Brown voiced his support for the Global Warming Solutions Act of 2006, which requires California to reduce its greenhouse gas emissions to 1990 levels by 2020. Whitman, a former eBay CEO, has called for a moratorium on the law, which is still being implemented by regulators.
"The most important thing is to stay the course," Brown said of the legislation. "This is the future."
Brown's remarks came at a private fundraiser in Strawberry, which was attended by about 60 supporters.
In his brief remarks, Brown spoke about issues ranging from the environment to education to pension reform, emphasizing his experience as a former governor and mayor of Oakland, and as the current state attorney general.
In particular, Brown said his experience would help him nudge Democratic and Republican state legislators toward successful budget negotiations. If those talks failed, he said, he would look to California voters to help pass the budget.
"The key is to restore public confidence," he said.
Brown also threw his support behind the sale of San Quentin State Prison, prompted by a question from Assemblyman Jared Huffman, D-San Rafael, who backs that proposal.
"Turn it into an expensive, urban environment worth billions," Brown said. "It's not the most obvious place to put a prison."
Attendees at the fundraiser said they support Brown's agenda, with many saying his governmental experience is important during a budget crisis.
"Being able to address the state's fiscal situation in a manner that brings people together is going to be key, and Jerry Brown has the ability to do that," said Kerry Mazzoni, a lobbyist and former assemblywoman, state education secretary and Marin supervisorial candidate.
"We have in Jerry Brown an individual who has proven himself," said Richard Rubin, who hosted the fundraiser. "We can't afford this state to get more out of control than it already is."
A fundraising total for Sunday was not available.
Brown led slightly over Whitman in a survey released July 28 by the Public Policy Institute of California, out-polling her 37 to 34 percent with a 2.7 percent margin of error.
Marin County has 81,611 registered Democrats, compared with 29,020 Republicans and 32,242 independents. In the last governor's race in 2006, the county favored Democratic challenger Phil Angelides 48 to 46 percent over Republican incumbent Arnold Schwarzenegger.
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