The Energy Department will propose new energy-efficiency standards for central air conditioning today in an effort to prevent power outages on hot days when everyone cranks up the cooling.

The proposal--which could increase efficiency by as much as 30 percent--comes at a time when the nation's power grid has been put under increasing strain, with energy consumption increasing faster than the nation's ability to transmit power.

This year, utilities including Potomac Electric Power Co. hit new records for peak demand during summer heat waves, and many areas, including New York, Chicago and New Orleans, experienced power outages.

The heaviest strain on the nation's power-transmission systems typically come in the summer, when air conditioning can account for more than half of household electricity consumption, according to Energy Secretary Bill Richardson. "By increasing the efficiency of central air conditioning, we will help minimize the impact of future heat waves on the power grid and help consumers and business save money and energy," he said.

During periods of normal demand, utility companies use their lower-cost equipment to provide electricity. When demand peaks, the companies use everything--including smaller, higher-cost generating equipment. That puts a strain both on the system's generating power and on the transmission systems that carry the energy into sweltering homes.

The Energy Department had been planning to propose new standards for air conditioning, but after this summer's strain on the system Richardson accelerated the schedule. The proposals to be published today in the Federal Register are designed to take effect by December of next year.

The department is asking for comments and calling on the industry, energy-efficiency advocates and environmentalists to collaborate on a final proposal. Energy standards for central air conditioning are measured by something called the Seasonal Energy Efficiency Rating, or SEER. The current minimum standard is 10, with the equipment in use averaging slightly higher efficiency.

The department's proposal suggests a new standard that could range from 11 to 13 SEER.

In recent years, utilities have been reluctant to spend more on expanding their ability to produce or transmit power because of uncertainty over the future shape of the industry. Still a heavily regulated system of regional monopolies, the electric power industry is expected to be transformed into a system of larger companies that will vie to produce, market and transmit power in a competitive national market.

"What is clear regarding power outages is that we've got to improve the reliability of the electricity supply and cut peak demand," said Dan Reicher, assistant secretary for energy efficiency and renewable energy. "The most important way to cut peak demand is to cut air-conditioning load."