SAN ONOFRE STATE BEACH, Calif. — More than seven million people live within 50 miles of the San Onofre Nuclear Generating Station, which is about halfway between Los Angeles and San Diego. But for decades, residents here largely accepted, if not exactly embraced, the hulking nuclear plant perched on the cliffs above this popular surfing beach as a necessary part of keeping the lights on in a state that uses more electricity than all of Argentina.

“I don’t think about it too much,” said David Vichules, 55, who has been surfing here since before the plant opened in 1968. “I guess it’s risk and benefit.”

All that changed, however, after the Fukushima Daiichi meltdown in Japan last year, followed in January by a small leak of radioactive steam here caused by the deterioration of steam tubes that had been damaged by vibration and friction. The twin generators at the San Onofre plant have been off-line for five months, and the plant has subsequently become a point of contention in the fight over nuclear power in the United States.

The leak has galvanized opposition to the nuclear plant among local residents, who are calling for San Onofre to remain shuttered for good.