Ebrard, a political ally of former Mayor Andrés Manuel López Obrador, has supported his predecessor´s post-election challenges of Calderón´s legitimacy, though mostly from a distance.

On Monday he said his city government will accept "coexistence with the political reality of the federal powers" but "never complicity in the abuse that was committed last July 2," the date of the presidential election that López Obrador insists was fraudulent.

The mayor immediately staked out his differences with the federal government by opening his inaugural address with a promise to use city funds to provide coupons to poor Mexico City residents so they won´t have to pay a 1-peso per liter price hike on subsidized milk. The Fox administration imposed the new price on the Liconsa milk program in its final days.

"It was a wrong and unfair decision," he said of the price hike. The milk coupon program will have to be approved by the Federal District Legislative Assembly (ALDF), where Ebrard´s Democratic Revolution Party (PRD) enjoys an overwhelming majority.

The Mexico City mayor, officially the Federal District chief of government, is a highly visible position generally considered the second most important elected office in the Republic. Since capital residents won the right to choose their leader in 1997, both men elected to fill the post left early to run for president - Cuauhtémoc Cárdenas in 2000 and López Obrador in 2006.

Tuesday´s inaugural ceremonies at the ALDF chambers took place in a festive atmosphere free of the animosity and physical battles that marked Calderón´s swearing in at the Chamber of Deputies four days earlier. Assembly members of Calderón´s National Action Party (PAN) did walk out during a preliminary speech by ALDF president Víctor Hugo Círigo condemning Monday´s arrest of Oaxaca protest leaders.

The streets outside the ALDF building on the corner of Donceles and Allende were filled with cheering Ebrard supporters who listened to his address via speakers. Nearby, however, marchers from several activist groups blocked traffic along the Eje Central and other streets in protests not related to the inauguration.

Ebrard, 47, praised Cárdenas and López Obrador for forging a new style of government in the capital that emphasized social programs such as pensions for the elderly and scholarships for the poor, while simultaneously maintaining "fiscal austerity."

"That´s the way we govern on the left," he said.

But he also said he will move the city in new directions during his six-year term.

"Today a new era begins in the life of the city," he said. "The gains will be consolidated, but there will be new achievements ... that will solve the inequality that still prevails in the Federal District."

One of his first orders of business, Ebrard said, will be to create a city Constitution that will eliminate the last vestiges of federal control over the city.

"(With a Constitution) the Legislative Assembly will have its sovereignty and will be better able to protect the interests of the city government and residents," he said.

A former Mexico City police chief, Ebrard said he would seek 20,000 new police officers and use the community policing concept in their deployment.

"They will be better trained and operate in a culture of respect for human rights," he said of the officers. "And their performance will be evaluated and controlled by the citizens themselves."

Ebrard also plans to install 4,000 surveillance cameras on the capital´s streets, especially near schools.