TOKYO — Japanese inspectors found the first case of radioactive contamination in rice, the national grain, on Friday, adding it to the list of foods harmed by the accident at the stricken Fukushima Daiichi nuclear plant.

Inspectors in Ibaraki Prefecture, just north of Tokyo, found radioactive cesium in a sample of rice from the city of Hokota, about 100 miles south of the radiation-spewing nuclear plant. The prefecture said the radiation was well within safe levels: it measured 52 becquerels per kilogram, about one-tenth of the government-set limit for grains.

The prefecture said two other samples tested at the same time showed no contamination.

The Agriculture Ministry said it was the first time that more than trace levels of cesium had been found in rice, though it said there was no health risk. Still, the discovery won wide attention here. Rice is a staple in most Japanese dishes and holds a place in the collective national heart that exceeds that of apple pie for Americans or baguettes for the French.

Fears of atomic contamination of the rice crop had been building ahead of this year’s autumn harvest, the first since the earthquake, tsunami and nuclear accident in March. Adding to the anxiety is that Japan’s mountainous northeast, which bore the brunt of the triple disaster, is one of the nation’s most productive rice-growing regions.