New York Times News Service

MEXICO CITY — With protests and little pomp, Enrique Pena Nieto on Saturday began his six-year term as president of Mexico, promising big spending and sweeping changes to bring peace and prosperity to a country troubled by drug violence and uneven economic growth.

“This is Mexico’s moment,” Pena Nieto declared in his inaugural address before a gathering of domestic and foreign leaders at the national palace, including Vice President Joe Biden, seated in the front row, while demonstrators kept far from the scene vandalized buildings outside.

Pena Nieto, 46, a lawyer who had been governor of Mexico state, has pledged to work closely with the United States to strengthen security and economic ties, which he believes would bring Mexico closer to a middle-class society and reduce the kind of drug war violence that has left tens of thousands dead in the past several years.

He made no promise to dismantle the drug-trafficking organizations, a focus of his immediate predecessor, Felipe Calderon. Instead, he unveiled a sweeping 13-point agenda focused more on domestic goals for crime prevention that would revise the penal code to attack impunity, give more attention to victims of violence, lessen poverty and hunger, improve schooling and even build new passenger train lines and expand Internet access.

“We are a nation that is growing at two speeds; some live behind and in poverty and others live in the developing part,” he said, alluding to new manufacturing plants and investments but also grinding poverty that affects half the population.

“There are a great number of Mexicans who live every day worried about the lack of employment and opportunities,” he added. “Those conditions also damage the image of Mexico abroad, and that is the Mexico that must be transformed.”

Still, his administration will be watched to see if it is propelling Mexico forward or backward.

Pena Nieto ushers in a new era for the Institutional Revolutionary Party, known as the PRI, which ruled Mexico for more than 70 years before the more conservative National Action Party toppled it in 2000 and again in 2006.

Pena Nieto and his associates say they represent a new, chastened party bent on promoting efficiency and economic change — there were no public inaugural celebrations — and promising to fight the kind of corruption long associated with it.

“It’s a very common misconception to think that the PRI’s return to power means the return of something that is already in history,” Luis Videgaray, who led the president’s transition team and is now finance minister, said in a recent interview.

“The PRI of today is like any other party: a party that competes in a democracy, that accepts results and understands that only through good government would it be able to compete again in elections,” he said.

Pena Nieto hardly begins with a mandate; he won 38 percent of the vote and faces a divided Congress. He recited the oath of office before Congress amid cheers and jeers, mostly from leftist legislators, and left the congressional chamber quickly.

Later, outside the national palace, scores of mostly young masked people clashed with police, set fires, threw rocks and vandalized hotels and stores along several blocks. More than 60 were arrested and several were injured.