidenfeld & Nicolson in London for the National Trust). Greer finally figured out how to get the heat on by turning a valve with a pair of pliers.

LATE THIS SUMMER, when the crowds of country house visitors in Britain had thinned, a fleet of lorries set out at last, crisscrossing the country, picking up the art and taking it to London warehouses. There the pieces were packed in custom-made cases and airlifted to Washington, three shipments a week for three months. Like plutonium, the works were shipped by many routes, their movements shrouded in secrecy.

"Fortunately, the British are good at logistics," Brown says, comparing the operation to the invasion of Normandy.

The other crucial matter taken on by Julian Andrews and the British Council was insurance. The British and American government covered the risk. Private insurance could have cost as much as $2 million or more, says a National Gallery insurer. Britain is bearing the brunt: American liability is limited by law to $50 million.

Incredibly, when all had arrived in Washington un- scathed, there was only one gaffe. Jackson-Stops opened one newly arrived shipment and wailed, "Good Lord, they've sent a reproduction!" It was swiftly returned and replaced with the original.

EVERY TIME Leithauser, Ravenel and Jackson- Stops went to Britain, they took with them the same roll of master drawings on erasable frosted Mylar, all made by Leithauser, the only one who could draw. The drawings were used to visualize what the 17 proposed rooms would look like.

"After looking at various houses, the drawings would change dramatically," Leithauser says. "We would go over every single one, every single wall, every single object, and completely change the shape, the height, the contents of the room, over and over." Leithauser's drawings guided crews of engineers and craftsmen in the transformation of the East Building.

Jackson-Stops often took the roll of drawings with him to persuade country house owners of the importance of their loans. "Some," he says, "were rather astonished to see their treasures already drawn in, hanging on our walls. But they all agreed because they realized this was the country house exhibition of their lifetime, and possibly the last ever."

Except Lady Spencer, of course. "We eventually matched what she had at Althorp, which is everything . . . paintings, furniture, silver, sculpture," Jackson- Stops says. "But it's sad to think that one of the major houses of England, which needs the publicity, is not included in the show."

Perhaps Lady Spencer was not aware: Their royal highnesses the prince and princess of Wales are the patrons of the exhibition, and to prove that they care, they are coming to Washington for a round otering festivities on Nov. 9, following the opening. So are 200 other country house owners and lenders. Lady Spencer is not expected to attend.