Working class discturbed the velvety lunch-hour atmosphere at the Sans Souci restaurant near the White House yesterday when 15 waiters, cooks, pot washers and union organizers, some wearing Jimmy Carter masks, threw up a picket line at the door.

Under the crystal chandelier and gilt mirrors inside, the posh restaurant's 100 or so seats were nevertheless almost completely filled with loyal patrons, including lobbyists, lawyers, media brass, foreign and domestic government officials, who crossed the lines.

"I expect business will be off tomorrow, though," said one picketing waiter, as a welldressed woman smiled her way firmly through the line. "After all, today they already had reservations."

The restaurant employees said an owner of the Sans Souci had fired two waiters last weekend because of their participation in union organizing.

Though the two have since been rehired, the employees said they are picketing because of other instances of intimidation and threats of firing and blacklisting by the owners. They said they want the union in order to get health and retirement benefits, higher pay and better working conditions. They said the kitchen was "like an oven," and lacked proper ventilation.

Sans Souci owner Bernard Gorland was busy refilling water glasses and performing other chores in the absence of most of his employees.

He said he had indeed fired two waiters, because he felt they were "not good for the place," but had rehired them after his lawyer told him the firing was illegal in the wake of their union involvement.

He called on his customers in a written statement to "appreciate the fact that we are being coerced" and said he ownership would insist on a secret ballot election supervised by the National Labor Relations Board to determine whether the majority of employees want the union.

The restaurant has 33 employees. The picketers estimated that 17 of them favor joining the union.

Tony Machado and Charles Le-Morzellee, the two waiters Gorland had attempted to fire, said they make $49 a week, plus tips. "With tips, it's about $350 a week." Machado said.

Asked later if that was an accurate estimate of his waiters' earnings. Gorland responded: "If you believe in fairies." He suggested that tips added up to more than that.

Columnist Art Buchwald one of the restaurant's best-known regulars, came through the picket line head down, elbows up. "No pictures, no pictures." he said to press photographers there.

Once safe inside, he shrugged sheepishly and said. "Well, a guy's gotta eat somewhere." Buchwald has a standing reservation at the same table every day.

Dan O'Brien, a businessman who eats at the restaurant regularly said he crossed the lines because. "I got a guy in there waiting for me. Now I know the problem. I don't come tomorrow. All right?"

Hobart Taylor, a lawyer who served as an assistant to President Johnson, said. "I didn't see any line when I came in. I don't know what it's all about yet. I might have an opinion later. But I'm a regular there and I like the place."

Among others who lunched at Sans Souci yesterday were the Nigerian Ambassador Edward O. Sanu and several Nigerian government officials. Robert Hormats of President Carter's National Security Council. Mel Elfin, a senior editor of Newsweek magazine, and Phillip L. Geyelin, editorial page editor of The Washington Post (who was keeping an appointment with Buchwald).

Paul DeLisle, the maitre d'hotel of Sans Souci, who is noted for his unflappable efficiency and charm, said it had been a difficult lunch. "We appreciate that the customers were patient with us."

He declined comment on the labor dispute itself because, he said. "I must work with both sides."

Another source close to Gorland, watching the pickets sadly, said. "I don't know what the union stand is yet, but I think the other side of it is the feeling that after all those years of struggle, the place is making it now and these fellows want to come along at this late date and take advantage."

"It's a machismo thing," said Ronaid Richardson, an official of the Hotel and Restaurant Employees Local 25. "It's his Gorland's) place and the employees just aren't going to tell him what to do."