Reacting to plummeting oil prices, Southern California Gas Co. asked the Public Utilities Commission to let it lower the price that it charges electric utilities for gas to fuel their power plants. Unless that rate is cut, the company warned, the electric utilities--among its largest customers--will switch to lower-priced oil to generate power. The proposed cut would drop the current rate of $2.80 per million British thermal units to $2.25 for the 30 days beginning March 14. After a similar request last month, the PUC approved the $2.80 rate. Utilities account for about 20% of gas company sales, but they are required to buy the least expensive fuel available--even though gas is environmentally cleaner.