RIO DE JANEIRO, Apr. 29 - In a rebuff to the Bush administration's efforts to press Latin America to take a tougher stance on Cuba and Venezuela, a Chilean Socialist emerged Friday as the consensus choice to become secretary general of the Organization of American States. The O.A.S. is scheduled to convene in Washington on Monday to formally elect the Chilean, Interior Minister José Miguel Insulza, 62. His opponent, Luis Ernesto Derbez, the Mexican foreign minister and Washington's favored candidate, withdrew Friday afternoon after negotiations in Santiago, Chile, that involved Secretary of State Condoleezza Rice and several of her South...