Keith Sieracki (Colorado Springs, Colo./U.S. Army) won a gold medal at 74 kg/163 lbs., the top U.S. performance at the Pan American Greco-Roman Championships in Caracas, Venezuela, March 14-15.    Held three of every four years during the non-Pan American Games years, the Pan American Championships features the best wrestlers in North, Central and South America.     Sieracki, a member of the 2001 U.S. World Team, won five matches, including a 6-0 victory over Cuban veteran Cecilio Rodriguez in the gold-medal match. Sieracki had beaten Rodriguez earlier in the tournament by a 8-1 margin.    U.S. wrestlers winning silver medals were Mike Ellsworth (Colorado Springs, Colo./Michigan WC) at  66 kg/145.5 lbs. and Jim Gruenwald (Colorado Springs, Colo./Sunkist Kids) at 60 kg/132 lbs. and Dremiel Byers (Colorado Springs, Colo./U.S. Army) at 120 kg/264.5 lbs. All three were defeated by Cuban athletes in the gold-medal finals.    Gruenwald, a 2000 Olympian, lost to veteran Roberto Monzon in the finals, 5-0. Ellsworth fell to World and Olympic medalist Juan Maren in the finals, 6-0. Byers, a 1999 World Team member, was edged by Miajian Lopez in the finals, 3-2.    Bronze medals were claimed by  Ethan Bosch (Colorado Springs, Colo./New York AC) at 84 kg/185 lbs. and Ross Thatcher (State College, Pa./New York AC) had a 1-1 record at 96 kg/211.45 lbs.    Placing fourth was Jeff Cervone (Colorado Springs, Colo./U.S. Air Force) at 55 kg/121 lbs.    Cuba won seven of the eight gold medals to win the team title. The United States was second, followed by Venezuela.