Australia's bicentennial was modestly but effectively observed yesterday at the Kennedy Center in Peter Sculthorpe's "Port Essington," a 1977 orchestral work depicting an unsuccessful attempt to establish a port on the northern coast of the continent in the early 1800s.

The Australian Chamber Orchestra, playing in a spiky, modern style, effectively portrayed the conquering bush, while a string trio, playing in 19th-century style, represented the settlers who never quite came to terms with the Australian environment. Otherwise, Schubert's Fifth Symphony -- very brightly played -- was the newest composition in a program beautifully focused on music of Mozart and Haydn.

The orchestra, small even by chamber standards, has more finesse than muscle, and its sound sometimes lacked full impact in the acoustics of the Concert Hall. It often plays without a conductor, though it takes tempos and cues from concertmaster Carl Pini. But in Haydn's Horn Concerto in D, excellent soloist Hector McDonald conducted when he wasn't playing. In three Mozart numbers, beautifully sung by Arleen Auge'r, Pini conducted in the standard mode.

In some of Verdi's arias, the feeling that the singer must struggle and strain to express everything in the music seems essential to achieving the proper effect. But in Mozart, even in such highly demanding arias as "Come scoglio" from "Cosi fan tutte" or the concert scena "Bella mia fiamma," K. 528, the singer must always try to make the singing seem effortless -- as natural as breathing. The voice should float from note to note, like a feather in a gentle summer breeze.

No singer active today is more adept than Auge'r at conveying that sense of ease in Mozart's music, and she managed it again yesterday, even with the considerable handicap of the Concert Hall's acoustics, which often are unkind to soprano voices. Her tone was sometimes glowing, sometimes glittering, always radiant; her diction and sense of style were exemplary: heroic and tragic in "Bella mia fiamma"; tender and intimate in "Non temer, amato bene," K. 505; and brilliantly lyric in "Exsultate, jubilate," K. 165 -- particularly in the final "Alleluia." There were more intimacy and a stronger impact when she sang in the Terrace Theater last season, but some of this may be restored when the concert is broadcast later on National Public Radio's "Music From Washington" series.

Jeffrey Kahane played the piano part in "Non temer," which Mozart composed for himself. It was a lavish gesture, hiring a pianist of such stature for such a brief passage, but the music is exquisite and Kahane played it exquisitely.