Insofar as anything human can be perfect, last night's reception and supper at the National Gallery was perfect, honoring the British lenders of art treasures from their country houses for months-long display in Washington.

Guests had the astonishing opportunity of wandering two full hours in the 18 rooms displaying pictures, furniture, domestic wares, tapestries, sculpture and gilded silver in a show that is not likely ever to be called anything less than "incredibly brilliant," as Lord Gibson of the British National Trust put it.

A beautiful young woman, Lady Leigh, showed up in an elaborate silk dress with a good truckload of material at the back -- a dress belonging to an ancestor shown in one of the show's paintings, "The Grosvenor Family."

"The thing you don't realize at first," she said, "is that a dress like this rules your life. You can't lift your arms, you can't make any sudden or abrupt movements, you must be cautious about sitting down and you need two maids to get you in and out of it."

It's a dress that makes a woman a lady whether she will or no, and the question arose whether all women should have such a dress just for the hell of it.

"I don't think there is much demand, now," she said. "It is perhaps too late."

Hardly anybody had ever seen a sculpture of Praxiteles, but there was a head of Aphrodite from Petworth attributed to him. Never mind whether you liked it or not. Wow.

David Brinkley, television newsman, would press one to name the best things in the show, but was bullied into giving his own preferences first:

"First, the Stubbs picture of the mare and her foals. I've never seen such a beautiful painting of horses, and I've seen my share of them. Then the silver bathtub, and that incredible state bed ordered for a queen but never unpacked until just recently, so it looks brand new. I told Sue (Mrs. Brinkley) she could jump out of the tub and into the bed."

The tub in question is a silver cistern for ice to cool wine bottles and comes from the Burghley House Collection. It weighs nearly 4,000 ounces of solid silver and has little lions holding on for dear life with their paws on the rim. It is the most flawless vessel anybody ever saw for bathing a basset hound, retriever or (as Brinkley suggested) a rambunctious collie. Surely over the centuries it has been used surreptitiously for the purpose.

Dinner began with a fanfare of four trumpets high in the gallery and guests settled in at tables for 10, laid with glazed chintz cloths like a country sofa, covered with big roses and tulips in soft colors, and each table centered with a classic urn stuffed with greenery, all very Augustan. No flowers to speak of, but they probably wanted to avoid chrysanthemums.

Supper included crab in a sauce -- you would not expect to rassle whole ones on butcher paper, so guests wound up getting considerable to eat -- and medallions of venison. A Britisher asked if it came from Germany, as if the entire East Coast were not overrun with deer.

One might find to his right Lady Wake, whose family have lived since roughly the Flood in Northamptonshire, and who lent a red book (as these designs are called) of Humphrey Repton. He arrived at their place a century and a half ago with his clever book showing the estate as it then existed, with pull-outs showing how he could improve the landscape. In his day he chopped down God's own plenty of trees to suit his designs, and at this house was thanked but allowed to leave, and the great trees still stand. Except, of course, the tremendous English elms that died of disease "imported from you," as Sir Hereward Wake put it.

"Well, we must have got it from the Dutch," a loyal American retorted.

A Danish-type beauty (her family were from Denmark) was Lady Tollemache, from East Anglia, where there are no wretched mountains and where the sky can be seen 360 degrees. She lent one of two copies now extant of a book on the orpharium. This is not a guide to orphan care, but a book concerning an instrument like the lute. At her house they have perhaps the only such instrument now remaining in the world, she said, a gift of the great Tudor Queen Elizabeth to the family when she visited them in the 1500s.

"I do rather like sleeping in Queen Elizabeth's bed," she said, though she hinted, quite delicately, mind you, that the family fortunes never quite recovered from the cost of entertaining majesty.

Lord Charteris, chairman of the Committee of Honor for the show, thanked the Ford Motor Co. for bearing so much of the expense involved and gratified the colonials of Washington by saying he doubted such a show could be mounted so brilliantly in any other museum in the world, and neat graceful words were spoken by Franklin Murphy, the gallery's chairman; Donald Petersen, Ford corporation chairman; and J. Carter Brown, gallery director, who saluted his staff to a fare-thee-well, as well he might.

Lady Wake was much baffled to think of the name of the American sweetgum tree, now coloring brilliantly hereabouts. "Liquidambar," she cried suddenly during a temporary silence. And Liquidambar said we all.