Mr. Hosono, the minister charged with dealing with the nuclear crisis, has said that certain information, including the Speedi data, had been withheld for fear of “creating a panic.” In an interview, Mr. Hosono — who now holds nearly daily news conferences with Tepco officials and nuclear regulators — said that the government had “changed its thinking” and was trying to release information as fast as possible.

Critics, as well as the increasingly skeptical public, seem unconvinced. They compare the response to the Minamata case in the 1950s, a national scandal in which bureaucrats and industry officials colluded to protect economic growth by hiding the fact that a chemical factory was releasing mercury into Minamata Bay in western Japan. The mercury led to neurological illnesses in thousands of people living in the region and was captured in wrenching photographs of stricken victims.

“If they wanted to protect people, they had to release information immediately,” said Reiko Seki, a sociologist at Rikkyo University in Tokyo and an expert on the cover-up of the Minamata case. “Despite the experience with Minamata, they didn’t release Speedi.”

In Koriyama, a city about 40 miles west of the nuclear plant, a group of parents said they had stopped believing in government reassurances and recently did something unthinkable in a conservative, rural area: they sued. Though their suit seeks to force Koriyama to relocate their children to a safer area, their real aim is to challenge the nation’s handling of evacuations and the public health crisis.

After the nuclear disaster, the government raised the legal exposure limit to radiation from one to 20 millisieverts a year for people, including children — effectively allowing them to continue living in communities from which they would have been barred under the old standard. The limit was later scaled back to one millisievert per year, but applied only to children while they were inside school buildings.

The plaintiffs’ lawyer, Toshio Yanagihara, said the authorities were withholding information to deflect attention from the nuclear accident’s health consequences, which will become clear only years later.

“Because the effects don’t emerge immediately, they can claim later on that cigarettes or coffee caused the cancer,” he said.

The Japanese government is considering monitoring the long-term health of Fukushima residents and taking appropriate measures in the future, said Yasuhiro Sonoda, a lawmaker and parliamentary secretary of the Cabinet Office. The mayor of Koriyama, Masao Hara, said he did not believe that the government’s radiation standards were unsafe. He said it was “unrealistic” to evacuate the city’s 33,000 elementary and junior high school students.

But Koriyama went further than the government’s mandates, removing the surface soil from its schools before national directives and imposing tougher inspection standards than those set by the country’s education officials.

“The Japanese people, after all, have a high level of knowledge,” the mayor said, “so I think information should be disclosed correctly and quickly so that the people can make judgments, especially the people here in Fukushima.”