South American leaders face intense disagreements as they prepare for a regional summit in Argentina.Colombia’s Alvaro Uribe is under fire for plans to allow the United States increased use of seven military bases in his country. Washington and Bogota insist it will help the fight against drug trafficking and left-wing rebels. But critics, led by Venezuela’s Hugo Chavez, denounce it as ‘imperialist aggression.’ The deal would let US aircraft operate from the seven bases, but would not permit an increase in military personnel. The plan has raised diplomatic tensions in South America. Many leaders are wary of an increased US military presence, recalling Washington’s support for right-wing dictatorships in the past. The White House denies any intention of establishing a permanent American military base in Colombia. But President Chavez said greater US involvement in Colombia could presage a stab at Venezuela’s huge oil reserves, and could even spark a regional war.