"Who says you can't come home again?" Beverly Sills asked with her familiar big smile. "I have the marvelous feeling of coming home again."

Sills, formerly the prima donna and now the general director of the New York City Opera, was back at Wolf Trap Farm Park, where she has long been a member of the board of directors. She sang a farewell performance of "The Barber of Seville" at Wolf Trap on a rainy July evening in 1980. "I remember the rain stopped long enough for me to sing 'Una voce poco fa' the opera's biggest show-stopper without background noise," she says. "Sometimes things go right."

Not always. Since that memorable evening, she, her opera company and Wolf Trap have all been through a lot of problems. But tomorrow, the City Opera finishes a week-long run at Wolf Trap with three productions that have been warmly welcomed by critics and audiences. It is the first time the City Opera has performed there since 1981.

In 1982 Wolf Trap's Filene Center burned down; this summer is its first full season since then in the rebuilt, fireproofed facility.

In 1983 the City Opera was crippled by an orchestra strike that closed down almost its entire season. An organization that had been in serious financial trouble when Sills became its manager was pushed to the brink of bankruptcy. While the Metropolitan Opera (lavishly headquartered next door to the City Opera in New York's Lincoln Center) prepared to celebrate its 100th anniversary, fans began to wonder whether the younger company would reach its 40th. Sills continued to radiate optimism, but the smile was a little less easy in her frequent television appearances and she began to put on weight.

Today, Beverly Sills is back at her fighting weight, looking as trim as when she used to hold audiences spellbound in bel canto opera. The optimism has returned, as easy and spontaneous as ever, and now it is supported by firm union contracts, a three-month season with no competition from the Met, and $10 million in endowment funds raised during the last few years. Like Wolf Trap, the company has plunged into disaster and come out the other end, still standing up and throwing punches.

"I'm not raising life-or-death money any more," Sills says. "I could not have made that statement when I walked into this job five years ago."

She has not really come home to the Filene Center where she gave her farewell performance; that building is ashes. But she is haunted by familiar sights carefully reconstructed. "If you go downstairs backstage, it's exactly as it was before," she says. "The whole company settled in almost instantly. I walked without a thought right into my dressing room, which is now my office."

The company's status has even reached a point where it is being used for fund-raising by other organizations. "Wednesday night," she said, "we had a benefit performance for the Alexander Graham Bell Association, which helps deaf children and offers all kinds of educational information for parents. For obvious reasons two of her five children are deaf , we are very close to them. We had a little dinner for about 400 people, and we raised about $150,000 for them, which tickles us a lot."

In bygone seasons, the City Opera came to Wolf Trap after its winter season. This year, and for the foreseeable future, it will be having no winter season; the run at Wolf Trap precedes its summer season, which will open on July 5 with "The Student Prince." "It attracts a young audience," Sills said, "and maybe while they're at it they will hear about 'Lucia.' It couldn't hurt."

The season will include the three operas presented here, "Turandot," "Madama Butterfly" and "The Mikado," but its highlight will be a Lincoln Center festival of the bel canto operas (early 19th-century works that feature spectacular singing) in which Sills made her own international reputation.

Variety and innovation have always been a key motif in the City Opera's productions, and this year's fall season will continue that tradition. Among the offbeat productions being presented are Prokofiev's "Love for Three Oranges" (with sets and costumes designed by Maurice Sendak), "Akhnaten," by Philip Glass, and a new production of "Kismet" -- starring George Hearn, who will take a leave of absence from his Tony-winning performance in "La Cage aux Folles."

Hearn will also sing the title role in the New York premiere of Dominick Argento's "Casanova!" Nov. 1. This opera had its world premiere in Minnesota last April under the less New Yorkish name of "Casanova's Homecoming," and the City Opera will make it the occasion for still another (sometimes badly needed) innovation: the projection of English surtitles for an opera that is being sung in English. These are only highlights of a season that paints a picture of a lively, imaginative and flourishing opera company.

In fact, the City Opera finished its last season with a small budget surplus. "We aren't trying to make a profit," Sills explains almost apologetically, "and the money we had left over will be spent almost immediately in July. But we are reducing our accumulated deficit and expect to get rid of it totally in a few years. Money for payment of past debts is hard to raise; nobody wants to pay for a dead horse.

"I was a little worried about the summer season last year, so I budgeted very conservatively and that gave us the first surplus we have ever had. I'm running a very tight ship. I'm interested in every invoice that comes in and goes out; I nickel-and-dime everybody and will continue to do so as the company gets healthier and healthier. I know how hard it is to raise money and how easy to spend it."

On the bel canto festival planned for this summer, she says it doesn't seem strange to be presenting younger singers in the roles that once made her famous. "I try to tell the young women that it's not necessary to do it the way I did it: 'This is not a revival of a Beverly Sills production, this is a revival of a Donizetti opera.'

"Sometimes, I'll be walking across the stage, through one of the sets that I sang in, and I'll look over my shoulder at the set and a wave of nostalgia will sweep over me for a minute. Then I think, 'Thank God I don't have to do that any more.' "