French President Francois Mitterand may have outdone even the th ree Louis who built it, lived in it and paid for it, with his party tonight for summit leaders.

In the Chateau de Versailles, where Louis XIV set an example that the rest of Europe never got over trying to copy, it seemed almost like old times. In the cobblestone courtyard there were plumed-hatted Gardes Republicains in red and blue uniforms lined up to greet Mitterrand's visitors, who've lived like kings themselves here for the past three days during the seven-nation economic summit. About 75 of the elite French military corps sat on horseback with sabers drawn while at their backs in the distance another horseman, the equestrian statue of the Sun King by Bernini, looked the other way toward the Place d'Armes.

It was another of the lavish events that have stirred controversy among the French over the cost of the summit. Variously estimated at between $11 million and $13 million, the conference and all of its trappings have raised questions of propriety in Socialist France, with its troubled economy.

First to arrive last night was Mitterrand and his wife, Danielle, who wore a green and gold full-skirted gown designed by Yves Saint Laurent. As Mitterrand's limousine swept into the courtyard, another corps of gardes Republicains raised its bugles and started the drumrolls to launch into "Fanfare."

In quick succession came Canada's Pierre Trudeau, West Germany's Helmut Schmidt, Japan's Zenko Suzuki, Britain's Margaret Thatcher, Italy's Giovanni Spadolini, President Reagan and his wife, Nancy.

Mrs. Reagan wore a one-shouldered white chiffon gown with beaded top, designed by Galanos for her to wear to Buckingham Palace last year at the royal wedding. Her earrings appeared to be diamond in a crescent shape and there were several pearl hair pins tucked in a chignon which her hairdresser, Julius, who is traveling with her, created after she returned from Normandy earlier in the day.

Guests entered the Chateau and mounted the broad stairway past more Gardes Republicains to file into the Hall of Mirrors by way of "the Queen's Apartment." In that case, the queen was Marie Antoinette, and the visitors probably remembered from their school lessons some of her eating and playing habits as they passed through her elaborately decorated bedroom.

In the elegant reception room the French call the Galerie des Glaces the leaders found nearly 250 French and American guests waiting for them. The sight of that dining room table almost stretching the length of the 243-foot-long room--one of the world's longest--must have given pause to some of the guests of honor.

Overhead, flashing like thousands of diamonds, were crystal chandeliers reflecting light into the mirrors that gave the room its name. Adding to all this were countless pieces of marble, bronze, brass, gilt and other lavish artifacts set among priceless antique furnishings.

Guests could look through the open doorways to the spectacular gardens of Versailles, where fountains played in the approaching twilight. The table was set with such precision that guests at one end could see in a straight line through the crystal goblets to the other end. Not one appeared to be a single millimeter out of line. There were dozens of ornate silver candelabra, all with tapers flickering, and arrangements of yellow daisies, blue sweet peas and pink roses. The tablecloth was embroidered with golden stars and beside each plate were a menu with a picture of Georges Braque's "L'Homme a la Guitare" on the cover.

The Mitterrands sat in the middle of the table across from each other, a distance of about 2 1/2 meters. On Mitterrand's right was Mrs. Reagan and, on her right, Trudeau. To Mitterrand's left was Hannelore Schmidt. Across from them with Danielle Mitterrand was President Reagan, quite by accident in full face for American television cameras that were swept along in a pushing, shoving, noisy media pool representing the same seven nations as the leaders.

On Reagan's right was Margaret Thatcher, but it was Danielle Mitterrand he seemed to be anxious to communicate with, although he was unable to do so without calling forth an interpreter. Spotted elsewhere along the table were U.S. Ambassador Evan Galbraith, White House Chief of Staff James A. Baker III and Secretary of State Alexander M. Haig Jr. The French in the crowd far outnumbered other nationalities, however. There were members of the French National Assembly and Senate, trade union leaders, business and even a couple of movie stars, one of whom was identified as Daniel Gelin.

Guests dined on lobster with a sauterne sauce, stuffed lamb, heart of lettuce salad, assorted cheeses and dessert called "Velours de Versailles a la Liqueur de Grande Marnier." The wines were a 1979 Meursault Goutte d'Or, a 1970 Chateau Fombrauge and Laurent Perrier Cuvee Grand Siecle.

Security was as elaborate as the surroundings and behind Mitterrand and Reagan stood squads of bodyguards.

From the dinner, guests were taken to the Royal Opera for a performance that lasted roughly 45 minutes and which Treasury Secretary Donald Regan later quipped that he would have "called an operetta." After that there was a display of fireworks.

As spectacles go, Louis XIV might have been hard-put to come up with one as extravagant. And to follow this act, next year's summit host, the United States, might be equally hard-put.