Leventhal's career in government began in 1967, when he worked at The Pentagon in the office of the General Counsel of the Air Force. He remained in Washington to work as an assistant to the executive director of the Equal Employment Opportunity Commission, which had recently been established by the civil rights act in 1964. In 1969, he moved back to New York City to work for the administration of Mayor John V. Lindsay as fiscal director of the human resources administration, then moving to the mayors office to become assistant to the mayor and then City Hall Chief of Staff.[4] In 1972, Lindsay appointed Leventhal, then 29, as Commissioner of Rent and Housing Maintenance.[5]
After serving briefly in 1973-74 as chief counsel to the US Senate subcommittee on administrative practice and procedure, chaired by Senator Edward M. Kennedy,[6] Leventhal practiced law in New York City for four years, becoming a partner at a law firm, Poletti Frieden Prashker Feldman and Gartner before returning to city government in 1978, when newly elected Mayor Edward Koch appointed him Commissioner of Housing Preservation and Development.[7]
In August 1979, Mayor Koch implemented a major reorganization of the City Hall staff in a move whose scope "stunned" City Hall observers and appointed Leventhal Deputy Mayor of Operations, with all city commissioners reporting to Leventhal; previously all commissioners had reported directly to Mayor Koch.[8] As deputy mayor, Leventhal was responsible for overseeing the day-to-day operations of City government, including implementing a government-wide productivity program. Included among the productivity initiatives overseen by Leventhal was the first New York City "gain-sharing" program where, in return for reduced manning requirements, sanitation workers performing more work shared in the budgetary savings in the form of incremental pay.[9] Leventhal also suggested to Mayor Koch that the city move to a GAAP balanced budget a year before the State law required, a move widely praised in the press and the financial community and which led to the restoration of the city's investment-grade rating.[10] After leaving his post in 1984, to assume the position of President of Lincoln Center for the Performing Arts,[11] Leventhal was the subject of New York Times editorial, which noted that Mayor Koch had run on the slogan "why not try competence" stating that Leventhal "supplied much of it" providing "invaluable services for his community" and "departs City Hall with its gratitude."[12] Similar comments were also made in the New York Post, stating he performed his job with "surpassing style and skill."[13]
Leventhal's hiring as president of Lincoln Center was recommended to its board by Chairman Martin E. Segal, a cultural leader of New York City over many decades.[14] Together with Segal and his successors - George Weissman, former CEO of Philip Morris and operatic superstar Beverly Sills - Leventhal focused on overseeing a significant expansion of Lincoln Center's programming activities including the establishment of a new jazz program, hiring the then-26 year-old trumpet virtuoso Wynton Marsalis as its artistic leader, eventually culminating in the creation of a permanent constituent organization, Jazz at Lincoln Center; launched the Lincoln Center Festival, an eclectic gathering of cutting edge performances from around the world; created Lincoln Center's American Songbook series, a tribute to the golden days of American popular music; and started Midsummer Night Swing, a populist informal program of dancing open to the public on Lincoln Center's central plaza.[2] While these initiatIves were generally well received, they occasionally elicited criticism from Lincoln Center constituents that Lincoln Center’s expansive programming was competing with their own programming and fundraising efforts. [15]. Nevertheless, during his tenure, there was also unprecedented cooperation in programming among Lincoln Center and its constituents, most evident in the Mozart Bicentennial celebration of 1991/1992, in which all constituents joined in performing all of Mozart's compositions.[15]
Leventhal also supervised the construction of the Samuel P. and David Rose building, the first new building since Lincoln Center's creation which, among things, included the first dormitory facilities for the Juilliard School and the School of American Ballet (which had become the first new Lincoln Center constituent company since its founding); a year-round performance facility for the Film Society of Lincoln Center; and rehearsal, studio and office space for Lincoln Center and its constituent companies.[16] Together with Chairman Beverly Sills, Leventhal launched what would become a $1.2 billion Lincoln Center redevelopment program, securing a $250 million grant from New York City to start the project. He and Sills were also instrumental in receiving New York City's commitment to have the developer of the future Time Warner Center include provisions in his plan for a new Lincoln Center performance space.[17]