Rather oddly, neither of New York's opera companies scheduled ''Don Giovanni'' for its anniversary year. Prague is celebrating it, and Salzburg has mounted and recorded a glossy version, but New York has had only the film ''The Mozart Brothers,'' about a perverse avant-garde director, and a Peter Sellars production at the Pepsico Summerfare Festival.

For all regular operagoers, though, ''Don Giovanni'' and the characters who people it are a constant presence. Almost all the great singers of the past 180 years have sung in it at one time or another. The understanding and the relative prominence of the principal roles have undergone surprising shifts over the years; that fluidity is one measure of the piece's staying power.

Leporello has always been the easiest role to put across, if hardly the easiest to do really well. The grubby, ill-used, constantly commenting servant has appealed to all the great character basses, as Zerlina has to all the sweet type of lyric sopranos (and sometimes mezzos). For many years Zerlina's name came first in the starry cast lists, especially when Adelina Patti sang it (Verdi admired her in the role).

That has not been so for a long time, but Don Ottavio is the part most in eclipse currently. Bold-voiced tenors are no longer taught to sing the runs and scales he must command. The potency of the Giovanni figure and Donna Anna's repeated reticence toward her nominal lover, Ottavio, conspire to put him in an equivocal position dramatically. It doesn't help that when he sings both of his arias (Mozart wrote them as alternatives), one of them is weakly placed. But Mario, Rubini and the other bel canto tenors all had triumphs in the part, and Wagner pointed to a triumph of another sort when, after poking the usual fun at the emptiness of Meyerbeer's music, he sang Ottavio's air (one would love to know which) for his wife. ''There is real melody,'' he said - ''at once you are in contact with a human being.''

Donna Elvira is in the ridiculous position of a rejected, importuning mistress who hopes on; commentators who want to emphasize the ''dramma giocoso'' side of the opera emphasize her silliness. ''We know at once that we are not going to be allowed to take Elvira seriously for a moment,'' wrote the great E. J. Dent. In some times and places hers has been considered a secondary role in the opera. And Mozart wrote no music more sublime than for her. ''Seriously'' is not quite the word for how we take her, but if our hearts are not pained, something has gone badly wrong.

Donna Anna has the grandest part, and the longest. The whole opera turns on the efforts to punish Don Giovanni for his attempted violation of Anna and his murder of her father in the first scene. The great question about Anna - asked at least since the romantic E. T. A. Hoffmann first offered his answer - is whether she covertly desires Don Giovanni (Hoffmann thought so), and indeed whether she is perhaps lying about what took place between them at the beginning of the opera.