The year 1978 was a good one for pianist Robert McDonald, and from his playing yesterday afternoon in the Phillips Collection, 1979 ought to be still better. Last year McDonald, a young pianist from Iowa via Wisconsin and Philadelphia, won the Friday Morning Music Club Competition here in Washington, and in New York City the Piano Teachers International Young Artists Auditions. His Phillips concert was a part of his Washington winnings.

For his first concert here, McDonald opened quietly with two sonatas by Padre Antonio Soler, refusing to let the disturbing noises of a child in the audience bother him. His absorption was total from the moment he began to play.

The seriousness of McDonald's entire approach to music and its performance was apparent from the character of his program. Following the Soler sonatas, he played Beethoven's "Les Adieux," the Chopin F Sharp Impromptu and Fantasie, the Third Prokofiev Sonata, and the Brahms-Handel Variations and Fugue.

Like one of his principal mentors, Rudolf Serkin, McDonald has little time for anything but the deepest purposes in music. His tone is designed to further the composer's intentions', and he proceeds without the slightest touch of appealing to any gallery except one of those who care about music as he does.

The Brahms was the crown of the day, warm in sound, massive, yet often surprisingly delicate. The Chopin Fantasie was as thoughtful. The one-movement Prokofiev came off with great fire, while remaining on the same high level of musicianship as the rest of the afternoon.