California State Assembly
In 1962, Warren ran for office in the 56th Assembly District, first winning the Democratic primary and then defeating incumbent Chet Wolfrum in the general election, becoming the only Democrat to beat an incumbent in that year's California legislative election. He was to serve 14 years in the California State Assembly, from 1963 through 1977. The district he represented included the areas of Hollywood and Wilshire; after redistricting it was renumbered, becoming the 46th Assembly District.
In the Assembly, Warren became known as a strong proponent of environmental initiatives, but environment was not among his main interests at first. As the representative of an urban area, his initial legislative focus areas included fair housing, other civil rights matters, and transportation. Air quality was also a concern for his district, where smog was a problem. Early in his legislative career, he was the Assembly's representative to the Governor's Advisory Commission on the Status of Women. That experience led to his becoming author of several bills aimed at ensuring pay equity between men and women performing the same jobs. Four years of effort led to the successful enactment of one of his bills, AB 22.
He initiated and developed the first U.S. statewide 9-1-1 emergency telephone service program. Warren's efforts led to Governor Ronald Reagan being persuaded to impose a 0.5% surcharge on telephone bills to fund the program, in spite of having promised not to raise taxes. Reagan signed the authorizing legislation, known as the Warren – 911 – Emergency Assistance Act, into law in 1973. The state system, which cost some $137 million and took more than a decade to implement, was scheduled to be completed in 1985.
In 1973, Warren was chairman of a State Assembly subcommittee charged with addressing issues of future energy demand in California. In that role, he developed what he described as a "consuming interest" in the topic of energy. This led him to draft AB 1575, an innovative bill that proposed creating a new state energy agency to make independent forecasts of electricity demand, enforce energy conservation, and encourage the development of alternative forms of energy. A modified version of the legislation passed in both houses of the legislature, but Governor Ronald Reagan vetoed it. Just days after the veto, the start of the Yom Kippur War in the Middle East led to the Organization of Petroleum Exporting Countries (OPEC) imposing an oil embargo that created the 1973 oil crisis. The oil crisis caused Reagan and his staff to recognize the need to reexamine government energy policies.
Warren's bill AB 1575, known as the Warren-Alquist Act, was enacted in May 1974. It established the State Energy Resources Conservation and Development Commission, later known as the California Energy Commission. In later years, Warren described the law as the "first successful effort by any [U.S.] governmental jurisdiction to deal with the energy problem in any of its aspects." Following the law's passage, the National Conference of State Legislators established a committee on energy policy and Warren became its first chairman.
Warren was one of the principal authors of the Coastal Protection Act of 1976, which established the California Coastal Commission as a permanent body upon the expiration of the four-year authorization for the Coastal Commission created by Proposition 20 in 1972.
Reminiscing during oral history interviews in the 1980s, Warren commented on his unexpected status as a successful environmental leader:
Among a small circle, I became a minor celebrity and received credit which I did not deserve for things which I did not fully understand. I was considered an environmentalist, but I'm not sure I was deserving. Certainly I had environmental concerns, but I'd given such concerns only limited thought and attention.