World of culture under the magnolias. Charleston, S.C., plays an elegant host to star-studded Spoleto Festival

The curtain has risen on the eighth season of Spoleto, U.S.A., the American photocopy of the intercontinental cultural exchange that Italian composer Gian Carlo Menotti started in Italy 25 years ago. Seventeen days of classical music, theater, dance, opera, jazz, and visual arts are sizzling through June 10 amid this city's antebellum houses, churches, and gardens.

The Italian version began in the poor and sleepy town of Spoleto, Italy, because founder Menotti wanted to take artists ''where they were needed'' to become ''the bread and butter of a community, not just the after-dinner mint.'' The so-called ''Festival of Two Worlds'' quickly became world renowned for its depth, variety, and opportunity for young artists.

For similar reasons, Menotti - a Pulitzer Prize-winner and the most-produced living operatic composer (best known for ''Amahl and the Night Visitors'') - transported an American version here in 1977. He chose Charleston because of its deserving, off-the-beaten-track heritage and a setting as rich with history, art , and beauty as the performances that would occur in its theaters, auditoriums, courtyards, and parks.

The current festival is studded with enough world-class talent to keep it on the road to international status on par with its prototype. Highlights this year include Menotti's own opera, ''Juana La Loca,'' Franz Lehar's ''The Merry Widow, '' Pinchas Zukerman and his Saint Paul Chamber Orchestra, the Paul Taylor Dance Company, and an American premiere of Australian playwright David Williamson's ''The Perfectionist.'' Also of note are Strauss's opera ''Ariadne auf Naxos,'' the Emerson String Quartet, Baroque cellist Anner Bylsma, and ''Daniel and the Lions'' performed by the New York Ensemble for Early Music.

There were standing-room-only crowds for many of the first weekend's offerings, begun with much fanfare amid speeches, parades, and soaring balloons. But the only real hint of a festival-in-progress outside festival sites are the multicolored banners flapping from streetlights. One million in ticket sales have been announced, and the town will net about $42 million in extra business. But when performance exits disgorge their enormous audiences, they seem to disappear among the magnolias and cobblestones.

It is this peculiar flavor of the Charleston/Spoleto marriage that led an editorialist to comment: ''The combination of the daring child, always dynamic, and the old lady of quiet charm who rarely changes . . . has produced an ideal mating.''

Among the ongoing offerings:

* ''The Merry Widow'': The opening performance of the festival was everything it one could hope for it - upbeat and crowd-pleasing, with first-rate costumes, glittering music, luxurious sets, and excellent cast. Singers and orchestra overcame Gaillard Civic Auditorium's notoriety as a horror of acoustics to receive rousing ovations.

Mary Jane Johnson, winner of the first Luciano Pavarotti International Voice Competition, projected the Merry Widow with flair and dazzle - both as actress and singer. With the strongest and most eloquent voice of the evening, her singing of the familiar aria ''Vilia'' earned her the only sustained mid-act applause.

Peter Puzzo as Danilo, James Stith as Baron Mirko Zeta, and Katherine Terrell as his wife, Valencienne, were also convincing as actors and singers.Artistic director Menotti unabashedly called the Spoleto Festival Orchestra's rendition on a par with a recent production by the Vienna Philharmonic.

There were many in the audience who disdained having the opera performed in German - evident by only diffuse giggling at the strongest comedic lines of the libretto. When queried, Menotti - known for writing and performing accessible operas - told me he does not want to play down to audiences as if they're in the cultural outback. ''I would only play contemporary opera in the language of the audience, not old standbys like 'The Merry Widow' - 1905.'' He hopes to present more and more challenging works in coming years.

* Chamber music concerts: The atmosphere of a slower and more elegant time is perfect for chamber music, and Charleston's restored Dock Street Theatre is just the ticket. One of the jewels of the entire American theater scene, it is replete with delicate, wrought-iron balconies on the facade, heavy velvet curtains, gilded medallions, and box seats (total capacity, 264).

True to the early Spoleto, Italy, days, when artists and programs changed fast and furiously, host and founder Charles Wadsworth announces programs verbally amid quips and entertaining banter. ''What can I say about Giovanni Battista Sammartina,'' he says, introducing one number by the lesser-known 18 th-century composer, ''that hasn't already been said. He and his brothers had a moving company just before he wrote this piece.''

The hit of all concerts has to be cellist Anner Bylsma, playing a smaller, thinner-sounding Baroque cello that he must suspend between his legs because it has no supporting peg. With Katherine Ciesinski singing Menotti's ''Songs of Far Away,'' followed by the Emerson String Quartet sizzling through Bartok, the Chamber Music Concerts have wonderful contrast and character.

* Paul Taylor Dance Company: The company began by performing two of its longtime classics: ''Aureole'' (1962), a lyrical, barefoot, modern-dance interpretation of classical music; and ''Three Epitaphs'' (1956), slumping and shuffling about a bare stage in what becomes a primordial folk dance. Mud-colored leotards from head to toe were designed by Robert Rauschenberg and adorned with tiny mirrors.

After intermission were works choreographed in 1982 and '83. The set of ''Sunset'' was designed by Alex Katz. It was an atmospheric, dreamlike look at courtship, with archetypal male and female figures. In general, the men were not up to Paul Taylor's usual high standards, despite their showcase solos and duets. Kate Johnson stood out of the whole troupe with her uncommonly lithe grace.

The evening finished with ''Mercuric Tidings,'' a blander modern-dance interpretation of classical music which Taylor already did more definitively in''Aureole.''

* ''The Perfectionist'' was a showcase of some of Australia's best talent, both playwriting and acting. Author David Williamson's (''Gallipoli,'' ''Year of Living Dangerously'') play had a successful debut in Australia, and this is its American premiere. The material may seem cliched and dated to Americans for whom the concept of open marriage as touted in the '60s is at least a decade old. But audiences showed great acceptance of this fast-moving, intelligent production. Performances were superior indeed.