Being a Russian ballerina in real life, and playing the part of a Russian ballerina in a vintage American musical comedy are two quite different things--the more so when, in a spectacular finale, the dancer must impersonate a nightclub stripper who gets shot dead at the climax of a hot duet. All this in view, it would be hard to imagine a woman better suited for such a combination by nature and background than Valentina Kozlova, the Bolshoi Ballet defector who took over the part of Vera Baronova in the Kennedy Center's revival of the 1936 "On Your Toes" last night. In looks, figure, facility and stage personality, Kozlova, to use that old Russian expression, has got what it takes, and as her debut last night plainly indicated, she knows how to take what she's got and use it to sizzling advantage.

Kozlova originally had been scheduled to join the cast, along with her husband Leonid Kozlov, in a week's time in any case, but her debut was moved up in the wake of the regrettable stage accident 11 days ago that left the show's first star, Natalia Makarova, with a broken shoulder blade (Starr Danias, Makarova's understudy, who has gallantly filled the role since the emergency, is back now in her original part of Lola). Kozlova's early entry into the show has found her in full readiness (she'd had considerable prior rehearsal), and she appears to have made the transition from classical ballet to pure show-biz as if to the manner born.

Unlike Makarova, Kozlova was not yet well-known in this country at the time of her casting in "Toes," though she'd certainly made a mark in the ballet world as one of the younger principals of the Bolshoi, where she danced leading roles in most of the traditional repertoire. Since she and her husband defected in 1979, they have broadened their repertoire considerably with works by contemporary Western choreographers, and this expansion may well have helped prepare Kozlova for her stylistic leap to "On Your Toes."

At any rate, she's taken it in stride. She makes her entrance in a boudoir scene in a flouncy pink peignoir, first throwing a temperamental fit over her Russian lover's philandering, and then seducing the "naive" Junior Dolan--an American vaudeville hoofer--into a dance atop her bed. Tall, blond, with a pinup's body and a face of patricianglamor, Kozlova had no trouble raising the humidity instantaneously, or sustaining the comical furor--her English, by the way, though distinctly Slavic in flavor, projects with fine clarity most of the time.

In the "Princess Zenobia" ballet spoof that ends Act I, she needed a taller partner than George de la Pen a, the splendid dancer-actor in the part of Morrosine (she'll be better matched, in this respect, by 6-foot-1 Leonid when he replaces de la Pen a on Tuesday). But in the concluding George Balanchine nugget, "Slaughter on Tenth Avenue," with Lara Teeter (as Junior) partnering, she was able to let out all her sexy stops, flicking a leg into the air like the striking of a match, and curling it around Teeter with deliciously insinuating languor. Makarova, who was very beguiling in the part, played Vera as a flamboyant vamp -- Kozlova is more a smoldering siren, in an interpretation no less individual or effective.

No one performer ever makes a show completely, and Kozlova is getting some wonderfully exuberant and polished help from other principals and the whole ensemble. Indeed, the whole pleasurable production, since I saw it last two weeks ago, zips along now with added crispness and vim, and the winning title number really builds to a socko pitch, as the audience is quick to note.