The commissions by the Library of Congress' Serge Koussevitsky Music Foundation are among the most coveted in music. They are part of the legacy of the great Boston Symphony conductor, who commissioned more 20th-century masterpieces than any other single person (try Stravinsky's "Symphony of Psalms" or Barto'k's Concerto for Orchestra as starters).

Last night's premiere, in the Coolidge Auditorium, was to have been a sextet for piano and winds by composer Walter Mays, a respected member of the music faculty at Wichita State University.

But it was not entirely to be. The program listed two movements -- "Elegy" and "Con forza," in that order.

When the members of Wichita's Lieurance Woodwind Quintet, along with pianist Robert Roux, appeared for the main event, horn player Nicholas Smith stepped forward to announce "a change in the program. What the composer has not yet finished," Smith explained, "is not what he wants to be heard. So we will play only one movement."

He said which one, but I couldn't make it out. However, if the aggressive, hard-edged music that followed was the Elegy, one waits in wonder to hear what the actual "Con forza" could "con"-tain.

What was played was one of those kenetic, percussive pieces that derives its effect from its accumulating momentum.

Mays was present to receive the applause.

The evening's finest music -- and it is a little gem -- was Danish composer Carl Nielsen's Quintet, Op. 43, in three movements. As with any Nielsen work that I have ever heard, its sureness of expression is unfailing; never does anything ring false, or seem like stuffing.

Unlike in the symphonies, Nielsen is not trying to say big things here. The most beautiful, and lengthy, part was the concluding set of variations. These are tiny little things -- lots of them -- of remarkable lyric and timbral range, and of the most consistent quality. Only a composer of this quality could bring off such a work.

The Lieurance Quintet, a fine group that always seemed meticulously prepared, also played Jean Francaix's urbane, breezy Quintet and some cheerful, if unexciting, dances by Ferenc Farkas.