TOKYO (REUTERS) - A Japanese court on Wednesday ruled against restarting a nuclear power plant in a rare victory for anti-nuclear activists after the Fukushima disaster, and dealing a blow to government efforts to end a nationwide nuclear freeze.

The ruling against the restart of a western power station run by Kansai Electric Power Co was a scathing critique of the Japanese nuclear industry's risk management, but does not block a restart under Japanese law as it is not a final ruling.

The utility, the country's second-largest, which supplies electricity to a key manufacturing region, said it would appeal the ruling against restarting reactors 3 and 4 at the Ohi nuclear plant in Fukui prefecture, 500 km west of Tokyo.

All 48 of Japan's nuclear reactors have been idled for safety checks after an earthquake and tsunami triggered triple meltdowns at Tokyo Electric Power Co's Fukushima Daiichi plant, forcing more than 150,000 residents to evacuate. Japan faces the unprecedented task of decommissioning all three of the destroyed reactors in the coming decades.

"Atomic power is important to society but it is a means to produce electricity and it is subordinate to the fundamental cornerstone of personal rights," the three Fukui District Court judges wrote in their ruling.

The court rejected Kansai Electric's safety guarantees as insufficient in addressing the seismological risk. "From the perspective of protecting personal rights and health from radioactive substances, this leaves doubts about whether safety technology and equipment will be sufficient.

"To the contrary, it forces us to admit that this is a fragile notion without a firm basis, predicated on an optimistic outlook."

Kansai Electric called the ruling "regrettable".

While the district court decision does not legally block the restart of the reactors, bringing them back online in the face of such a judicial verdict could open the regulator and the government to criticism.

The Japanese public is sceptical of nuclear power, which provided about 30 per cent of the electricity used by the world's third-biggest economy before the Fukushima disaster.

Opposition to restarts runs about two-to-one in recent polls, while a March survey in the Asahi newspaper found that 80 per cent favoured a gradual exit from atomic power.

"This is a landmark ruling, one that gives voice to many residents who live near nuclear plants, who have previously had no voice," said city councilwoman Harumi Kondaiji of Tsuruga City in Fukui prefecture, 60 km from the Ohi plant.

Yet anti-nuclear forces have failed to turn sentiment into political clout against the pro-nuclear government of Prime Minister Shinzo Abe, who has vowed to restart plants that pass the tougher, post-Fukushima safety checks.

A Reuters analysis in April indicated the Ohi reactors were among the most likely to be restarted.

Wednesday's ruling complicates the restart of other reactors, with the safety checks bogged down by paperwork and disputes over interpreting new guidelines.

Chief Cabinet Secretary Yoshihide Suga reaffirmed the government's plan to restart reactors that pass regulatory checks. Japan's top nuclear regulator told reporters it would continue vetting the Ohi plants, but declined to comment on the ruling.

But nuclear opponent Aileen Mioko Smith, of the group Green Action, said the rare victory came "right in the middle of the restart process...It could have very well have repercussions."

An Osaka court this month rejected a suit against the Ohi reactors in which Smith's group was a plaintiff.