MEXICO CITY — He carried a briefcase in high school while his classmates were slinging backpacks. He rose up from a low-level functionary to become a powerful governor through the same attention to strategy he applies while playing chess.

Enrique Peña Nieto, Mexico’s president-elect, is as political an animal as they come, although he is an unknown quantity too, one with a smooth tongue and movie-star looks.

When his campaign was asked whom he considers his close friends, aides responded with a list of political power brokers and opinion makers he had met in the past year. None said they knew him well, but all spoke favorably.

In Mexico, the big question surrounding Peña Nieto is whether he represents the old ways of the Institutional Revolutionary Party, or PRI, marked by cronyism, or a break with the past, as he reassured voters during the campaign.

Peña Nieto began the transition to power on Monday, saying 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.

But the PRI faces an uphill fight in building political clout. It won only about 38 percent of the vote and is not expected to get a majority in Congress, with 96 percent of the vote counted.

Peña Nieto will have to deal with an old guard in his party that still has considerable power, a faltering economy, and an ongoing war against drug cartels. His closest rival, leftist Andres Manuel Lopez Obrador, who polled a higher-than-expected vote of about 32 percent, has refused to accept the loss, and many of his militant followers are suspicious of the results.

In Washington, the central concern is Peña Nieto’s position on the drug war raging across Mexico. He has spoken of his desire to reduce the bloodshed that has characterized President Felipe Calderon’s direct assault on traffickers, but he has also vowed to steer clear of the pacts with organized crime that were a part of the old PRI era.

‘‘The fight against crime will continue,’’ Peña Nieto said Sunday night. “Yes, with a new strategy to reduce violence and protect, above all, the lives of Mexicans. In the face of organized crime, there will be neither negotiation, nor truce.’’

He has not met President Obama but is said to have admired his 2008 campaign and borrowed some of the tactics, including a heavy use of social media.

The two men spoke on Monday as Obama called to congratulate the hemisphere’s newest leader.

Peña Nieto, 45, did not attend college or graduate school in the United States. But he was among a group of several Mexican boys who attended a year of junior high school in 1979 to learn English at Denis Hall School in Alfred, Maine.