If the Board of Supervisors approves the legislation, new residential and commercial buildings in the city would be required to meet tough environmental guidelines, making San Francisco "the greenest large city in the United States of America," Newsom said.

"I will sign it, fast track it," the mayor said Wednesday. "As far as I'm concerned, if you want to do business in San Francisco ... these are going to be the minimum requirements. Anyone who's got to process a permit should be on notice."

The ordinance would require that new residential buildings over 75 feet tall, new commercial buildings over 5,000 square feet and renovations on buildings over 25,000 square feet comply with stringent standards developed by the U.S. Green Building Council.

By 2012, new projects and renovations would be required to comply with the strictest levels of those standards known as Leadership in Energy and Environmental Design, or LEED. Last year, the city began fast-tracking permits for developers who voluntarily met the LEED standards.

"In some respects, buildings are our legacy. They're our heritage," said Phil Williams, vice president of Webcor Builders, one of the city's largest private builders, and chairman of the city task force that earlier this year recommended the new building requirements. "Buildings last 50, 75, 100, 150 years, and they don't get better once they're done. We thought it was extremely important for us to make an impact now, not just for our own lives but (for) the next generation of San Franciscans."

The new standards, if implemented, would affect new buildings subject to permit approval beginning next year.

Newly constructed city government buildings already are required to meet the green standards, which include using natural lighting, solar power, low-flow water fixtures and nontoxic paints.

City officials estimate the new rules could reduce carbon dioxide emissions in the city by 60,000 tons and save 220,000 megawatt hours of power by 2012.

"If you're going to get serious about the environment ...we have to get serious about the operation of these buildings and the construction and the design elements," Newsom said.

E-mail Cecilia M. Vega at cvega@sfchronicle.com.

This article appeared on page B - 3 of the San Francisco Chronicle