Without question the outward trappings are formal, with all those tuxes, long black dresses and a conductor beating time on the podium. But, as such things go, the atmosphere is comparatively informal. Which may be one reason the Utah Symphony's annual New Year's Eve concert has turned into such a success - i.e., the audience feels part of both the music and the program.

Thus at Monday's edition, before launching into the last of three Fritz Kreisler bonbons, music director Joseph Silverstein (here on the violin) took time to dedicate it to a young couple who had become engaged that very night. (The title, appropriately enough, "Liebesfreud" - "Love's Joy.") Nor was the audience afraid to come in with the traditional clapping in Johann Strauss Sr.'s "Radetzky March," or drown out the postlude to the "Blue Danube" Waltz (Johann Jr.) when, for the first time in memory, Silverstein went past the point at which 1990 became 1991 - i.e., midnight.Before then he and the orchestra served up their now-familiar Viennese sampler - music of Mozart, Nicolai, Weber, Suppe and the Strauss family - in vigorous fashion. Whether in the jubilant stirrings of the Overture to "The Marriage of Figaro" (Mozart) or the overtures, waltzes and polkas that followed, performances were spirited if a trifle heavy in sound, with a decided emphasis on the low end.

That meant a not-so-delicate "Merry Wives of Windsor" Overture (Nicolai) and a solid-sounding "Roses From the South" (Johann Jr.). At the same time Silverstein brought a semi-deliberate Viennese lilt to the latter, with some real Schwung at the climax, and a welcome energy to the same composer's "Fledermaus" Overture, perhaps the perfect New Year's Eve piece.

That same lilt was evident in Weber's "Invitation to the Dance," here in the Berlioz orchestration with its haunting cello solos and vividly projected woodwind writing, and the lovely waltz theme of Suppe's Overture to "The Beautiful Galathea," which came in for an otherwise rousing performance.

The second half brought a chamber orchestra conducted by Kirk Muspratt in the three Kreisler pieces, with Silverstein the not-always-on-the-money soloist. Still, the music's sentiment came through, whether in the nostalgic "Caprice Viennois" or the fragrant melancholy of "Liebesleid" - "Love's Sorrow."

Then, with Silverstein back on form (and on the podium) came the all-Strauss finale, spiced by a few noisemakers in the audience and the musicians themselves wearing party hats (including a number of gentlemen in tiaras). Although the performance itself seemed a bit laid-back, the clapping lent the "Radetzky March" an appropriately martial air. And although the strings in the "Pizzicato Polka" seemed a mite thick, they registered brightly enough.

After which Johann Jr.'s "Perpetuum Mobile" whirled merrily by, Silverstein capping things Viennese style with a spoken "Und so weiter" - here "Etc., etc." But that same momentum helped build a nice head of steam in a pair of polkas, Eduard Strauss' "Bahn Frei" - "Clear Track" - and Johann Jr.'s explosive "Thunder and Lightning." And if the concluding "Blue Danube" seemed less expansive than of yore, well, perhaps the conductor had not only one eye on the clock but the other on the horns and kazoos in the audience.

After all, at midnight it became their concert.