The Montgomery Performing Arts Society recently proved that people who know and care about what they are doing can make any obstacle seem small.

In rapid succession they lost their opening night performance to snow and their leading make singer to laryngitis, but they did not miss a step. The first performance of Lerner and Loewe's "Brigadoon" at Montgomery College in Rockville suddenly became a full dress rehearsal, with Robert Judson filling in as Tommy on a day's notice.

The society's humility in changing the billing was commendable but not necessary. What the audience got was first-class amateur theater, the kind many professional could learn from. Although the solo roles ranged from adequate to superb - Glenda Stroup was a stunning Fiona - it was the ensembles that carried the show. Beautiful yet simple costumes, elegant choreography and solid orchestra all helped to heighten the effect.

My only real complaint about the production is that the sound system created uneven volume for both singing and speaking, and often garbled the words. The polish and joy shown in the performance, however, made this problem seem small, and made the evening most enjoyable. The Montgomery Performing Arts Society hopes to present another production in June which should be well worth keeping an eye out for.

For information on the two remaining performances of "Brigadoon," Saturday at 8 p.m. and Sunday at 3 p.m., call 762-8619.