Helgi Tomasson 20 and counting.

THERE COMES a moment in the regimes of all ballet directors, when, hopefully, they can stop, exhale, and mutter to themselves, "Mission accomplished." For Helgi Tomasson, "it was during last spring's Balanchine Festival. They were dancing so well. I knew at that moment that we had really made it."

That rush of satisfaction was a while in coming. Tomasson will celebrate his 20th anniversary as artistic director of the San Francisco Ballet at a January 26 gala at the War Memorial Opera House. One of the longest-running tenures among major American ballet companies, Tomasson's was launched in a firestorm of controversy, Former artistic director Lew Christensen, who had recommended the retiring New York City Ballet principal dancer for the post, had recently died, and the ballet's board had declined to renew the contract of Christensen's protege and heir apparent, Michael Smuin. Local balletomanes wondered, "Who is this Helgi Tomasson?" The dance community sizzled. Partisanship reigned. Picket lines gathered. Dancers' loyalties were cruelly tested. One remembers bow Tomasson's cool, guarded manner, sense of purpose, innate belief in the ideals of classicism, and just plain decency defused a situation that might have been fatal to the country's oldest professional ballet troupe. Viking roots do tell, after all.

Twenty years later, a mandate has evolved into one of the generation's more heartening success stories. Tomasson can now sit in his airy Ballet Association Building office and recall that turbulent period in tranquility. Back in 1985, change was blowing through the dance world. SFB's president Richard LeBlond had advanced a theory that the complexion of American ballet was changing. The ancient distinction between national and regional companies was dissolving. Under Tomasson and with full board support, SFB was deemed the organization that could shatter those arbitary classifications.

Long ago, the company's vaunted repertory dispelled fears that the troupe would become a "Balanchine clone." Tomasson will tell you that his dancing years at the Harkness Ballet and The Joffrey shaped his tastes in choreography almost as much as his 15 years at NYC Ballet. Partially because of what it programs--everything from Bournonville to Morris, with stops at Ashton and Petit--SFB has become a destination for dancers from all over the planet.

It's a mixed blessing, but Tomasson accepts the process of globalization. "The old, national company styles of dancing have broken down. You won't find the pure Bolshoi or Danish or Royal Ballet look any longer," he says. "Only the Paris Opera Ballet has been able to preserve that integrity. When I had just come to Copenhagen from Iceland, I wasn't permitted to dance at the ballet, because I wasn't Danish. Now, that company is at least 30 percent non-Danish. The process really began at NYC Ballet, when, in my time, we had dancers from France, Germany, Denmark, and Canada."

Internationalism--the contingents from France and the Hispanic countries stand out these days--has lent SFB a fascinating range of phrasing and sensibilities. Tomasson takes pride, too, in the homegrown talents, developed from the SFB School, which he reorganized from the ground up. "It was wonderful for me to watch Joanna Berman and Elizabeth Loscavio rise to become major stars," he says.

Among the moments he cherishes: "Certainly, staging Swan Lake (1988) was important for me, as a choreographer. Every classical company worthy of its name should have one of its own." For some observers, 1987, with its classically stretched commissions from James Kudelka and William Forsythe, was the watershed year. "And Billy still owes me another new piece," Tomasson observes.

His relationship with Jerome Robbins, which was strong at NYCB, remained steadfast when Tomasson moved west. "Jerry loved to fuss over everything, but when he allowed us to do one of his ballets, he didn't even bother to come out here to check it out. He trusted me to do it right. I was very proud of that."

This season, Tomasson will honor his collaboration with the late choreographer when he revives Dybbuk. It premiered, to an original Leonard Bernstein score, in 1974 with Tomasson and Patricia McBride, and then vanished from the repertoire.

"Jerry was so sensitive to criticism," Tomasson recalls. "When there were complaints that the ballet was not true to all the details of the play, he withdrew it and replaced it with what he called Dybbuk Variations. But the original version, which we will do, is so much stronger. I think it's one of Jerry's greatest works, maybe because it reflects on his Jewish background."

Tomasson prowls constantly for new choreographers working in the ballet idiom, and he is often dismayed. "So many people want to make an impression right away. You will see a wonderful lift, and then it is repeated and repeated. They need to shape the piece and not be so concerned with achieving an instant success. Wowing an audience does not necessarily make an artist." That statement might serve as the motto for Tomasson's own career--onstage and off.