It's safe to say that Mark Morris's beguiling staging of Sylvia is not your grandmother's Sylvia‹even if your venerable ancestor had been hanging around London in 1952, when Frederick Ashton introduced his first version of the 19th-century ballet.

Who is this particular Sylvia? What is she, that all our dance aficionados commend her? The San Francisco Ballet will introduce Morris's version to New York this month, as part of its weeklong engagement at Lincoln Center Festival, July 25-30. It is the first original staging of Sylvia by a U.S. company, and it couldn't have happened to a more neglected or more deserving ballet heroine.

Few works of the classical dance repertoire are as well chronicled in the history books or as infrequently revived as Sylvia. This mythological romance about nymphs, shepherds, lusty huntsmen, and assorted deities was introduced at the Paris Opéra in 1876 through Louis Mérante's choreography, all of it now lost. What has survived is Léo Delibes's gloriously hummable and subtly orchestrated score (lauded extravagantly by Tchaikovsky, who, of all ballet composers, knew quality when he heard it).

As one might have guessed, it was this score that seduced the profoundly musical Morris when, six years ago, the San Francisco Ballet's artistic director, Helgi Tomasson, offered the choreographer a commission to create a full-length work of his own choice. That Morris is a modernist working in a ballet tradition has astonished no one in San Francisco. The commission epitomizes the innovative approach to the classical repertoire that has been adopted by Tomasson during the past 21 years.

Morris was working without a contemporary performance tradition when he prepared his Sylvia in 2003-04. He did, however, peruse an old Ashton Royal Ballet rehearsal tape. And he studied the original Sylvia libretto by Jules Barbier and the Baron de Reinach, which, Morris notes, includes extremely detailed stage directions. He also found much to ponder in the ballet's source, the pastoral play, Aminta, by the 16th-century Italian poet, Torquato Tasso. From there, Morris was on his own and he knew where the pitfalls lay.

"The problem with Sylvia," says the choreographer, "is the plot. It's the kind of complicated story you'd expect to find in a grand opera, not in a ballet. It's about all these people falling in love with each other and not being loved in return. And everything is there in the music."

Do not expect Sylvia to receive The Hard Nut treatment. Morris has not infused his version of the ballet with contemporary trappings and values as he did with his staging of The Nutcracker for the Mark Morris Dance Group. Indeed, he seems as much enamored with the spirit of late 19th-century French cultural fads as with the score.

"I didn't want to update Sylvia," Morris says. "That's not interesting. The ballet doesn't mean anything else than itself. I was fascinated that the premiere production may have featured the first use of electricity in French theater history, and did you know that there was a real, flowing stream on stage?"

Morris was also intrigued by 19th-century Europe's passion for what was once called "Orientalism." That explains the lavish production number he makes of the arrival of the pirate ship (with the disguised Sylvia among the harem slaves) in the final act. "It's part of the vogue for that exotic other world of the East. It's licentiousness unleashed on this Apollonian town. And," Morris notes, "the scene involves one of the first times that anybody heard that recently invented instrument, the saxophone."

In this episode, Morris accomplished something daring. He persuaded the women dancing the slaves‹who double as the nymphs of Diana‹to shed their pointe shoes and perform the scene barefoot. "And you will please notice that all their toenails are painted tangerine," he adds.

That the dancers of the San Francisco Ballet are willing to risk splinters or worse for Morris may explain the salubrious effect he has had upon the company since he bowed with Maelstrom in 1994, a relationship that will continue with a premiere for the 75th-anniversary season in 2008. No other dance organization, aside from his own, claims so much of his attention.

"The San Francisco Ballet is the best ballet company I know," Morris declares. "I went back there at the end of the season, when they should all be in body casts, and they were strong and eager and friendly and didn't look like they were dying of malnutrition. I walked in to rehearsal, said, 'Let's go,' and they did."

Morris praises the manner in which the company keeps his dances from disintegrating in his absence. But he reserves his highest compliments for the boss: "Helgi is a good choreographer and he's not scared of other choreographers."

The works on the Lincoln Center Festival mixed bill, all of them New York premieres, confirm that statement. They represent a diversity of repertoire that other companies justifiably envy. Tomasson will tell you that, although his 15 years as principal dancer at New York City Ballet were the apex of his performing career, his interest in choreography was significantly shaped earlier by the incredibly varied fare he had danced at the Joffrey Ballet and the Harkness Ballet.

Commissioned for the company's launching of a Paris dance festival last summer, Christopher Wheeldon's Quaternary finds the brilliant young neo-classicist working with a quartet of composers of violently contrasting sensibilities (Bach, John Cage, Arvo Pärt, Steven Mackey) in a "four seasons" structure that encompasses movement ranging from torpid to frenetic. William Forsythe made his San Francisco Ballet debut with the premiere of New Sleep in 1987, and if any commission distinguished Tomasson's regime from his predecessors', this foray into European dance drama was it. The Lincoln Center Festival visit includes Forsythe's Artifact Suite, a condensed version of the full-evening Artifact, made for Ballett Frankfurt in 1984. Virtuoso corps contributions, a pair of high voltage duets, and some wry comments about the nature of perception (signaled by a curtain which marks transitions with the finality of a film editor's razor) will arouse cheers and controversy in equal measure.

Tomasson's 7 for Eight, a highly spiced neoclassical outing to assorted Bach movements, has proved to be one of the choreographer's more personal pieces of recent years. It is primarily a tribute to a company of international artists who have been nurtured on the West Coast.

One of them, the Ukrainian Yuri Possokhov, retired officially at the end of the home season. A former principal at both the Bolshoi Ballet and Royal Danish Ballet, Possokhov joined the San Francisco Ballet in 1994 and represents the very best of Tomasson's achievement. Possokhov has agreed to dance through the Lincoln Center engagement, so these truly will be his farewell performances, and for those of us who watched him send shock waves through the company for a dozen years, the genuine end of an era.

Bay Area-based Allan Ulrich is an online critic for voiceofdance.com, a senior advising editor at Dance Magazine, and a contributor to a number of publications here and abroad.