At 80, Aaron Copland is an American institution, the venerable elder who defined our national character in sound. Because his music affirms a common bond, his presence is rightly treasured and no more so than when -- as on Saturday night with the National Symphony at Wolf Trap -- he conducted his own works.

Copland and the members of the NSO seem to have a special affection for one another. He has appeared with them off and on for more than 25 years and joined them in various celebrations. With directions as pointed and uncluttered as his music he urged them through Saturday's program, and they responded with spirit and precision, bringing to the familiar melodies of "Appalachian Spring" a particular tenderness. To that work and others concertmaster Miran Kojian and clarinetist Loren Kitt contributed expressive solo passages, following a forceful projection of the opening "Fanfare for the Common Man" by timpanist Fred Begun and the brass section.

Copland once wrote that composers do not necessarily make good conductors of their own music because they lack a "dispassionate heartbeat." His own conducting generally belies that contention, although Saturday night the closing "Rodeo" excerpts received a slower, more detailed treatment than was healthy for forward motion. However, when such an appealing offspring is involved, who can blame the creator for losing some objectivity?