* Most of North America has enough power for summer * Texas demand is rising faster than power resources * California power supply tight until San Onofre back May 30 (Reuters) - Most of North America has enough power to meet peak air conditioning demand this summer, but problems could arise in Texas and California, the North American Electric Reliability Corp (NERC) said Wednesday in its summer assessment. NERC is responsible for the reliability of the power grid in the United States, Canada and parts of Mexico. The Electric Reliability Council of Texas (ERCOT), which oversees the power grid for most of Lone Star State, projected reserve margins would be below targets, NERC said. Power companies use reserves to help keep the lights on in case demand is stronger than forecast or plants or transmission lines unexpectedly shut. "With continued growth in peak demand and only a small amount of new generation coming online, resource adequacy levels in ERCOT have fallen below targets," John Moura, manager of Reliability Assessment at NERC, said in a release. "If ERCOT experiences stressed system conditions or record-breaking electricity demand due to extreme and prolonged high temperatures, system operators will most likely rely on demand response and emergency operating procedures," Moura said. He said those procedures may include rotating outages to maintain the reliability of the interconnection. In California, NERC projected reserves could be tight, but manageable, especially in the southern part of the state if the San Onofre nuclear power plant remains offline this summer. The two reactors at the 2,150-megawatt (MW) San Onofre nuclear plant shut in January and remain out of service due to problems with the steam generators. Southern California Edison (SCE), a unit of California power company Edison International, operates the plant for its owners SCE, Sempra Energy's San Diego Gas & Electric and the City of Riverside. SCE cannot say when San Onofre will return to service. California's power grid operator started preparing for the possibility of a summer without the nuclear plant a few months ago. In addition, NERC said Massachusetts could have a problem in the Boston area if some power plants there receive less liquefied natural gas (LNG) supplies than needed to run. That possibility may require the region's grid operator, ISO New England, to implement some proactive measures to keep the system reliable, NERC said. DEMAND DOWN FOR MOST NERC forecast total peak demand would be about 3,700 MW lower in the summer of 2012 compared with the same period in 2011. But peak demand in ERCOT was expected to rise 1.7 percent, the largest increase in North America. NERC said capacity resources have grown across North America by about 12,310 MW, especially in the Southeast and Northeast regions.