SACRAMENTO - Negotiations are intensifying between the Legislature and Gov. Arnold Schwarzenegger over an ambitious plan to reduce greenhouse-gas emissions in California.

Assembly Speaker Fabian Nunez said he expects to introduce amendments this week on Assembly Bill 32 -- which would make California the first state to impose pollution caps on industries to combat global warming.

The Democratic leader said in an interview that he intends to address the governance and enforcement concerns of environmentalists, business groups and the Schwarzenegger administration to pass the bill by the Aug. 31 close of the legislative session.

"This bill is going to be on the governor's desk," Nunez said.

Assembly Bill 32 aims to reduce California's global-warming emissions to 1990 levels by 2020 -- a 25 percent reduction on carbon dioxide and other heat-trapping gases. Last year, California was the world's 12th-largest producer of greenhouse gases.

The bill has been opposed by an industry coalition. But other business groups, environmentalists and political leaders have rallied behind the bill, raising the likelihood the Republican governor will sign it.

"I'm optimistic, and I think it's a great sign that all the leadership is engaged," said Ann Notthoff, California advocacy director for the Natural Resources Defense Council.

The bill, which is part of a package of green legislation moving through the Legislature, would phase in reductions to meet goals set by the governor last year.

Schwarzenegger, who is running for re-election, recently signed a state-nation global warming agreement with British Prime Minister Tony Blair to share information on solutions for reducing pollutants blamed for climate change.

"AB 32 could be an important tool in meeting Gov. Schwarzenegger's aggressive greenhouse-gas targets," EPA Secretary Linda Adams said. "I'm confident we can develop legislation that will support California's progressive approach to address climate change, economic growth and technological innovation."

Legislative staff members said they are close to working out a governance structure that's acceptable to all parties. Some of the changes likely will include emergency provisions that allow industries to lift caps only in case of extreme circumstances, such as a major supply disruption or natural disaster.

Right now, the bill directs the state Air Resources Board, which has a strong reputation for enforcement, to promulgate regulations for the mandatory reporting of greenhouse-gas emissions from several major industries, such as cement, landfills and utilities.

It requires state agencies to coordinate programs and encourage emissions-reduction technologies.

But the state EPA, acting on behalf of the governor, would rather see an umbrella board made up of agency heads.

Catherine Witherspoon, executive director of the Air Resources Board, said it doesn't make sense for her board to duplicate the job of other existing state agencies.

Witherspoon said the air board, for example, isn't the best agency to identify energy-saving and pollution-reducing remedies for the utility industry. She said that would be better left to the Public Utilities Commission.

Negotiators said the bill likely will be amended to include a mix of agency heads appointed by the governor as well as experts appointed by the Legislature.