PARIS - Taking office as France's 23d president yesterday, Nicolas Sarkozy reiterated his promises of change as he assembles a streamlined, historically diverse cabinet, which is expected to include a prominent leader of the leftist opposition.

Sarkozy, 52, succeeded Jacques Chirac during an elegant ceremony at the Elysees Palace. Chirac, 74, who served two terms, greeted Sarkozy on a red carpet in the stone courtyard, then brought him inside for a 35-minute meeting during which Chirac turned over the top-secret codes to France's nuclear arsenal.

In his inauguration speech, Sarkozy pledged that he would reach out across ideological lines, an effort that is causing tensions among some of his lieutenants who fear they will be shut out of coveted cabinet posts.

"To all those who want to serve France, I say from the bottom of my heart that I am ready to work with them," Sarkozy said. "I will not ask them to deny their convictions. I will not ask them to betray their friendships. I will not ask them to forget their history. It is up to them to decide in their soul and conscience of free men how they want to serve France."

As the rituals continued with a 21-gun salute and an open-car ride escorted by a cavalry unit to the Arc de Triomphe, Sarkozy's aides resumed assembling a government described as a "dream team" that will shake up the traditional elite. The emerging picture of the cabinet-in-progress displays Sarkozy's taste for innovation, his political agility and his wish to create a hands-on, U.S.-style presidency, observers said.

Appointments will not be announced until later in the week, but key names and decisions were considered all but certain. The biggest surprise: Sarkozy has offered the foreign ministry to Socialist Bernard Kouchner, one of the most popular figures in French politics, according to political insiders and media reports.

Kouchner, 67, is a globe-trotting, bullet-dodging celebrity-politician who has aided victims of war and calamity as a founder of Doctors Without Borders, a humanitarian group that won the Nobel Peace Prize in 1999. He has served as France's minister of health and the U.N. governor of Kosovo.

He advocates foreign military intervention in defense of human rights, is considered pro-American, and was a rare French leader who did not oppose the war in Iraq.

Sarkozy is likely to reorganize the foreign ministry to let Kouchner focus on Africa, Asia, and humanitarian and human-rights questions while the president takes the lead on dealing with the United States, Europe and other big powers, analysts said.

But unlike previous presidents, who delegated domestic policy to their premiers, Sarkozy is overhauling the governmental structure to more directly involve the president, according to Thierry Vedel, an expert at the Center for the Study of French Political Life.

Chirac did not speak in leaving the Elysee. He is expected to create a foundation for sustainable development and environmental issues to capitalize on his international reputation, according to the Associated Press.