How many conductors can say their first set of tails were Grandma's hand-me-downs?

Michael Tilson Thomas, music director of the San Francisco Symphony, is probably one of the few.

Then again, when it comes to his paternal grandparents, Tilson Thomas has a repertoire of out-of-the-ordinary tales.

They were the legendary Boris and Bessie Thomashefsky, founders and stars of New York's Yiddish theater. Strong-willed immigrants from the Old Country, they became megastars of the early 20th-century Lower East Side — "kind of like the Elizabeth Taylor-Richard Burton of the Yiddish theater," Tilson Thomas said.

Today their influence lives on in Tilson Thomas' treasure trove of theatrical memorabilia and in das pintele yid, that little spark of Jewishness that informs his musical interpretations.

Eager to share his grandparents' heretofore untold story, the conductor will have a major hand in compiling the "Thomashefsky Project," an exhibit and performing arts program founded and curated by Linda Steinberg, former executive director of the Jewish Museum San Francisco.

The nascent project, which is expected to be completed in 2001, will recall through artifacts and artistic recreations the impact of the Thomashefskys on America's theatrical, musical and film traditions.

It will travel throughout the United States, going on to Europe and Israel as well, Steinberg said.

Its compilation will involve scholars, translators and archivists from such institutions as U.C. Berkeley, Harvard, Stanford and Brandeis universities.

Tilson Thomas will serve as the principal narrative voice for the project, and will contribute everything from original costumes, scripts, posters, scores and playbills to mirrors, jewelry, crepe hair and an elegant lorgnette that once graced his grandma's dressing table. He keeps the valued family objects in an undisclosed location, and is anxious to finally bring them to the public eye.

"The fact that these two immigrant kids could just say `Let's do this' and then make it happen…I think it's an extraordinary story," he said, sitting on a couch in his Davis Symphony Hall study during a break from rehearsing Gustav Mahler's Symphony No. 9. The San Francisco Symphony is currently performing a 10-concert series featuring the Austrian composer's works.

The conductor, who is in his third season as music director of the symphony here, never met his grandfather, who died in 1939, five years before Tilson Thomas was born. His grandmother, on the other hand, played a significant role in Tilson Thomas' life.

Growing up in Los Angeles, he remembers sharing story-rich Shabbats with her. He recalls the legions of fans who showered her with gifts and autograph requests. And he can picture the circle of Jewish women who gathered around her weekly for lively recitations of monologues, scenes and songs.

"She was certainly different than other people's grandmothers," said the conductor, whose passion for the Thomashefskys is as contagious as his storied exuberance for music. "She dressed in a very theatrical style. She had lots of bracelets and a long cigarette holder and sunglasses and brilliant red hair in her 80s. She was every inch the actress."

Thus, when she bequeathed to her 12-year-old grandson a set of tails she had donned with a top hat in a cabaret-type production, it was somewhat par for the course for the colorful family.

Boris Thomashefsky was born in Ositniashka, a village in Ukraine, and raised in the neighboring town of Kamionka, where his grandfather was cantor. Following the family tradition, he got his musical start as a boy soprano soloist in the famous choir of Berditchev, the center of Jewish liturgical music in Russia.

Once, Tilson Thomas recalled, his grandfather's solo drew applause during a High Holy Day service. Though reprimanded for "disturbing" the service, the talented young boy quickly became a local celebrity.

Upon emigrating to this country with his family in 1881, he sang in New York City's Henry Street Synagogue choir, soon persuading Frank Wolf, a saloon-keeper and synagogue trustee, to finance the visit of a Yiddish company from London.

The tour is believed to have marked the beginning of professional Yiddish theater in America.

In 1882, while still a young teenager, Boris Thomashefsky produced and starred in the first U.S.-produced Yiddish play; because the "prima donna" did not show up, he played the female lead.

His wife, who was also born in the Kiev province of the Ukraine, immigrated to the United States with her family in the late 1870s, settling in a farming region in southern Maryland.

She was 14 years old and a seamstress when she first glimpsed him on stage in Baltimore. According to her memoirs, she told her brother-in-law Louis she wanted to meet the tall actor performing as a Chassid. Eventually, Louis invited the actor to dinner.

Boris Thomashefsky convinced her to become a Yiddish actress; the pair married shortly after her debut.

In their years together, the Thomashefskys produced three sons and a repertoire that ranged from hit musicals, comedies and American melodramas to classics such as Shakespeare — all performed in Yiddish. They introduced countless authors, composers, actors and singers to the American public.

Their work, Tilson Thomas said, "was about creating plays that were specifically designed to help Jews in America understand better the kinds of challenges they were facing in creating their identity here."

Many of Bessie Thomashefsky's plays addressed those challenges from a woman's perspective. She created, for example, original routines that were later copied and popularized by Fanny Brice and made known to contemporary audiences by Barbra Streisand in "Funny Girl" and "Funny Lady."

To this day, the Thomashefkys' adventurous spirits imbue the work of their grandson, who has been dubbed one of the most forward-thinking maestros in the world.

"Their attitude toward new and innovative things, toward exploring the avant-garde, as well as making the classics more accessible to a new audience, are very important themes that have continued in my own life and career," he said.

He not only sees their influence in his artistic choices but in his musical inflections.

"The idea of arriving at a take on a piece of music in the same way an actor arrives on a take on the character is very much derived from my grandparents' legacy."

That legacy, he believes, has broad lessons — about immigrant culture, Jewish life in America and the sacrifices sometimes required in realizing one's dreams.

The Thomashefskys, in coming to this country and becoming celebrities, "were giving up a secure sense of community living, a simple, predictable Jewish family life where there was already an answer to every question that could be asked," Tilson Thomas said.

Instead, they found themselves smack in the public eye, where they were subject to much adulation but also to crazed fans and relentless scrutiny. "People were totally obsessed with every detail of their lives," their grandson said. "When they were together, great. When they were not together, who were they together with?"

The fascination became especially apparent when the couple separated after several decades, and founded separate theaters. They wrote rival autobiographies, which were serialized to rapt readership in the two major Yiddish newspapers of the day, the Forverts and Die Warheit.

"In the morning, you could read Boris' version and in the afternoon, you could Bessie's version of the same story," Tilson Thomas said.

He attributes the separation to their strong temperaments, as well as to agents and promoters who hoped to profit from their appeal as separate headliners.

But though the Thomashefsky tale has its sad chapters, Tilson Thomas mostly regards it as an inspiring, amusing and triumphant story, with particular lessons for young people about the power of imagination.

The conductor also hopes the story will help bring the Thomashefskys' Old World hits, in all their humor and mordancy, back to life.

"I'm concerned that the tastes and the smells and the feel of Jewish life and Yiddishkeit life in America be preserved," he said. "I think it has a lot to teach us."