VENEZUELA-Top Washington officials worry that Venezuela and Iran may be building more than economic bridges.They started with an agreement to build tractors, but Iran and Venezuela have quickly moved to oil, cement, homes, auto parts, shipbuilding and perhaps even nuclear energy. The new friendship between the two deeply anti-American governments was further cemented last month as Iranian Parliament speaker Gholam Ali Haddad Adel headed a delegation that visited Venezuela and drew expressions of support from populist President Hugo Chávez. ''It's a natural byproduct of their confrontation with the United States,'' said Armando Durán, a columnist and former Venezuelan foreign minister....