TOKYO (AP) ― Criticism of the Japanese government’s handling of the crisis at a radiation-spewing nuclear power plant increased Saturday, with a new poll indicating three-quarters of the people disapprove and a key adviser quitting in protest.

A Kyodo News service poll released Saturday showed that Prime Minister Naoto Kan’s support ratings were plunging.

The poll reported that 76 percent of the respondents think Kan is not exercising sufficient leadership in handling the country’s earthquake, tsunami and nuclear triple crisis, up from 63.7 percent in the previous survey in late March.

It also showed 23.6 percent of respondents think Kan should resign immediately, up from 13.8 percent in the previous survey.

The nationwide telephone survey of 1,010 people eligible to vote was conducted Friday and Saturday. No margin of error was provided.

Toshiso Kosako, a professor at the University of Tokyo’s graduate school and an expert on radiation exposure, announced late Friday that he was stepping down as a government adviser over what he lambasted as unsafe, slipshod measures.

Kan appointed Kosako after the magnitude-9.0 earthquake and tsunami struck northeastern Japan on March 11. The disaster left 26,000 people dead or missing and damaged several reactors at the Fukushima Daiichi nuclear power plant, setting off the world’s worst nuclear crisis since Chernobyl in 1986.

In a tearful news conference, Kosako said he could not stay and allow the government to set what he called improper radiation limits of 20 millisieverts a year for elementary schools in areas near the plant.

“I cannot allow this as a scholar,” he said. “I feel the government response has been merely to bide time.”

Kosako also criticized the government as lacking in transparency in disclosing radiation levels around the plant, and as improperly raising the limit for radiation exposure for workers at Fukushima Dai-ichi, Kyodo reported.

The prime minister defended the government’s response as proper.

“We welcome different views among our advisers,” Kan told parliament Saturday in response to an opposition legislator’s questions.

A government advisory position is highly respected in Japan, and it is extremely rare for an academic to resign to protest government policy.

The science and education ministry has repeatedly defended the 20-millisievert limit for radiation exposure as safe, saying that efforts are under way to bring the limit down to 1 millisievert. Some people have expressed concerns, noting that children are more vulnerable to radiation than adults.

Workers in the U.S. nuclear industry are allowed an upper limit of 50 millisieverts per year. A typical individual might absorb 6 millisieverts a year from natural and man-made sources such as X-rays.

Radiation specialists say cumulative doses of 500 millisieverts raise cancer risks. Evidence is less clear on smaller amounts, but in theory, any increased radiation exposure raises the risk of cancer.

Japan, which has 54 nuclear reactors, has long been a major proponent of atomic power, constantly billing its technology as top-rate and super-safe. Japan’s government has also been trying to make deals to build nuclear power plants in other countries, although such attempts are likely to fall flat after the Fukushima Dai-ichi accident.

As the only country in the world to suffer atomic bombings, as it did at Hiroshima and Nagasaki during World War II, Japan has long had a powerful anti-nuclear movement, and such protests have become louder recently.

About 1,000 protesters gathered Saturday in Tokyo’s Yoyogi Park, beating drums, shouting “No more nukes” and holding banners that read “Electricity in Tokyo, sacrifice in Fukushima.”

“We knew all along nuclear power was dangerous. I just didn’t know how to express myself,” said one of the protesters, 50-year-old Yoshiko Nakamura, who was taking part in her second demonstration in two weeks. “This is a great opportunity to send a message and voice my fears.”

Tokyo Electric Power Co., the utility that runs Fukushima Daiichi, said Saturday that the radiation exposures for two workers, upon more careful recalculation, was found to have reached near the crisis-time limit of 250 millisieverts.

Usually, TEPCO plant workers are limited to 100 millisieverts of radiation exposure over five years, with no year exceeding 50 millisieverts. That was raised to 250 millisieverts, with government approval, because of the crisis.

One worker was measured at 240.8 millisieverts, while another at 226.6 millisieverts. Both workers were temporarily hospitalized last month after being exposed to highly radioactive water that had leaked into the reactor turbine room.

Last week, TEPCO said one female worker at Fukushima Daiichi was exposed to radiation three times the legal limit, at 17.55 millisieverts. Exposure for women is limited to 5 millisieverts over 3 months because of pregnancy concerns.

TEPCO spokesman Junichi Matsumoto said the company had been preoccupied with monitoring radiation for male workers, and forgot that women’s limits were far lower.

“We are extremely sorry,” he told reporters last week.

Also on Saturday, parliament’s lower house approved a special 4 trillion yen ($50 billion) budget to help finance post-tsunami rebuilding efforts, in what officials say will likely be the first installment of reconstruction funding.

The budget now goes to the less powerful upper house, where opposition is unlikely, and the budget is expected to win passage early next week.