When the President of France and Madame Giscard d'Estaing throw a party in honor of President and Mrs. Carter at Versailles tonight, the event will take place in the former royal residence of Louis XIV and the current residence (in the tip of one wing, but still . . .) of Versailles curator Gerald Van der Kemp and his Washington-born wife, Florence.

Grand occasions such as state visits, and evnts as diverse as the Black African summit, and a fund-raising salute to American and French fashion, have made the palace and museum of Versailles come alive many times before. But in between, in a royal apartment once used by a minister of Louis XIV, the Van der Kemps regularly entertain in a style sufficient to rank them among France's outstanding hosts.

This is so, if for no other reason, because of the grandeur of the setting, with its extravagant buildings and grounds, Marie Antoinette's farm, the Hall of Mirrors and gilt and glass everywhere.

Once a Washington society columnist, Florence Van der Kemp moved into Versailles, bag, baggage and some fine French furniture when, 17 years ago, she married Gerald Van der Kemp, Versailles' curator for 29 years. ("His theory is that you must be hitting the small nail on the head all your life if you want to accomplish anything," she says.)

If the apartment is her home, she has no trouble remembering to whom it really belongs when the tourist arrive. The Duke of Windsor consoled her once by saying, she recalls, "In the morning when the sun is coming up and you open the window and look out in the courtyard you say to yourself, 'It's all mine.' However, at nine o'clock all the tourists come . . ." Van der Kemp trails off laughing. "It's entirely different."

She was brought up in Washington in a house on Massachusetts Avenue near Sheridan Circle. Her father, an Bureau of Yards and Docks, head of the shipping board and a successful inventor.

She did all the super-proper things attended the right schools - Holton Arms and schools in Rome, England and Paris; the training ground for her first job writing a column, "By the Way," for the Washington Star in the late 1930s. Betty Beale succeeded me," she says.

There were two husbands before Gerald der Kemp. Donald Downs and then another with whom she lived for 12 years in Mexico and about whom she will only say, "He wore jeans divinely."

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She had returned to Washington for her daughter Roberta's debut at the Sulgrave Club, found herself in the same circle of friends she had known 20 years earlier and remembers scolding herself, "Florence, you have got to get going. You can always come home."

She decided on Paris, since she was acquainted with the language from a French governess and school classes. "I'll tell you honestly. I was brought up that the world belonged to people who could make decisions and the ones that couldn't were never heard from again," she says.She recalls hesitating, as a child, in the choice of chocolates from a box and her father saying, "Give nothing to this child if she can't make up her mind."

In Paris, some Washington connections helped her get a proper house where she transferred her furniture and six Mexican servants (her now there are four) and met many Frenchmen including Gerald der Kemp. ("I had met Gerald before, but I had forgotten him," she says.)

Once in Versailles - with her mother's reception-room furniture established in the downstairs yellow room of the six-bedroom, 2 1/2 bath apartment, the china and silver from what she had in Washington, and dining-room chairs from the chateau (with eight additional matched ones which they bought themselves) - the Van der Kemps started to entertain grandly. (Some of her frequent guests, including Washingtonians Deeda Blair and Mary Lasker, will be guests tonight at the reception for President Carter.)

"My husband already knew the Dillons and the Bruces, and I knew a lot of people since I lived all over the world, so I could be a little help to him in public relations and receiving people," she says.

Much of the Van der Kemp's entertaining is groundwork for hard-driving fund-raising for Versailles, a zealousness interpreted by some in France as an excuse to entertain their friends in a royal setting.

"We like people giving money to Versailles," commented one Frenchman, "but we would like them not to mention it so much."

After teasing about her style of entertaining as being "like 'come into my parlor said the spider to the fly,'" she starts off with some ground rules.

"The most serious mistake any hostess can make is to be original with her food. Stick to simple things that are familiar. Otherwise the cook is a nervous wreck."

She has 25 menus, many of them holdovers from her mother. She switches them around, but never disgresses except to change the vegetables.

"If you are a professional hostess, it is stupid to be original and it's ridiculous to try and order food for color. I consider that the best quality food, simply served and well prepared, and served on a gold plate is what makes a party."

Occasionally she uses a gravy boat from her collection of pipisoirs, or antique chamber pots, estensibly used Centuries before in the royal chapel. According to Mrs. Van der Kemp, one couldn't leave the chapel until the minister finished the serivce and maids would stand behind their madames to attend those in need.

Dinner is set on small table rounds - "I don't believe in one table, it ruins the conversation," she says, and besides, she can't get laundresses who can do large table clothes properly. The dining room is decorated in cotton copied in Lyons, at the curator's suggestion, from royal silks and satins of Napoleon's day.

At each table she puts a judge or minister's wife "so everyone feels important" and at the smaller tables she seats the most beautiful women "so no one feels left out."

For her clothes, the formula is equally simple. All dresses come from Dior via a friend of her husband. "But I travel in Chanel suits because you can sleep in a Chanel suit, get up, powder your nose, and be ready for photographers."

Most of the housewares, even the beds and the pots, come from Bloomingdale's. "Would you tell (store president) Marvin Traub," says Van der Kemp, ever the fund-raiser, "that I would like to sell him the slogan I always use - You could live without Bloomingdale's - and then give the money to Versailles."

By 9 o'clock most mornings she is in her office working on correspondence about Versailles and occasionally returns there after dinner. She is not paid. "What I do is for my husbond's dreams so they can come true."

Nor does she worry that sometimes her French is not perfect. "The most important thing is getting things done," she says. "And if they are not so perfect, people are often more friendly toward you."