When the Socialist government was elected here, jokes were made about jeans being worn to the Elyse'e Palace and serious concern expressed about the prestige of French fashion.

But both worries were laid to rest last night at a gathering of 450 designers, manufacturers, buyers and press in the grand salle de fe te in the Elyse'e Palace, France's White House.

The President of the Republic and Madame Mitterrand invited the fashion crowd over tonight to salute French designers and to boost the industry that is France's sixth largest export commodity.

"Everyone is inspired by you," President Franc,ois Mitterrand said. "You give color to the seasons, and tall bearing to us. Countries without mode and without designers are very gray -- they are countries in uniform."

In spite of the fact that it is only days before the French designers present their spring collections, few could resist the rare chance to visit the 18th-century palace. Many came with their favorite models and friends. Yves Saint Laurent escorted Catherine Deneuve, who said she had never been to the Elyse'e before.

"I came not as a designer but as a friend of Yves," said the actress, who in fact designs jewelry. She filled in words for her friend as he spoke a bit haltingly in English.

"It is a great event, because until this day the government made no effort for fashion, and France is the capital of fashion," said Saint Laurent.

President Mitterrand took advantage of the opportunity to be photographed with the couple, and with Marc Bohan, artistic director of Christian Dior. Bohan arrived with Princess Stephanie of Monaco, who assists him in the design studio.

"Is it not funny that all the presidents before don't accept fashion?" said Pierre Cardin. "They say couture is not necessary in life, and for the first time the Socialist government says, 'We applaud your talent and we need you to continue to make beautiful things for dreams and for industry.' "

"I suppose it is easier for some reason for this Socialist president to say it is okay to have luxury things. Surely he understands that it is good for export business."

Guests were asked to show identification along with their invitations as they stepped inside the gates of the Elyse'e on the Faubourg St. Honore', the street of luxury boutiques. Once they were inside, a chart, like a seating plan, indicated where they should stand for the president's speech -- designers and actresses to the right, manufacturers and artists at the far end of the room and the press behind a red rope to the left.

After the president spoke to the gathering -- digressing only once from his printed speech -- he passed the pages to a military aide and began making the rounds of the room with his wife Danielle, who was wearing a pale blue Mme. Gre s suit.

For the most part he simply shook everyone's hands -- introduced by Pierre Berge, Saint Laurent's business partner and the head of the Chambre Syndicale, an organization of the top designers here -- stopping to chat with just a few. Designer Jean-Paul Gaultier said the president was astonished when he saw Gaultier's associate, Francis Menuge, wearing a Gaultier skirt for men.

"We told him it was an expression of equality of the sexes, and that seemed to be all right with him," said the designer.

The president continued to shake hands around the entire room, including the press, and stayed on to chat and be photographed. The designers, who rarely see each other, chatted, drank champagne and nibbled pastries. One member of the English press sniffed about how the party given by Prime Minister Margaret Thatcher six months ago at 10 Downing St. "was a much nicer affair." "We each got properly announced and presented," said another.

Mitterrand understands that French fashion is a source of big business. "France is preoccupied with its financial and economic situation, and I think that the president of the Republic wants to help in any way he can," said Jacques Mouclier, the executive vice president of the organization putting on the fashion events -- the couture showings, the menswear SEHM show, as well as the ready-to-wear shows -- that have attracted 550 buyers, 1,200 journalists and 321 photographers from more than 600 newspapers and magazines and 35 countries.

According to Mouclier, fashion and accessories accounted for 11 billion francs (more than $1 billion) in exports. "Fashion, which was not considered a main contributor to the French economy in past years -- in fact, it was considered a bit frivolous -- is now considered important for France," he said.

Invitations to the evening's festivities called for city dress, which to designer Angelo Tarlazzi meant a navy blazer, tie and blue jeans. For Franc,ois Girbaud, codesigner with his wife Marithe of a line of streetwear, it meant white sneakers.

By 3 o'clock yesterday afternoon, Karl Lagerfeld still had not received an invitation to the party. "Maybe they sent it to Chanel, but I am not Chanel," said Lagerfeld, the artistic director of Chanel as well as the designer of his own collection in Paris and for Fendi in Italy. "With two collections going on, one has really no time for this bull----, and they should understand this because this is a working-class government."

As he started to leave the Elyse'e, Jean-Charles de Castelbajac seemed a bit puzzled. "It was like a surrealist situation, a dream for us all to be here together -- designers, journalists, store people. They even invited the artists who paint my fabric," said the designer. "It was an evening of eclecticism. Even those who didn't like each other were shaking hands."