LORRAINE COOPER is one of the two or three Washington grande dames left, now that Alice Roosevelt Longworth and Virginia Murray Bacon are dead. Lorraine and John Sherman Cooper's elegant Georgetown home is among the last of the great salons. And Lorraine Cooper, at 73, still seems as if she were invented by Noel Coward.

Mrs. Cooper has made a profession of living with great elegance: in an apartment in New York, as a socialite divorcee in Georgetown, then as the wife of the senior Kentucky senator and, as "principal wife" (the Foreign Service term) at American embassies in New Delhi and East Berlin, when the former senator was an ambassador. Now her husband is a lawyer, but she still gives her annual spring party for the Senate, a great occasion no one would willingly miss, and her chic dinner parties for 24. President and Mrs. John F. Kennedy came to one on their first night out of the White House after the inauguration.

Lorraine Cooper is a remarkably stylish woman with short hair framing a strong face and interesting bones.

"Cecil Beaton once photographed me," she said. "He said, 'Your face breaks the camera. You should only let me photograph you.' It took him 20 minutes for one picture, he tried all sorts of positions, but the picture was glorious. I've never had one so wonderful again."

She was among the first in Washington to wear the mini (with a neckline cut to there ) and the midi. But with her 5-foot-6-inch height and size-eight figure, she has always been able to wear what she liked. W publication the other day saluted Mrs. Cooper for her "staying power."

"I decided as a schoolgirl in Florence to choose boys instead of cakes," she once said. She lived in Italy after her mother, the former Mrs. Robert Rowan, married the Prince Orsini.

She likes Dior clothes, she once said, because "that's the only place that gives me credit. I believe in deficit spending. I send along a small check every month."

The other day Mrs. Cooper took us through her house, a star of this year's Georgetown House Tour, that annual voyeur's holiday. The four-story, red brick house dates from 1798-1804, when a prosperous merchant built it with a captain's walk atop the roof so he could see if his goods were coming in to port. Lorraine Cooper bought it in 1953, when she came to Washington. Two years later she and Cooper were married, just before he was appointed ambassador to India.

Though her house is run to a scale to which few people would aspire, she's not above saving a penny when it can be done without sacrificing appearances. "Anything for show," she explained. "Or as a friend of mine once put it: Lorraine, you like cheap luxury."

The Cooper luxury looks anything but cheap: crystal candelabras, rare Oriental procelain, Indian treasures, modern paintings, leather-bound books, elaborately draped tall windows. Yet nothing calls out for attention or speaks too loudly.

Her best buy probably came the time she saved up, bit by bit, $1,000 to buy art. "Salvador Dali came to visit," she said. "I told him how I longed for his Catalan landscapes. I asked him if it was possible to buy two for the money I had. His wife nodded.

"Some time later he wrote me and said they were ready. He was not at his studio when I went, but I took the paintings and left my $1,000 and wrote a big gush of a note. Later a friend told me, 'It's a good thing you have lovely adjectives and wrote such a nice note. Dali thought you meant $1,000 each ." She paid $100 and $200 for her Raoul Dufy watercolors.

About this time of the year, Mrs. Cooper is busy taking down the heavy winter overcurtains and slipcovers in her parlors and substituting white pique, linen and fern-patterned fabric. The goat-fur rug comes up and the straw rugs go down and the snow red fox from China comes off the library sofa. s

It takes her staff of three or so and two outside people two days to change her house's calendar from winter to summer.

The sofas are deep and comfortable. Small footstools rest the feet of those weary of walking the corridors of power, or serve to be pulled up by worshipful juniors anxious to sit at the feet of the wise. Yet it's not a period piece. Over the fireplace in the drawing room are difficult abstract paintings by Olipsi, mirrored by a late 19th-century gilded mirror. A wicker sofa and two chairs are painted black. Mrs. Cooper paid $25 for them 25 years ago.

In the drawing room, the winter upholstery on the overcurtains, easy chair and sofa are flowered with brocade valances. Two small tables and a settee are covered with a rosy Marimekko print. A large porcelain Indian elephant serves as a cigarette table. Elephants are embroidered on the napkins, which came with the coffee and cookies, a reminder more of her husband's political affiliations than of India. Two fanciful gilded consoles stand on either side of the library door. A tooled Spanish leather screen stands by the fire.

The library, in the Georgetown rowhouse fashion, is a twin room behind the drawing room.The walls are covered with books. "I'd love to cover them all in felt so they would match," she said. The settees are slipcovered with a blue and white fabric -- "bought for $2.50 a yard, but some years ago," she said.

