The current cold snap has caused natural gas usage in San Diego County to reach record levels, leading San Diego Gas & Electric officials to warn their customers of massive heating bills unless precautionary steps are taken. Last Friday an hourly record of 22 million cubic feet of natural gas was used between 7 a.m. and 8 a.m., according to Karen Duncan, a spokeswoman for SDG&E. A 24-hour record also was nearly broken last Thursday and Saturday as gas and electric customers used 444 million cubic feet of natural gas on each day, Duncan said. The 24-hour record of 445 million cubic feet was set Feb. 4, 1985, Duncan said. Officials from SDG&E, already beset by 200 calls a day from customers complaining about last month's bills, forsee more calls next month unless steps are taken. They suggest that customers wear warm clothing indoors and turn down their thermostats.