After Joan Kennedy stood in the reception line shaking hundreds of hands, fulfilling her duties as chairman of the Washington Opera Ball, she turned to Martin Feinstein, director of the Opera, and said, "I'd almost forgotten what it was like to be in politics."

And so it went last night at the ball at the Swedish Embassy, its annual fund-raiser where taffeta skirts rustled by, champagne corks popped, and perfume settled in the air like a blanket. There was also a sumptuous buffet of sausage, smoked salmon, pate and more at the ball -- which followed 24 dinners for guests at 24 different embassies. A night of nonstop food.

And a night of nonstop mingling for the more than 500 who attended. Among the food and the Republicans (Michael and Carolyn Deaver, and Elliot and Anne Richardson) and the Democrats (Rep. Claude Pepper of Florida and former secretary of the treasury G. William Miller) the biggest celebrity of the evening was Joan Kennedy. She arrived at the ball wearing a taffeta dress with red bodice and plaid skirt and promptly disappeared into the ladies' room. "She went to the ladies' room about half an hour ago," said Betsy Rea, one of the organizers of the ball. "You know, she's so shy."

Joan Kennedy came alone. "She's very vehement and adamant about that," said Rea. "She made it very clear to us that she was coming here alone, on her own, and she didn't want us to provide an escort."

When Kennedy emerged from the ladies' room and decended the steps, taking a circuitous route to the receiving line, she answered questions about being back in Washington with, "Oh, I come back all the time."

She would not answer questions about being on her own in Boston. (She and her estranged husband, Sen. Edward Kennedy, are filing for divorce.) "Well, you know why I'm here," she said quietly. "For the Opera and for the Kennedy Center."

Asked about what she plans to do, she said, "I've had a lot of offers." She said some of them were in television, "talking about the media and the arts . . . I think it would be wonderful to work with television. So many children watch. I want them to know there's classical music as well as rock." c

And she seemed as concerned about budget problems as everyone else in these days, talking about the problems of music teachers, something she's been familiar with from teaching in Boston. "A lot of our funds have been cut off," she said. "The first thing to go are our music teachers."

Meanwhile, in the receiving line -- where Feinstein and Kennedy were joined by Wilhelm Wachtmeister, the Swedish ambassador, and his wife, Ulla -- most came through with a simple "nice to see you," for Joan Kennedy. u

Debra Biddle, a secretary for Eastman Kodak, had a little different reaction. As she shook Kennedy's hand she looked slightly puzzled. Until she realized it was Joan Kennedy.The she smiled and said, "This is just like meeting Elizabeth Taylor."

Sean Donlon, ambassador from Ireland, stopped to tell Kennedy how well she had done at the Irish night at the Boston Pops. "She did 'Peter and the Wolf,'" said Donlon, "and she brought the house down. How could she not do well?"

Most guests walked into the Swedish Embassy happily talking of their various dinners. Most said they were great. "We had duck," said Elliot Richardson, who ate at the Embassy of South Africa. "It's so nice when people tell me they enjoyed their dinner," Rea sighed contentedly.

Mayor Marion Barry had dinner and "just a little chit-chat" at the Organization of American States. "I was looking for a little support -- in case I decide to run again next year," said Barry, who was there with his wife, Effi. "Friends have been urging me to run. I've been trying to resist for a little while. At some point, I'll give in."

Through the evening, Martin Feinstein beamed, standing in the receiving line, bouncing up and down a little as he greeted his guests. Those guests paid $185 a head for dinner and the ball, and the Washington Opera hopes to make $130,000 according to Feinstein.

"I think it should be $250 a head," said Feinstein. "When you sell out six weeks in advance, you have a product people want. People love it, it's very special."