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Most are pressing local officials to test radiation levels in school lunches and provide more detailed checks of school grounds, but Mrs. Itoh and others also have lobbied senior government officials. Mothers make up the bulk of the membership, but fathers are getting involved, too.

“We’re still small, but some of the mothers involved didn’t even go to vote. It’s these mothers who are submitting petitions and making calls and gathering signatures,” Mrs. Itoh said. “I believe this will be a factor in changing the direction of our country.”

She said the Internet has been invaluable in connecting parents, partly because Japan has few forums for citizens to exchange ideas. The crisis has changed perceptions of the Internet among mothers, many who previously considered it a dubious source of information.

Separately, individuals and loosely formed community groups are going around their neighborhoods checking radiation levels or sending soil samples to laboratories for testing.

The Radiation Defense Project, which grew out of a blog and then a Facebook page, says its testing has revealed several “hot spots” in Tokyo with trace amounts of radioactive cesium it believes came from Fukushima, said group founder Kouta Kinoshita, a former TV journalist.

Another group is collecting signatures for a petition to hold a referendum in Osaka and Tokyo on whether Japan should use nuclear power. The vote would not be legally binding, but it could send a message to policymakers.

The government’s management of the nuclear crisis did little to instill confidence that it will be able to tackle looming problems, including a rapidly aging population and a public debt that is twice the nation’s gross domestic product. Both problems will burden the younger generation.

Still, the growing dissatisfaction may not be enough to bring about fundamental change.

Japan’s affluence is an obstacle. Most people live comfortably and are reluctant to make too big a fuss, even if they are unhappy with the political leadership. Culturally, it is considered better to adjust to one’s surroundings than to try to change them, said Ken Matsuda, a sociologist at Kansai Gaidai University in Osaka.

“Most people aren’t hungry or angry,” he said. “People need a clear enemy, and there’s no clear enemy in Japan. Public anger needs to hit a critical mass. It’s not anywhere near that.”

Some Japanese wonder if the stoicism and perseverance that were widely praised in the aftermath of the tsunami could also be a liability.

“The disasters didn’t stimulate a real sense of urgency,” said Ichiro Asahina, who quit his job as a bureaucrat in the economic ministry last year after 14 years to establish a think tank and leadership institute in Tokyo.

“To stimulate change,” he added, “we may need to confront even more severe crises.”