Every year Wolf Trap uses as the backbone of its opera company a very select crowd of singers -- usually about a dozen -- who are shooting for the top. Some will make it and some will not, and one of the best times to assess them is in the annual showcase concert near the end of the summer season, held yesterday at the Filene Center.

This listener is not about to try to say who in this group will succeed; there are too many imponderables -- both, it must be admitted, in the courses of their careers and in the perceptions of the listener.

One thing is sure, however. This year's crop is one of the very best. They were selected from among 700 applicants -- 350 of whom were auditioned. And each one of those who made it this season is promising and several have advanced beyond promise.

Yesterday's program went beyond convention in another way as well. There was not a note by Verdi, Puccini or Wagner. They are true giants, but it's nice to get away from them once in a while.

The program was dominated by bel canto opera and by Mozart (I am firmly convinced that Mozart had the greatest musical mind in history, but hearing different composers is refreshing).

As for the singers, the most fascinating of them was 31-year-old Allan Glassman. He used to be a baritone and was quite familiar as such to Washington audiences. But last year he became a tenor -- high C's and all.

At this point, he is a very gifted tenor. It is a light voice -- but it clearly was the one most alluring to yesterday's audience (tenors have a way of doing that, which may in part explain Glassman's switch). It sounds beautiful, and Glassman should be careful not to work it too hard (no Radames!).

His finest moment yesterday came in that extraordinarily exposed duet, "Au fond du temple saint" from Bizet's "Les Pecheurs des Perles." Glassman simply could do no wrong. And though baritone Ned Barth was fine, he was supportive.

Another quite polished performer was soprano Dawn Upshaw. During the lengthy concert she was the first one who made your ears perk up, as Konstanze in Mozart's "The Abduction From the Seraglio," a part so grueling that some sopranos must sometimes wish that Salieri had come out on top in historical perspective instead of Mozart. Upshaw has impressive control, and the voice has a lustrous glow that lends it special distinction.

In an excerpt from "Don Giovanni," she also was a stylish Zerlina to the Don of Gordon Hawkins, the bass from Southern Maryland who almost became a major-league pitcher instead of a singer. He is not yet a Don of great presence, but that voice is as beautiful as ever, and he is developing as an actor.

Another singer in the concert whose career seems well-advanced is soprano Phyllis Treigle (she's the daughter of the late, great bass Norman Treigle). She had several fine moments, but the loveliest was as Rosalinde in excerpts from Strauss' "Die Fledermaus" (I had not heard this music in a while, and was newly bowled over by its utter perfection).

Among the other able singers: mezzo Luretta Bybee, tenor Richard Croft, baritone Richard Paul Fink, soprano Barbara Kilduff, bass David Langan, mezzo Victoria Livengood, baritones Robert Mattern, James Michael McGuire and Eugene Perry, soprano Rachel Rosales, tenor Darren Keith Woods.

Also, at the concert, there was a degree of rapport in the ensembles ending each section of the program that one does not recall from previous Wolf Trap showcases.

Richard Woitach, Stephen Crout and Stephen Sulich conducted.