With California regulators poised today to set in stone the state’s zero-emission vehicle (ZEV) mandate, automakers have been mounting a last-ditch effort to prevent the rule from being so tough. The rule would require that thousands of ZEVS be sold in the state by 2003. Among their complaints, automakers are contending that the electricity used by electric cars would bring California’s already-strapped energy system to its knees. The state Energy Commission disagrees, saying that the electricity needed to power the cars would be trivial relative to the state’s supply and that most cars would be recharged at night, when electricity demand is at its lowest.