As last night's party at the Watergate rose to its climax, Katherine Ortega, treasurer of the United States, was seated at a corner table autographing currency. It began when she was introduced to Placido Domingo and signed a bill for him -- and suddenly people were lining up and the table was covered with bills. "Who has the cards for this poker game?" asked Martin Feinstein, general director of the Washington Opera.

"That woman's signature is on every bill in your pocket," a bystander told a friend. "It's on this one twice," the friend answered, looking at the fresh signature on a slightly rumpled dollar.

Money was one of the motifs at last night's party; music was the other. It was a $100-per-ticket benefit for the Washington Opera Guild, including a preview at the MacArthur of the new film "Bizet's Carmen," starring Domingo and soprano Julia Migenes-Johnson. Both stars flew down from New York for the party; Migenes-Johnson lives there when she is not singing in Europe, and Domingo is currently busy there rehearsing for the Metropolitan Opera's "La Bohe me" next week, which will feature him not as a tenor but as a conductor.

Feinstein announced triumphantly that the Washington Opera has signed Domingo up to sing and is negotiating with Migenes-Johnson. Then he refused to say what roles are being discussed.

"All I can say is that Domingo will be singing a very romantic role," said David Lloyd Kreeger, president of the Washington Opera. "Martin doesn't want to announce it yet."

Pressed for more details, Feinstein finally joked, "We're going to do 'Fiddler on the Roof' in Yiddish with English titles." Domingo's voice is versatile, but it's really not right for the role of Tevye.

Most of the 200-plus fans at the party seemed to be equipped with cameras and many lined up to have their pictures taken with the stars of the evening. Nostalgia was thick in the air. "I first saw you in Vienna in 1974," one fan told Migenes-Johnson. "I've read about you in the German papers," said another. "You're a very famous singer."

"The first time I saw you," a woman told Domingo, "you were being swallowed by a sea monster and I fell in love." "That was Rameau's 'Hippolyte et Aricie' for Sarah Caldwell in 1966," Domingo recalled instantly. "I don't have to be swallowed by sea monsters any more."

Among those who remembered their first encounter with Domingo was Gian Carlo Menotti, who is in Washington to direct the Washington opera's "La Bohe me," which will also open next week. Menotti and Domingo remain friends despite being identified with rival "Bohe mes" and despite early difficulties.

"The first time I met him," Menotti said, "at the Ope'ra in Paris, I told him, 'I am thrilled to meet you.' He told me, 'Mr. Menotti, you have met me before; I auditioned for you and you turned me down.' "

"He was right," Domingo said. "I had just been married and I was not thinking about singing. My voice was cracking all over the place."

One colleague at the party, Broadway singer Karen Akers, was transformed into a fan for the occasion. "I am totally smitten with the lady who sang Carmen," said the star of "9." "She does so many things on so many levels."

Migenes-Johnson had not performed that evening except on film, but seemed to find the evening strenuous anyway -- including the long standing ovation she received after the film and then the busy encounters with hundreds of enthusiastic fans.

"Tomorrow," she said, "I'll have to go to the orthodontist to get my jaw straightened out from so much smiling. Iron out the cheeks and straighten out the jaw."