No doubt there are several perfectly practical reasons why the Vienna State Opera's "Ariadne auf Naxos" was put off until the final week of the company's engagement at the Kennedy Center. But there can be no better reason for it than that the production that comes last should be the Opera's very best.

And when that work is by Richard Strauss and Hugo von Hofmannsthal, this means opera of urbanity, sophistication and tender eloquence. In other words it means the Viennese style at its most refined.

First, there is the staging by Filippo Sanjust. No doubt, it cost the State Opera a tidy sum. The set for the prologue alone may well be more expensive than any American "Ariadne" production (including the Mets's or the curiously bland one brought here by Sarah Caldwell). In the Vienna version, the idea of a play within a play (or an opera within an opera) is carried to the opulent ultimate.

Next, there is the acting. It is not for nothing that one of the juiciest roles in the prologue is not sung. It is that of the Major-Domo, the manipulative figure who sets the action in motion. And in the Viennese tradition it was played to perfection last night by the noted Erich Kunz, now retired from his career as a leading baritone.

As for the singing, it was the first Vienna production in which the singers have risen with regularity to bravera brilliance. The strongest was Edita Gruberova as the wacky, irreverant Zerbinetta, a role notorious for its fiendish coloratura difficulties. Last night's was the first really satisfying performance of the role this listener has ever heard or seen. Her voice is light enough to handle the acrobatics but it is full enough to give body to the sound at all levels. Thus it never sounds frivolous. Her main aria was rewarded with the loudest ovation so far in the entire run at the Opera House.

Agnes Baltsa as the Composer was very much in the lauded Vienna tradition of this heart-rending music, as first sung in the 1916 premiere by none other than Lotte Lehmann.

The Ariadne was almost as thrilling. Once Gundula Janowitz voice limbered up, the noble sound filled the house, and her grasp of style was unquestionable. Among the other principals, Walter Berry's Music-Master went well, and only Josef Hopferwieser's cramped tenor as Bacchus reminded the audience of the vocal problems that have troubled earlier Vienna productions.

Presiding over it all was Strauss' protege Karl Boehm. The 85-year-old Boehm has been conducting "Adiadne" for 58 years, and it is perhaps the single opera with which he is most closely identified. Last night it was clear why.