Judith Jamison, artistic director of the Alvin Ailey American Dance Theater and formerly its electrifying star, slides onto a chair to watch the company rehearse. But she can't keep still.

As the dancers rocket around the Wang Center stage in Ulysses Dove's super-caffeinated work "Bad Blood" -- which will receive its local premiere at the Kennedy Center tonight -- Jamison's shoulders roll and her head bobs. She keeps time with one hand on her thigh, slapping out the rough, syncopated beat of a rambling Laurie Anderson song. Her whole upper body begins to shimmy and sway. It's as if, awash in the fierce energy of her dancers, she's been renewed.

"When you have a Stradivarius," she explains later, "you want to play it."

Jamison is fond of such grandiose comparisons -- she also likens her troupe, somewhat less elegantly, to a soaring C-5A cargo plane whose nose she endeavors to keep in the air. What her passionate remarks reveal is a nearly fanatic devotion to the Ailey company, and to the man who built it and changed the face of dance in this country.

"An extraordinary person passed this way," Jamison says. "I am here to make sure people know this."

Jamison's adherence to Ailey's vision is undoubtedly the reason the company is celebrating its 40th anniversary this year -- a benchmark many marriages don't even reach these days, much less arts organizations, and especially one that has sustained the loss of its founder. Ailey, who had AIDS, died in 1989, a brilliant but troubled man who nevertheless built up a primarily black company that became one of the most successful dance ensembles in the country.

Before the civil rights movement was up to full speed, the Alvin Ailey American Dance Theater was shining a spotlight on black achievement in theaters across the country. Before the big-name ballet companies ever graced the Kennedy Center Opera House stage, the Ailey danced at the center's opening, in Leonard Bernstein's "Mass" -- the only dance troupe to be invited.

The New York-based troupe was a showcase for Ailey's scintillating, hotly felt works, many drawn from his own experiences growing up poor in the South -- like the gospel-inspired, rafter-rumbling "Revelations," said to be one of the most performed dance works of this century. But unlike any other major modern dance company, it has never been solely a vehicle for its founder's own creations. It is also a repository of classic and avant-garde works from a panoply of choreographers -- pioneers like Katherine Dunham, Pearl Primus and Ted Shawn, as well as prominent contemporary dancemakers, many of them African American. Ailey took the repertory model that ballet companies had followed and made it work for modern dance, creating both a living museum and a bubbling caldron in which to create new works for the canon.

He put the company on the road for grueling tours, sometimes 49 weeks a year, by station wagon, bus and jet, making it the nation's most-toured dance company, surpassing even American Ballet Theatre. And this model -- carrying widely varying, accessible choreography to people in all pockets of the country and around the world -- still works, Jamison says.

"That declaration still has to be made: We are here," she says, beating the words out with her palm on the table. Dressed all in black with a flowing zebra-print scarf tossed across her shoulders, she's perched on the edge of a chair in her hotel suite -- slicing the air with her long-fingered hands, still refusing to sit still. "And this company will take dance wherever dance is needed, wherever it's necessary that that message be sent out that this is your art form, part of your culture."

Under Jamison's leadership, the company looks stronger than ever; its repertoire continues to grow. When the Ailey opens its five-day run at the Opera House tonight, it will perform two local premieres -- Dove's piece and George Faison's "Slaves" -- with others by Lar Lubovitch and Talley Beatty on subsequent nights, along with favorites such as "Revelations" and Faison's tribute to soul singer Otis Redding, "Suite Otis."

After years of deficits and fears of demise -- indeed, its 30th anniversary was celebrated under a shadow of debt -- the company closed its past season with a surplus. Tour dates are up: Since January, the Ailey has danced in 22 U.S. cities, and will continue on to Europe, South America and South Africa before its annual winter season at New York's City Center.

Here in Boston, where the company has performed for 30 consecutive years and where the streets are draped with "Ailey Week" banners, the dancers look improbably relaxed as they spread out on the floor backstage at the Wang, warming up long, snaking legs and supple spines.

"All of the things that Mr. Ailey set in place are still there," says Renee Robinson, who's in her 17th year with the company. "Miss Jamison is a different person, but she carries out her goals and desires in accordance with his."

Or as Jamison puts it, "I'm only carrying on his legacy." Given her flamboyance, it's somewhat ironic that this woman has so sublimated herself to her mentor. Jamison will be forever linked to Ailey -- as his muse and protege, his confidante, the crowning jewel in his finest creations, much as ballerina Suzanne Farrell was to New York City Ballet founder and choreographer George Balanchine. The searing and noble solo Ailey created for her, "Cry," dedicated "to all black women everywhere," established her as an icon of beauty, strength and power, assets that still carry heavy marketing value.

Jamison had ambitions of her own -- after 15 years with Ailey's company she left in 1980 to star in Broadway's "Sophisticated Ladies." She also ran her own company, the Jamison Project, for a year -- folding it when she took over the Ailey. She came back to the company just before Ailey's death for his final tour -- then, together with his mother and his longtime colleague Masazumi Chaya (now the company's associate director), held his hands as he died.

If Jamison has put her own stamp on the company, it has been in subtle ways: adding younger, technically dazzling dancers, acquiring sharp-edged choreography from such up-to-the-minute voices as Donald Byrd and the Urban Bush Women's Jawole Willa Jo Zollar, with more emphasis on the "dance" than the "theater" part of the company's name. A strikingly handsome, statuesque and charismatic woman, Jamison has been a profitable magnet for funders, and has raised the company's profile through her print and television ads for American Express and Tropicana.

Jamison's ambitions -- as large as her towering presence onstage -- have been channeled into keeping this pillar of the American dance scene flourishing. Among her current projects is the editing of a film to be aired on PBS's "Great Performances" series this fall, a documentary of her pulsating multimedia work called "Hymn," a tribute to Ailey with a libretto by Anna Deavere Smith, featuring a patchwork of fond recollections about the man.

And then there are her far-reaching visions for the future of dance. "Somehow concert dance has to be seen as on a par with everything else that's out there: sports, movies, popular music," she says. "We did an American Express commercial a few years ago that aired during the Super Bowl. More people saw us in that 30 or 60 seconds than have seen us in the entire existence of this company.

"It would be nice if 1 million people could see us again in an instant," Jamison says, folding her hands and settling back into her chair -- finally -- for effect. "We're still trying to put the word out that Alvin Ailey was a genius -- and he was speaking about you when he created this company." CAPTION: Judith Jamison on Alvin Ailey troupe's namesake: "An extraordinary person passed this way. I am here to make sure people know this."