The taxi stops in front of the two huge bronze lions guarding a porte cochere on the Seine River side of the Louvre, France's national museum. A uniformed guard pushes open the heavy, double bronze doors embelished with a monogram of Napoleon I and directs guess up one flight where they are met by Helene de Margerie, wife of the director of museums of France, Emmanuel Jacquin de Magerie.

It is perhaps France's most exclusive address, for centuries the palace of kings and now a residence so exclusive that it would never occur to most people, even a Frenchman, that someone resides in the Louvre.

Built originally in the 13th century as a fortress against the English, and turned into a fortified palace a century later, the Louvre expanded to accommodate royalty and their acquisitions. In 1793, during the French Revolution, it was turned into a museum, and soon after it housed the flood of art works brought back to Paris from Napoleon's campaigns.

It is now one of the world's largest and most important art museums, displaying among its fabulous treasures the Winged Victory of Samothrace, the Mona Lisa, DaVinci's Venus de Milo and exceptional collections of Greek, Egyptian and Oriential antiquities. Degas and Manet spent hours and hours sketing there and Paul Cezanne, in a letter to Emile Bernard in 1905, wrote, "The Louvre is the book in which we learn to read."

The Margerie family, including daughter Laure, 20, and son Gilles, 21, now in military service in Germany, moved into Louvre in January 1975.

"In the evening when all is dark," says Laure de Margerie, a sculpture student at the Ecole duLouvre, "I just feel as if I were in a castle, because of the proportions of the rooms. When I stand at the windows, looking at the Seine, and I feel those huge rooms behind me, I can think I am in a big old castle."

Her mother, a geneticist who works on DNA reserch, agrees. "My friends couldn't believe that we would move in when we had such a beautiful apartment nearby," recalls Helene de Margerie cheerfully. "'Well, of course we are,' I told them. I am not so spoiled that I would pass up the opportunity of my life to live in the Louvre."

At the time he was appointed director of museums, Margerie (who is called "Bobby by his friends) had been head of the European desk of the Quai d'Orsay and prior to that, the very popular deputy chief of mission, the man, at the French embassy in Washington.

"It is not such an extraordinary change." says Margerie of the post, which is more administrative than curatorial. "My predecessor, who was here for 12 years, Jean Chatelain, was lawyer." Margerie was, in fact, said to be President Giscard d'Estaing's personal choice for the job. They had grown up in the same crowd, ahd been classmates at the pretigious Ecole Nationale d'Administration which produces the elite of the French civil service, and Giscard knew him as an art connoisseur as well as a skilled diplomat.

Touted as high on the list of potential ambassadors to the United States, Bobby de Margerie comments modestly. "It isn't my turn."

Several times each day he goes to his office via a private, hidden staircase through the Rubens gallery. If he has time to stop and look, the trip can take as much as two hours. If not, he races by in minutes.

He has a key that opens all the rooms in the Louvre. ("I'm not supposed to talk about my key," he says, laughing.) Sometimes in the evening, he and his wife will go to look at the paintings quietly, or if he has some work, he may suggest his wife come along.

"The key is one of the privileges of my job," he says, to permit me to get through the Louvre at any moment of the day or night, happily.

"I always thought how wonderful it would be to see a museum when the doors were closed to the public and to enjoy the paintings and other work of art quietly. Imagine Now that's my work."

When the Margeries moved into the Louvre apartment with its two high-ceiling, box-shaped drawing roons, its dining room facing on the Seine, and its kitchen and two bedrooms looking out on the Tuileries, the place was bare except for a mahogany dining room table and 10 chairs in the Jacob style.

On the Seine side, in spite of the remarkably high windows, the apartment, which faces north, is quite dark. Windows must be kept closed because of the heavy traffic on the express road below.

They had leased their flat on the Rue Bonaparte fuily furnished, so the Margeries started recouping pieces of furniture and art they had stored in the attics and garages of the houses of friends.

Madame de Margerie spins around pointing out the furniture style in the first drawing room. "Louis XIV, Charles X, Regency, Napoleon III, Louis XV," sahe recites quickly, greatly amused at the variety.

There is no less a mix in the art. Walls covered with as many as 20 paintings and drawings in a room include a painting her mother won at a lottery for charity in London, and two replicas of those in the Louvre.

"From a distance ours didn't look very differenct from those actually hanging in the galleries here," says Madame de Margerie. But when the Louvre versions were brought to the apartment for comparison, one was better, one worse than the ones they own.

The "bitter" was classic scene of a nursing mother surrounded by her children by 17th-century artist Blachard. "My friends alway say, 'How disgusting to have such a picture in the dining room,'" she comments, but she clearly enjoys it.

(There's no chance that they will exchange their painting to give the "better" one to the Louvre. Unlike other museums, France has a rule that no museum art may be sold or traded - the reason, perhaps, for the Louvre's encyclopedic collection.

"When something is in the Louvre it is there for good," explains Madame de Margerie. "The taste of the director at one time should never be regretted 20 years later.")

The apartment decor had been redone for their predecossor three years before the Margeries moved in and they found no reason to change it. An place in one drawing room that Helene de Margerie preferred to have painted in the 18th-century manner of "faux marble." With the approval of the head of architecture ("as a former palace of kings this is a historical monument, and needs such approcal," she points out) the fireplace was covered with varnish so it could easily be washed back to its natural state. It was painted by a skilled Louvre artist, one of the many craftsmen on the staff she is free to hire (and pay) when they are not working on exhibitions.

"It gives the room weight to have something dark and painted, says baseboards treated the same way. And she adds, "It's a great help in keeping the place clean."

with the never fully adequate budget for the Louvre now partially siphoned off for the Beaubourg, the cultural colossus dedicated to the late Georges Pompidou that opend in Paris this year, Bobby de Margerie is using his ten years as skilled diplomat and fine track record at refurbishing provincial museums to remedy this situation.

Palns for modernization of the Louvre have apparently been pushed aside. Galleries in the Louvre and Versailles have been closed because of insufficient funding for guards, a particular affront to Mergerie who would like to see the Louvre opened until 10 p.m. with expanded welcoming facilities to bring more working people into museum.

Currently he is researching a plan to use dogs to tighten security at the museum. They could, perhaps, stem the increasing art burglaries which, last December, included the theft from the Louvre of a diamond-encrused epee which had belonged to King Charles X.

Helene de Margerie, who after a si-year interim has started working again in an institute of radiobiology, did watercolors like most young girls of her time, but now is considering drawing. "Are you drawing?" asked sculptor Henry Moore, who visited the apartment recently whose works are being exhibited in the Tuileries this month.

Glimpsing the view from the Seine side of the apartment, Moore told Madame de Margeire, "Look at the bridge and look at the trees in front of the bridge. The best way to learn how to look is to draw."

"I don't really have the time," she says she told her visitor. "But with such encouragement, I have excuse to find the time."

And the perfect place in which to do it.