Ronald Reagan set the theme Saturday afternoon, at the beginning of a long day's celebration on behalf of Ford's Theatre, and he repeated it near the end. The message was that the performing arts must stop looking to the government for support, but he put in a positive form. "In this country," he said in the East Room of the White House, "we have maintained by voluntary contributions more musical groups, more orchestras, more ballet and opera companies, more nonprofit theater and more cultural institutions such as libraries, than all the other countries in the world put together."

He repeated the statement six hours later, on stage at Ford's, at the climax of an epic fund-raiser for that financially troubled instituion. The message was sweetened with a joke or two ("incidentally, it is not true that I used to play this theater before it was closed 100-odd years ago"), but nobody who was paying attention laughed very much. Performing artists like Natalia Makarova and Itzhak Perlman listened with an air of concerned fascination, and the top executives of such corporations as Procter & Gamble, Occidental Petroleum and Sears, Roebuck heard a mandate to pick up responsibilities that the federal government no longer accepts.

"Do you think you will be giving more to the performing arts now that the government is backing out?" someone asked Armand Hammer at the White House. "I guess I'll have to," said the millionaire art connoisseur.

The entertainment, which was the centerpiece of the day's three-part activites, sometimes seemed a bit routine and colorless compared to the real-life dramas of money and power that were happening in the audience -- but it included a number of striking performances by artists who ranged from Twyla Tharp and Makarova to Juliet Prowse; from Lena Horne and Tony Bennett to Luciano Pavarotti; from Itzhak Perlman to George Benson, with notable comic routines by Dom DeLuise and Rodney Dangerfield.

As impressive as the list of performers was the guest list, which included not only the country's top political movers and shakers, but top executive officers of nearly 100 major American corporations, ranging alphabetically from Alcoa to Xerox. "The real purpose of this event is to introduce Ford's to corporate sponsors," said the theater's executive producer, Frankie Hewitt, who estimated that Ford's will clear about $500,000 from the evening's activities, including corporate activities, including corporate gifts and NBC's payment for the right to telecast the gala. "What's important isn't how much money we raise tonight, but who's sitting in those seats."

Ong after midnight, as "A Festival at Ford's drew to its glittering finale with a dinner-dance at the Organization of American States, Brad Butler, chairman of the board of Procter & Gamble, was saying the same thing more elaborately. P & G board meetings, he said, have been discussing "the need for corporations to step in quickly and support things that the government is dropping. We must be willing to support the things we think are important."

The Ford's benefit gala, which began at 5 p.m. at the White House and continued until after 2 a.m. at the OAS, mingled a lot of frivolity with the serious business of raising money for the performing arts.

"Holy Moses," said comedian Dom DeLuise strolling into the White House. "It's like a bar mitzvah."

Actress Victoria Principal, who served as co-emcee with actor Jack Klugman for the evening's entertainment at Ford's, entered the White House arm-in-arm with singer Andy Gibb and someone asked, "Are you two an item?" "That's a good question," she answered."Are we?" But a few hours later, on the stage of Ford's, the thought of Gibb seemed to distract her so much she forgot how to count up to three. As emcee, she introduced the singer with "two of the very nicest words I know: Mr. Andy Gibb."

Loretta Lynn, who had been identified as a strong Carter supporter during the last administration, revealed that "I'm a Reagan fan, too -- always have been," as she entered the Reagan White House.

"You can love more than one man, can't you?" she said.

The classical artists in the gala seemed more preoccupied with the reduction of government aid to the arts. "I will beg the president not to make cuts," said Makarova on her way to private reception Reagan held for the artists, and she kept her word.

"Everybody's talking about the cuts," Itzhak Perlman reported later. "I was in the receiving line behind Makarova, and she was saying 'mr. President, please . . .' So all I had to say was, 'Mr. President, please listen to her.'"

Reagan does listen to some of the people who were at Ford's: people like Speaker of the House Thomas P. "Tip" O'neill (D-Mass.) and Senate Majority Leader Howard Baker (R-Tenn.), whose wives, Millie and Joy, were the chief organizers of the gala, along with Hewitt. "Millie and Joy have shown where the real talent is in their families," said Ford's board chairman C. William Verity Jr. Reagan seemed to agree. "They worked so well together," he said. "I'll have to talk to their husbands about that."

The always-intrusive presence of television cameras took on a surrealistic air in the mid-19th-century atmosphere of Ford's, and the evening had that special quality, detached from real time and space, that characterizes events that happed so that they can be televised.

There were long pauses between the acts. While the stage was changed for the next number, the bright lights and television cameras were turned off, a murmur of subdued conversation would rise from the audience, and Victoria Principal, standing on stage at the microphone, would go into a kind of suspended animation. Then the red lights on the cameras would brighten, and a television director's voice would give the audience its cue: "Ladies and gentlemen, applause, please." Then obediently, some of the most powerful men in America would begin to applaud an empty stage, so that it would look right. Thursday night on the nation's television screens.