The Ballet West we saw at the Opera House last night was the same company we saw there two years ago, when it became the first classical troupe from the yonder half of the nation to be seen at the Kennedy Center.

Then again, was it the same? Somehow it looked spankingly fresh, born again, so to speak, into a new vivacity and awareness of its own appeal. It was an impressive company the first time around, when it presented a fine full-length "Swan Lake" and a repertory bill. At the same time, there remained a faint whiff of the classroom about it, an aroma of lessons, well learned but still lessons.

This time, again, the company is presenting a repertory program -- the one that opened its week-long visit last night -- and an evening-length ballet, the long-awaited East Coast premiere of the restored Bournonville work "Abdallah," which bows tonight. What's new is that these dancers now seem to have complete possession of themselves and their audience, even when, occasionally, the dancing falters. I don't mean to say the dancing is deficient, or that the company is merely good at covering its tracks. The dancing was splendid in 1983, and although there've been changes in personnel -- mostly, younger dancers rising in rank -- it's still splendid. But these performers have learned something besides good dancing in the interim -- they've learned how to dance as if they mean it, and to project this conviction way beyond the footlights.

Ballet West, hailing as it does from Salt Lake City and serving an area many states wide, may still be a "regional" company, but it's lost the regional look. It's a class act now, and that's a vast tribute to artistic director Bruce Marks (who soon moves on to head the Boston Ballet), as well as to principal teacher Toni Lander Marks and all their colleagues.

You know someone is doing something right when you see a "Les Sylphides" as enchanting and refined as the one Ballet West staged for openers last night. This venerable Fokine warhorse palls so easily. It takes two essential things to avoid making it look like a fossil -- a mastery of style, and dancers who believe utterly in the moonlit romanticism the ballet was designed to evoke. This performance had both. From the "Nocturne" on, one could see it in the floating arms, the sweetly tilted heads, the rounded wrists, the delicately wafting feet and the fluent phrasing of the whole cast. In "Les Sylphides" such things aren't picayune details -- they are the ballet. The feathery and exceptionally musical Mary Ann Lind did stand out somewhat from the rest, but this was very much an ensemble performance, individuals melting into a poetic unity. A tasteful variant arrangement of the Chopin score, and the sensitive conducting of Varujan Kojian -- who dared to be leisurely, but never soupy -- also added to the effect.

In the succeeding "Corsaire" pas de deux -- another standard that readily fizzles -- some of the fireworks did misfire, but not the underlying spirit of combustion that is really what raises the roof. Bruce Caldwell hurled himself into the duet with a bold, he-man approach, and any thought of unsteady pirouettes vanished with his spectacular leaps and heroic partnering. Lee Provancha Day had moments of wobbly footing, but they seemed trifling next to the grand regality and panache of her solo variation.

In Marks' "Lark Ascending," created in 1977 to a violin and orchestra score by Ralph Vaughan Williams, the dancing perfectly matched the choreography, perhaps partly because this lyric and sculptural piece was made expressly for the company. In any case, Lisi Gotaas affectingly exploited the work's metaphoric imagery of flight and song, with excellent support from five men. The style of the piece reflects Marks' dual background -- in modern dance and classical ballet -- without calling attention to the fusion. In its own terms, it's a beautifully crafted dance, and it deservedly won Gotaas a personal ovation.

The concluding ballet was George Balanchine's "Western Symphony," performed here on the second anniversary of the great choreographer's death. Once more, it was the overall rip-snorting, bawdy spirit of the performance that accounted for its success, rather than outstanding individual contributions. The swaggering of the men, hands gripping belts, and the saucy hip-tossing of the women of the background ensembles were as eye-catching as any of the virtuoso turns from the soloists. Among the latter, one might single out Lisa LaManna and partner Edward Farley in the opening "Allegro," and Junoesque Suzanne Wagner, twirling her legs over the head of William Pizzuto in the finale, as especially apt. John Boyt's wonderfully suggestive set -- like the ballet itself, more a tribute to the movie western than to any real, historical West -- and Karinska's matching costumes, both from the original New York City Ballet designs of 1955, proved as captivating an enhancement as ever.