Long windows, covered with a lined, stuffed and quilted fabric for insulation, open onto the south gallery. The glory of the house are the loggias or porches on the three principal floors, facing south so they can be used on sunny days all year. For several years, Mrs. Cooper covered the porches with clear builder's plastic and curtains during the winter, so she could spill her receptions out on them. But now, she said, she can't find the right size of plastic.

The dining room and kitchen are downstairs. "It's a bad room; I had to trick it as much as possible," Mrs. Cooper said. "The ceiling is low and noisy. So I lined it with fabric, hung from rods like curtains." The curtains are pulled back at the French doors, which open onto the garden.

Before they went to Berlin, Mrs. Cooper rehung the room with a dark brown for winter. "But some of it wore out, so I made new curtains for John's room of what was left."

The garden, deep by Georgetown standards, is the scene of the Coopers' annual garden party for the Senate. When he was senator, the garden was where Mrs. Cooper dispensed "lemonade and brownies" for hordes of girl scouts.

"I remember a neighbor once called and said, 'Lorraine, do your guests always arrive in buses?' Of course, I knew what she meant. The buses do have such bad breath."

Being a hostess in Georgetown isn't always easy. Mrs. Cooper recalled a party she gave with a rock band for her nieces. "Of course, I had written all the neighbors to warn them, as we do in Georgetown. But the police arrived midway in the party with a woman whose baby was awakened."

The Cooper house looks like spring for most of the year. Mrs. Cooper keeps the Chinese Export porcelain and small Indian ceramic elephants full of flowers. "That forsythia in the urns is rather tired, I'm afraid. I talked with Michael [her longtime English butler, as good-looking as a movie star] about getting some more. There's a great bush of it just down the street, but we agreed you'd have to wait until after dark.

"It's best to go to the market, early in the morning," she said. "You can buy armsful very cheap. Now that I don't have a car, I buy them on the streetcorners of Georgetown. It costs too much to buy as many as I like from the florists."

In East Berlin, Mrs. Cooper said, she bought flowers at the Berlin Wall. "No one could imagine anyone wanting so many flowers. Sometimes I used masses of tulips, all white and green, or purple and red hydrangeas. I bought miniature orange trees and put them on the stair landing. During the summer, I put the orange trees by the door and people would come especially to see them. In North Germany, citrus isn't so often seen."

But not all ideas translate so well. One night for a party, she filled the house with candles and turned off the electric lights. "One man told me, 'It is like in the time of Frederick the Great.' Only after a few minutes did I realize he equated candles with a lack of energy, hard times, poor countries."

In her Georgetown house, sometimes the pleasant scent comes not from candles or flowers, but from perfumed oil, saturating small pads placed on the tops of lamps.

Mrs. Cooper hated the house the United States government bought for the East German embassy. "It was gruesome. A waste of money," she said, though she never lived in it. She and her husband lived in a block of diplomatic houses because the new house bought by the United States wasn't finished.

"Lorraine is totally original but nothing she does is formless. Nor is it rigid. She envelops form and rules in ease, warmth and informality. The boundries are not obtrusive."

"The house we had was not depressing because anything we did to it made it look so much better. I draped the walls in cherry damask, for instance."

Mrs. Cooper obviously enjoyed being a diplomat's wife. She likes to say that when they first went to India, "Evangeline [Mrs. David] Bruce gave me a crash course in diplomacy."

Evageline Bruce has said of her own knowledge, "I was dipped in diplomacy from birth.

Mrs. Cooper said that diplomacy is like bridge."Either you do by the rules or you don't play. I always made calls, for instance. I think a 20-minute formal call gives you a real knowledge of the person and helps you so much when your husband has to deal with her husband. Often you can know them well and when they spill the beans you can tell your husband what they told you."

Mrs. Cooper herself was careful about accidental spills. "In East Germany, we always had music on the record player to help scrabble the wiretaps, or left the refrigerator door open (so the motor would run and mask the talk). I always presumed the telephone was tapped when we were abroad. But then I always thought John's office was tapped when he was a senator. I knew one high offical who asked to have his telephone tapped. He thought it protected him."

Mrs. Cooper, for all her great presence, admits she didn't always feel so confident. "The first time I went to the Senate Wives meeting, I jabbed a hat pin into Mrs. [Dwight] Eisenhower's shoulder. I could just see the headlines: 'Senator's Wife Murders President's Wife With a Hat Pin.'"

Like most wives of retired senators, Mrs. Cooper still goes to the Tuesday luncheons of the wives. "At my age, you could get into a rut if you don't go out. I feel I can learn from the new ones."

In a day when people and houses are casual and often slipshod, Lorraine Cooper still stands for the appearance of ease and elegance, the observance of protocol and the knowledge of when to be outrageous.