He’s already been on the job a month, but that didn’t stop a packed Lehman Center for the Performing Arts and the city and state’s top officials from attending the formal swearing-in of Ruben Diaz, Jr., the 13th borough president of the Bronx last Thursday.

The 36-year-old former assemblyman won a special election on April 21 to succeed Adolfo Carrion, Jr., who cut his second term short by one year to take a job in the Obama Administration.

Diaz was toasted at the event by his colleagues in the state legislature, including Assembly Speaker Sheldon Silver and Senate Majority Leader Malcolm Smith, as well as Mayor Bloomberg and Governor Paterson.

Noticeably absent was Assemblyman Jose Rivera, the former Bronx Democratic Party Chair who Diaz and his political allies deposed last fall. Rivera’s son, Council Member Joel Rivera, who surprised political observers by withdrawing a bid to go toe-to-toe with Diaz for the borough’s top job, also did not attend.

Diaz, who spoke extremely well without any prepared notes at a recent gala for the Citizens Advice Bureau, seemed a tad flustered and more than a little excited at the swearing in, as he struggled a little with reading his speech from the lectern. 

The theme of the speech was “One Bronx,” which Diaz said was a vision his administration would outline in the coming weeks and months. But he listed the kind of Bronxites — in effect, every kind of Bronxite — who are a part of this vision: “young and old, regardless of your race, gender, religion, ethnic background or sexual orientation.”

Diaz emphasized economic development early in the address and the creation of “green” jobs. But the new borough president also said that equally important is creating “jobs for the people who live right here in the Bronx. For too long, our borough … [has] been the home to two, separate, very distinct economies, one made up of those with permanent jobs with benefits and a living wage, and the other comprised of those stuck in dead-end jobs with no hope for advancement.”

Diaz’s commitment to living wage jobs will be tested immediately as it is a central demand of activists lobbying for a community benefits agreement with the developer of the Kingsbridge Armory project, which has just entered the land use review process. Diaz could play a central role in helping to negotiate that agreement.

Alluding to a critical upcoming vote in the state legislature, Diaz addressed the issue of mayoral control of the schools (Bloomberg left before Diaz began his address). He said he had been a supporter of full mayoral control, but now believes parents, educators and students feel shut out.

“Those most affected by our school system must have their voices heard,” Diaz said. “I believe my appointment to the Panel of for Education Policy should have a stronger role in the decision-making process.”

The lively event also featured entertainment, including a number by seniors from the Casa Boricua Senior Center who brought down the house with a racy, salsa dance performance and a dazzling spoken-word performance by prodigy poet Nene Ali, age 10, who challenged adults to stop modeling bad behavior that they then blame kids for imitating.

Diaz is now borough president, but since he was elected only to complete Carrion’s term through the end of 2009, he will need to run again in the fall to be elected to a full four-year term.