As the traditional Labor Day kickoff to the fall election campaign approaches, the battle is intensifying over Proposition 23, the California ballot initiative that would effectively repeal the state’s landmark climate change law.

And thus the title of a gathering Tuesday at Google’s Silicon Valley headquarters: “Electric Bills & Oil Spills: Will California Continue to be a Clean Energy Leader?”

The not-so-subtle subtext: Not if Prop 23 passes.

“We’re strongly behind the No on 23 campaign,” Bill Weihl, Google’s green energy czar (yes, that’s his title), said as he kicked off the event in a company café packed with Bay Area green A-listers.

Not surprisingly, the panel focused less on the environmental consequences of Prop 23 than on the potential for the ballot initiative to derail California’s green tech revolution.

“Proposition 23 will kill markets and the single largest source of job growth in California in the last two years,” declared Vinod Khosla, a leading green tech investor, referring to the clean energy economy. “Not only that, it’ll kill investment in the long term for creating the next 10 Googles.”

Chipped in Weihl: “For California, we can either lead in this and invest in it and participate in this huge growth sector or cede that to China, India, and other places. It would be crazy for us to sit back and let others take that opportunity.”

Underwritten by Texas oil companies Tesoro and Valero and other out-of-state fossil fuel corporations, Prop 23 would suspend California’s global warming law — popularly known as AB 32, as in Assembly Bill 32 — until the unemployment rate drops to 5.5 percent for four consecutive quarters. (In other words, never.) AB 32 requires California to reduce greenhouse gas emissions to 1990 levels by 2020, which most likely would be accomplished through a cap-and-trade market.

Khosla and Weihl were joined on a panel by Mary Nichols, head of the California Air Resources Board, the agency charged with implementing AB 32; and Tom Bottorff, an executive with the utility PG&E.

“If you listen to the arguments of the proponents of Prop 23, their vision of California is a World War II or 1950s vision,” said Nichols, who before her appointment by Gov. Arnold Schwarzenegger was a longtime activist with the Natural Resources Defense Council. “They want to go back to a time when rubber factories and building of aircraft and automobiles were the main businesses of California.”

As the fight over Prop 23 heats up, expect to see a lot more of such talk from a place where the future is the main export.