Joe Privitere (Binghampton, N.Y.) won a silver medal at 152 pounds at the FILA Junior World Greco-Roman Wrestling Championships in Nantes, France, July 5.    The Junior World Championships feature the best wrestlers in the world ages 17 to 20 years old  (born between 1980-1983).     On Wednesday, Privitere opened with an 8-4 victory over Hristov Lachenar of Belarus, in the semifinals. In the gold-medal finals, he was defeated by Voldoymr Shapskykh of Ukraine, 6-0.    It was an outstanding performance by Privitere, who was representing the United States at an age-group World tournament for the first time. For the competition, he registered a 4-1 record. Privitere competes for the Univ. of Binghampton, and was a high school star at Johnson City High School in New York.    Final placements of the other U.S. wrestlers were unavailable at press time. However, organizers indicated that Andy Bowlby (Corvallis, Ore./Orange Crush) placed seventh at 286 pounds.     The Greco-Roman coaches are Dan Russell of Gresham, Ore.,  a coach for Team Excel and Ike Anderson of Colorado Springs, the National Greco-Roman Developmental Coach.    The women's freestyle competition began on Wednesday, July 5, and the men's freestyle competition begins Thursday, July 6.    A web page has been developed by the tournament organizers at http://www.lutte-2000.com      FILA JUNIOR WORLD GRECO-ROMAN CHAMPIONSHIPS at Nantes, France, July 5    U.S. performances    69 kg/152 lbs. - Joe Privitere, Binghamton, N.Y. (Univ. of Binghamton), 2nd place    Wednesday's matches    Semifinals - dec. Hristov Lachenar (Belarus), 8-4    Gold medal finals - lost dec. to Voldoymr Shapskykh (Ukraine), 6-0    Tuesday's matches    dec. Ivan Kron (Switzerland), 3-0; dec. Yoki Snao (Japan), 6-2; dec. Selahattin Gungor (Turkey), 8-4