TOKYO — Japan’s embattled prime minister, Naoto Kan, defended his government’s handling of the nation’s nuclear crisis on Saturday, a day after an adviser resigned during a tearful news conference in which he charged that the government was not adequately protecting the population from radiation.

In one of his most damaging charges, the adviser, Toshiso Kosako, drew attention to a recent government decision to allow children living near the crippled Fukushima Daiichi nuclear plant to receive doses of radiation equal to the international standard for nuclear power plant workers. That level is far higher than international standards set for the public. “I cannot allow this as a scholar,” said Mr. Kosako, an expert on radiation safety at the University of Tokyo.

He also blasted the government for what he said was a lack of transparency in releasing radiation levels around the Fukushima Daiichi plant, and for setting an overly high limit on radiation exposure for workers who have spent weeks struggling to keep the plant under control.

Government advisory positions are considered prestigious, and it is highly unusual for an academic to quit one in protest. The prime minister brought Mr. Kosako on as an adviser after the powerful March 11 earthquake and tsunami damaged the plant, causing the world’s biggest nuclear disaster since the Chernobyl accident in 1986.