MELBOURNE -- A new production of "Porgy and Bess," shaped in Washington and flown to Australia two weeks ago, looks like a smash hit even before its opening here Thursday night.

More than 20,000 of the 30,000 tickets available for its 15 performances in Melbourne had been sold before the end of August, with only minimal advertising.

"First time down under" is a tag guaranteed to set off box office telephones in Australia, whether it refers to London's Royal Philharmonic Orchestra or the rebel yells of Billy Idol. But even with this ad leverage, sales for Australia's first authentic "Porgy and Bess" have been exceptional.

More than just a "first time," it is "a once-in-a-lifetime opportunity for Australians," according to Robert Ginn, general manager of the Spoleto Festival, which is sponsoring the show. "It will be 30 years before they see 'Porgy' in this country again."

Janet Rushford has never seen an opera of any kind. But she didn't hesitate to buy four tickets to "Porgy" when she saw it mentioned in a color supplement in The Melbourne Age.

"For one thing, it's the only time it has been presented here in this form," she said. "And it appealed to me; I recognize some of the tunes like 'Summertime' and 'I Got Plenty o' Nuttin'. I relate to them more than to a heavier-type opera. I'm quite interested to see the black cast ... It's going to be very exciting."

Rushford, who describes herself and her furniture-salesman husband as "a middle-class suburban family," is just the kind of audience the festival producers hoped to attract. That's why they chose "Porgy and Bess" for Melbourne's second Spoleto.

"We saw the second year as the logical time to start two things," explained Ginn. "The first was to present material which was a little more accessible, allowing musical comedy audiences to cross over ... 'Porgy' is very appealing to both opera audiences and those not comfortable with 'Turandot' or 'Aida.' "

The festival's second aim was to produce original stage works, and not simply import existing productions. Gian Carlo Menotti, Spoleto's founder and artistic director, was enthusiastic when Melbourne suggested a new production of "Porgy and Bess" to achieve both goals.

But then a third challenge developed. "Porgy and Bess" might be the world's most accessible opera for audiences, but it is not very accessible for Australian singers. It requires an operatically trained cast of 45 black men and women, not only because of the story line but to comply with the will of the Gershwin Family Trust. The trust, which controls production rights, requires that only black artists be used when the opera is sung in English. From Nellie Melba to Joan Sutherland, Australia has been a fine training ground for operatic voices. But not for black singers.

So an American cast was assembled through auditions in New York and Washington. Two sets of principals will perform, to allow for rest between performances and to provide emergency backup. Director, conductor, set and costume designer and choreographer are American.

Apart from providing the funds, how else could Australia be a partner in the production? The costumes and sets were made in Australia, Melbourne children and goats were recruited for small roles and the State Orchestra of Victoria, which normally accompanies the Australian Opera, will provide the accompaniment.

So, the transpacific production of "Porgy and Bess" was launched, using electronic forms of communication. "The fax machine is more responsible for the success or failure of this production than any single person," declared Mark Schroeder, the festival's marketing and promotion manager. Because Australia is 14 hours ahead of Washington, someone manned the machine round the clock in the festival's offices on the sixth floor of a seedy old YMCA hostel next to the modern concrete-and-steel-towered Victorian Arts Centre where "Porgy" will open.

"We stay here all night. It's great for insomnia, terrible for sleep," Schroeder added. But, if production designers and coordinators in America wanted "a particular doorknob or table and chair," a sketch sent by fax was the quickest way to get the prop men on the hunt.

For the basic set, the Australians were able to work from three miniatures, accompanied by color photographs enlarged to provide details. Also guiding the construction team was a complete set of architectural plans, "just like a house," said Ginn.

"I wish we were building a house," he added. "It would be a lot cheaper."

To get the costumes right, the cast was measured in America for everything from head to knee sizes, and the five Australian costume companies worked from detailed sketches accompanied by swatches of material.

When necessary, people, as well as fax messages crossed the Pacific. A five-person Australian stage crew joined the rehearsals at the Kennedy Center, and an American design specialist flew to Melbourne twice.

"No, we haven't suffered a lot from the distance," Ginn said. "It's not so different from having rehearsals on the other side of town.