It was a little like the climax of a Broadway musical at the Mazza Gallerie shopping mall Saturday night. Milton Smith and Stimulus played--and sang--"Isn't She Lovely" as mayoral candidate Patricia Roberts Harris dramatically descended three flights of spotlighted escalators for her birthday party fund-raiser.

Past the sulking and sultry mannequins of Neiman-Marcus and Ann Taylor, Harris, who turned 58 on Thursday, waved every step of the way, and eventually all 500 supporters joined in with Smith's throbbing sounds, singing "Isn't she lovely, isn't she marvelous . . . "

After cutting one of her many green and white birthday cakes, the candidate made her way around the vast mall and back up the three flights--shaking hands, kissing cheeks and showering thank-yous all around. Her husband, Bill, an administrative law judge for the Federal Maritime Commission, made his way through the crowd by her side.

"You don't know how that made my month and helped the campaign," Harris enthusiastically told Janice Goldsten, a generous, new supporter. Goldsten and her husband, Robert--neither of whom had met Harris before--first learned she was running while they were vacationing in Florida. They sent a check for $2,500 immediately.

"After I heard her speak during her Senate confirmation hearings for HUD [in the Carter administration] I said I'd support that woman for anything," said Robert Goldsten.

While more than $25,000 was expected to be raised from the evening, the Goldstens were not your average contributors. Sponsored by a group of Washingtonians that included developer Oliver T. Carr and well-known Democratic activist Charles T. Duncan, tickets for the event ran from $25 to $250.

For $25, you had your run of the mall, mountains of little ham sandwiches and other snacks, and three hours of dancing to Smith's self-described "rhythm and blues" band. The $100 to $250 ticket-holders started their evening an hour earlier at Maxime's, a romantically lit, clubby French restaurant in the mall. A trendy snack of spinach quiche, crunchy green beans, French bread and strawberry tart was served.

"Everybody is trying to say I'm an elitist because they can't think of anything else to say," Harris responded to a reporter's question about her political image. "There are those who say blacks with an education are elitist, and blacks who work hard for their fellow person are elitist--well, I call it concerned. If as secretary of HUD I was elitist for trying to get housing for the poor . . . then I say let us have more elitists."

Harris' press aide, Jacqueline King, said the Harris campaign staff was concerned about talk that Harris is a "bourgie" (bourgeoise), an image she said they are trying to diffuse. King called the recent Associated Press--WRC-TV poll, which has Harris leading incumbent Marion Barry in the polls, "a reason to get out of bed in the morning."

But Harris seems to think that, for the time being, there may still be some advantage to being No. 2. "There are polls and polls and polls but I am still the underdog . . . I have a very tough fight ahead and I need a lot of support," she said. "I'm running against an individual Barry who has more money than he needs."

"The best thing that can be said for Pat Harris," said developer Oliver T. Carr, "is that she could stand up for this city without being an embarrassment."