TOKYO — As Japan edged forward in its battle to contain the damage at its ravaged nuclear power plants on Saturday, the government said it had found higher than normal levels of radioactivity in spinach and milk at farms up to 90 miles away from the plants, the first confirmation that the unfolding nuclear crisis has affected the nation’s food supply.

While officials played down the immediate risks to consumers, the findings further unsettled a nation worried about the long-term effects of the hobbled reactors.

The Tokyo Electric Power Company, with help from the Japan Self-Defense Forces, police officers and firefighters, continued efforts to cool the damaged reactors on Saturday to try to stave off a full-scale fuel meltdown and contain the fallout. The latest plan involved running a mile-long electrical transmission line to Reactor No. 2 at the Fukushima Daiichi Nuclear Power Station to try to restore power to its cooling system.

About 500 workers from the utility connected the power line on Saturday. They were checking the cooling system, which has been disabled since the earthquake and tsunami hit more than a week ago, and hoped to restart it on Sunday.