On rare occasions an artist is able to step so totally inside the music that the artificiality of performance dissolves and art becomes life itself. Such was the case at the National Symphony concert last night with Maureen Forrester and Mahler's "Das Lied von der Erde."

This is, of course, a work that Forrester, one of the finest Mahler interpreters, has made a part of her life's blood. She makes every phrase resonate with the faith and despair as well as joy and terror that prompted Mahler to compose this most personal of statements.

Her voice is a many-colored instrument which can resound with triumphant power or diminish to a whisper of resignation. She found the most delicate, hesitating articulation to convey the tentative, innocent world of young love suggested in a few lines of the poem on beauty. In the coloring of the single word "Liebe" -- "love" -- she evoked the whole cycle of pain and loss. Her singing of the final section, "Der Abschied" -- "The Farewell" -- was charged with a poignant longing which found its bittersweet release in the final "ewig."

Also singing in the Mahler work was tenor Seth McCoy, whose warm, full sound was glorious to hear but no expressive match for Forrester. Though phrases were beautifully shaped, McCoy failed to find the work's deeper emotional levels.

Although the orchestra as a whole under guest conductor Robert Shaw was not in its most inspired form, the various soloists within each section were, producing one radiant passage after another. Oboist Sara Watkins, particularly in the final section, played with great expressiveness, as did flutist Toshiko Kohono. Both also did a superb job, as did the other woodwin soloists, in the Hadyn symphony that opened the program. John Martin's cello lines were a lovely complement to Forrester's singing, as was a brief solo by concertmaster Miran Kojian.