For dancer Mikhail Baryshinkov, the first 30 years of life have progressed through a series of turning points, including abandonment of his native Russia in quest of artistic freedom; his emergence as a superstar, western-style, with American Ballet Theatre, and a first screening in a Hollywood movie not accidently entitled "The Turning Point."

Now the paths have led to still another crossroad: His debut Saturday afternoon with the New York City Ballet company, as Franz in the George Balanchine-Alexandra Danilova "Coppelia," a production of the ballet comedy originally unveiled here at the Saratoga Performing Arts Center in 1974, only weeks after Baryshinkov's defection from the Kirov Ballet in Canada.

By the time Franz's first solo fling arrived about 10 minutes into act one, anticipation was crackling through the air like static electrically. From his upstage corne, Baryshnikov bolted forward into the prescribed sequence of steps and leaps, coming to a knife-edged stop on one knee after a dazzling blur of pirouettes. The dam broke. The 6,000 spectators broke loose in yells and bravos.

The moment passed and the performance continued, but things would never be quite the same again. For Baryshnikov, it meant the start of a new phase of creative discovery under the tutelage of master choreographer George Balanshine; for the New York City Ballet, it marked the unprecendented absorption into their egalitarian ranks of an international luminary; and for Saratoga, it was another historic milestone to add to the town's already well-furbished stock.

Balanshine, in predictable fashion, had wanted Baryshnikov to "slip in quietly" into the normal New York City Ballet routine, without the hoopla that would undoubtedly accompany such an event in any other troupe. What Balanchine wants, Balanchine gets. Press releases prior to Saturday's matinee listed the casting for Franz only as "to be announced."

Though the usual leaks had spread the word here and there, the audience found out officially what it was in for by means of a mimeographed insert in the printed program. In the illustrated gallery of company dancers in the back of the book Baryshnikov, in his appropriate place, was described to wit: "Principal (since 1978)/Joined NYCB: 1978/Previous Affiliation: Kirov Ballet of Leningrad, American Ballet Theatre."

The Americanization of Baryshnikov seemed to be heading for the finish line. In mid-June, he had given his last performance with ABT, partnering his compatriot Natalia Makarova, as he had done in his U.S. debut four years earlier, in "Giselle." Now here he was squiring that most American of ballerinas, Patricia McBride, at an outdoor matinee in a state park. To boot, the audience was greeted by Ronald McDonald, a clown deputized by the hamburger sain (part sponsor of the afternoon's events) to ease the kiddies into the mysteries of classical ballet.

The afternoon before the debut, Baryshinkov rehearsed Balanchine's "Rubies" onstage with the company; early the next day he fretted over an injured knee and a sore tendon and was reportedly a bundle of nerves. During the first intermission of "Coppelia," though, word trickled from backstage that he was joking and chomping a wad of chewing gum, and that he'd been patted by Balanchine.

Afterward, in the company of friends, bubbly and carefree, he acknowledged that "Mr B." had said "Wonderful!" (the equivalent, for Balanchine, of a flood of superlatives) and kidded himself about a mistaken entry in the first act.

"I came on too early in the Mazurka without realizing it, and didn't know what to do next - I saw Balanchine in the wings looking at me as if to say what in the world are you doing there. It was such a stupid situation." Then he went into his by now perfected Balanchine imitation, screwing up his nose and saying, 'Next m-m-m and stripes'." The ballet is of course, Balanchine's "Stars and Stripes," but the word "Star" is beligerently excluded from Mr. B's personal vocabulary.

The performace of "Coppelia," as New York City Ballet performances go, was splendid, but only earthshaking in its sense of occasion. Patricia McBride was superbly shrewd and effervescent as Swanilda in a part that was created for her and fits her like a glove.

The soloists and corps de ballet evinced an extra measure of speed and energy, as if to say, see we're the same troupe we've always been, just putting our best feet forward - it's great to have "Misha" with us, but we can take superstars in our stride. Baryshnikov seemed to melt into the production effortlessly and naturally, scaling down th theatrics of his ABT performance of the role to suit the more simplistic conception of Franz the Balanchine-Danilova staging calls for.

The choice of "Coppelia" eased Baryshnikov into the Balanchine repertoire sideways, so to speak - the ballet is far from quintessential Balanchine and Baryshnikov was no stranger to the part. Later in the Saratoga run, he'll appear in Balanchine's "Jewels" and "Stars and Stripes" as well as Jerome Robbins' "Other Dances" and "Afternoon of a Fawn." The initiation has only begun.

The original production of "Coppelia" took place in Paris in 1870. That same year saw the construction of Saratoga's gambling casino - now a museum - where Diamond Jim Brady and Lillian Russell once led the fashionable rich to the roulette wheels and faro tables.

It's town that wears its past like a necklace, as the turrets, gables, spries, bays and porticos of its still-impressive Victorian homes testify. The racing season is still a month off, but Baryshnikov and the New York City Ballet gave the populace, native and tourist, an early touch of what it likes best - thoroughbreds.

Backstage Saturday night, Balanchine fussed over the choreographic changes he'd introduced into his "Vienna Waltzes," and clucked solicitously over Suzanne Farrell's entrance into the hypnotic final movement. At an earlier intermission break he replied, when asked whether the weekend had been everything he'd expected, "Yes, yes, was good, was good," smiling abstractedly the while. For Mr. B., it was just business as usual.