WARWICK-No one seems to know for sure when the first concert was held at Pacem in Terris . . . not even its founder and continuting inspiration, Dr. Frederick Franck. The Shoestring, Pacem's newsletter, celebrates its 40th birthday this year together with its editor's 95th birthday. "I am not sure when Pacem precisely offered its first concert," said Franck, author of more than 30 books and countless numbers of noted art pieces. "I have a photograph with our present president Lukas, 10 years old, as a choirboy of Grace Church on 9th street and Broadway in New York City, whose choir gave a concert at Pacem in Terris in 1964. We were happy with this first musical position for him and his first acquaintance with high grade music, be it of the category known as "sacred music." To Dr. Franck all great music, be it ancient or modern, Byrd or Mahler, is sacred music and Pacem's first concert this year will trace its history as one of the most essential witnesses to Western culture by Louise Schulman's Ensemble in "early," or "ancient" instruments. This Sunday's program starts with works by Jacopo da Bologna, Italian, ca. 1350 and continues with works by Guillaume de Machaut, French (1300-1377), Guillaume Dufay, Franco-Flemish (1400-1474), Johannes Ockeghem, Flemish (1420-1497), Jacob Obrecht, Netherlands (1450-1505), Heinrich Isaac, Flemish (1450-1517), Heinrich Schutz, German (1585-1672), Dietrich Buxtehude, Danish (1637-1707). Louise Schulman s viola, built in 1520, is perhaps the oldest instrument used apart from the elegant human voice of soprano Margo Grib, who also plays the vielle and other ancestors of the violin as it still celebrates the spirit. The lute is played by Bill Zito, the viol and the viola da gamba by Jay Elfenbein. In this concert Louise Schulman, first viola of St. Luke's Orchestra and a highly reputed expert on ancient instruments will lead the ensemble. Margo Grib was soloist on the recording and world tour of "Einstein on the Beach" by Philip Glass and performs with New York's Ensemble for Early Music and the Long Island Baroque Ensemble. Jay Elfenbein is principal bassist and violon player with the N.Y. Collegium and Concert Royal and lutenist Recommended is an early arrival to secure a seat and enjoy exploring the many aspects of Pacem in Terris and its sculpture gardens. Pacem in Terris, a not-for-profit organization, is located at 96 Covered Bridge Road, Warwick. No advance reservations are available. Suggested donation is $8 for adults and $4 for children.