MEXICO CITY — Mexico’s president-elect, Enrique Peña Nieto, began the transition to power on Monday, declaring that he would begin to name members of his cabinet in the next few days, and pledging to lead an efficient, transparent administration focused on defeating organized crime and improving the economy.

“The presidency that I want to enact and contribute to is modern, open to criticism, ready to listen and to work with all forms of political expression,” he said at a news conference here.

Standing in front of a banner that said “Mexico won,” he also said that he had spoken to President Obama this morning, and they had discussed how to “expand the relationship” between Mexico and the United States, especially in terms of economic integration.

His comments — in which he also reiterated that his government would make no pact or agreement with drug cartels — seemed designed to assuage fears in Mexico and the United States about both Mr. Peña and his party, the Institutional Revolutionary Party or PRI, which vaulted back to power on Sunday after ruling Mexico for decades with an autocratic grip. Arguing that he understood the changes that have come to Mexico since the PRI was booted from the presidency in 2000, Mr. Peña said he hoped to create “a democratic presidency that governs for all Mexicans.”