The hardy Music of the Baroque is now embarking on its 20th season. Among the ingredients of its success are a top-notch, well-prepared chorus, an ensemble of brilliant instrumentalists, and a knowledgeable conductor who likes his music--anything up to Beethoven--fast and furious. Thomas Wikman's penchant for brisk tempi and bright orchestral color has its detractors, but it's the most sensible approach for Haydn's Lord Nelson Mass, the centerpiece of these concerts. Music of the Baroque's performances of this dramatic choral masterwork in seasons past were among the best I have heard. The music is conventionally given a pious and tepid treatment, but Music of the Baroque stressed its ferocity and stately grandeur, which culminates in a bracing sequence of militant fanfares. The remarkable trumpeters, Barbara Butler and Charles Geyer, are still with the group, and at last their virtuousity will be spotlighted in the Torelli Concerto for Two Trumpets. Sunday, 3 PM, United Church of Hyde Park, 1448 E. 53rd. Monday, 8 PM, St Paul's United Church of Christ, 2335 N. Orchard; 663-1900.