California regulators cut by 70 percent the number of emission-free vehicles that automobile manufacturers must sell in California in the three years beginning in 2012. At the same time, the regulators effectively required, for the first time, that tens of thousands of plug-in hybrid vehicles be sold in those years. A prototype all-electric Tesla roadster shown in California in February 2007. Tesla's vice president, Darryl Siry, says the car will accelerate from zero to 60 miles an hour in four seconds. The cutback in the requirement for either all-electric or fuel-cell vehicles dismayed some environmentalists. But their pleasure at the likelihood that the decision will mean a new infusion of research dollars in plug-in hybrid technology, which is still more of a curiosity than a market force, largely made up for it. The unanimous vote on Thursday by the California Air Resources Board to change its mandate for what it calls zero-emission vehicles did not take the cutback as far as its staff members had recommended. Earlier this year, they had called for a 90 percent cut in the requirements that were originally set in the early 1990s. The board estimated that the new mandates would cost auto manufacturers more than $1 billion annually for those three years. David Barthmuss, a representative of General Motors, said after the vote that those in attendance "are still scratching our heads' to understand the full implications of the new mandates. But he said that two cars on the company's drawing boards, the Chevrolet Volt and the Saturn Vue, would probably be sold in large numbers in California as a result of the vote. The Volt, which uses some gasoline, but only to power its battery, not to turn its wheels, could be counted as part of GM's obligation under the mandate, he said, as would the Saturn Vue, a plug-in hybrid. But, Mr. Barthmuss said, the mandate "still requires infrastructure,' saying that there are only a few