Last night, under the Austrian crystal chandeliers at the Kennedy Center's Opera House, the opera star groupies--2,300 strong--were out in full regalia. The object of their oohs, ahhs and bravos was Placido Domingo, who despite his name--which means "Peaceful Sunday"--aroused loud enthusiasm.

After the concert a crowd of top-level groupies, including Vice President George Bush and his wife Barbara, Kennedy Center chairman Roger Stevens and his wife Christine, and Sen. Edward M. Kennedy (D-Mass.) and his sister, Jean Kennedy Smith, went backstage and hugged and cheered him. Domingo was still excited by the thunderous standing ovation that extracted two encores from him. "It was fine," he said. "It went well. For six days I was in bed with a high fever. But now I feel able to go on to my next performance at the Metropolitan."

Obviously, the audience thought he was in fine form. He was overwhelmed with bouquets of flowers at the end of the program. Conductor Julius Rudel took his own bouquet and threw it to the Choral Society.

One enthusiastic concertgoer asked Domingo to have her picture made with him, and Kennedy yelled across, "She said she came to have a picture made with me. Now she's driving down your driveway." Domingo laughed.

Barbara Bush said, "It was just beautiful. I loved it. It's a nice change for my husband after worrying about peace." The Bushes drove in the stage loading dock of the Kennedy Center and went out the same way. But Domingo, Rudel and Domingo's wife, Marta, made a grand entrance into the dinner, which was held in the Musical Theater Lab.

Rudel, who was the first music director of the Kennedy Center, was the center of his own claque last night.

Joining Domingo for some numbers was Rachel Gettler, a mezzo-soprano, and the Choral Arts Society of Washington. Gettler, almost dancing off the stage in a filmy purple dress, said, "He is a wonderful colleague. I was thrilled."

The benefit was to redecorate the Opera House, whose genteel shabbiness is in peril of become plain shabby. The cost of the redecoration is estimated at $1.8 million, of which some $1.4 million has already been raised.

The sell-out evening netted more than $200,000. Tom Kendrick, director of operations at the Kennedy Center, said Domingo did not perform for free, but Domingo's fee was "very reasonable. He bent his schedule to accommodate us. After all, he can go wherever he wants to."

Not everybody's mind was totally on the music. Kennedy said that he hoped to get a jobs bill through Congress that was "better than the president's." Asked whether he thought the slump in oil prices would rescue the president from the recession, he said "lower oil prices will be good for the economy and the consumer, but we Democrats have a lot of work yet to do."

Alma Gildenhorn, an antique shop owner, and A. James Clark, head of the George Hyman Construction Co., were cochairmen of the Domingo Committee. Cochairmen for corporation gifts were Stuart A. Bernstein, a real estate investor, and John J. Mason, a banker. Cochairmen for patrons were two interior designers: Emily Malino and Victor Shargai.

Adding glitter to the gala were: Mayor Marion Barry and his wife, Effi; Spanish Ambassador Nuno Aguirre de Carcer and his wife, Maria Isabel G. del Arenal; former chairman of the Arts Endowment Livingston Biddle and his wife, Catharina, a painter.

"Who are all these people?" asked Clement Conger, curator of the White House and the State Department and chief fund-raiser for their antique collections. "I don't recognize a lot them. I must get the Opera Society's list."