The select 21-piece nucleus of the Boston Symphony Orchestra, directed by Hernard Z gave a program this week, flavored on the modern side in contrast to the all-Mozart program of last week. The opening and closing selections--both 20th century arrangements of 18th century compositions--furnished an interesting contrast between the idioms of the two centuries, and between different methods of arrangement. adaptation of a harpsichord suite by Dominico Scarlatti left the original melody and harmony unaltered, merely adding drum, tambourine, triangle, and xylophone to the traditional 18th century orchestra. Even those additions did not alter the character of the composition markedly, for these tinkling and rattling instruments gave an orchestral approximation of the harpsichord tone.

Stravinsky's arrangement of a suite by Pergolesi, by contrast retained only the form and melody of the original, progressively adding more and more idiom to each of the eight dances. There was, however, within the movements, considerable alternation between the two styles, the softer and slower passages being nearly pure Porgolesi, the louder and faster passages principally Stravinsky. There were the typical Stravinsky cross-rhythms, two against three, throbbing dissonances in the trombone and basses, mechanically repeated figures for pizzicato strings, and, at the end, circus-style trombone "smears" for satirical effect.

The orchestra's ambitious attempt to perform Schubort's 5th Symphony with only 19 pieces was highly successful, the lighter tone making the texture clearer than in the more usual large-orchestra version. Mr. Zighera controlled the dynamics masterfully and the individual players handed the theme back and forth with a team-work essential to a small ensemble. There were not enough violins, however, to balance the rest of the orchestra, as their enunciation of themes was occasionally smothered by the other instruments.