By Kentaro Hamada

NIIGATA, Japan (Reuters) - A regional election north of Tokyo between candidates most Japanese have never heard of may decide the fate of the world's biggest nuclear plant and mark a turning point for an industry all but shut down after the Fukushima disaster.

The campaign for governor of Niigata Prefecture has boiled down to two men and one issue: whether to restart the seven-reactor Kashiwazaki-Kariwa Nuclear Power Station.

Reviving the seven-reactor giant, with capacity of 8 gigawatts, is key to saving Tokyo Electric Power, which was brought low by the 2011 Fukushima explosions and meltdowns, and then the repeated admissions of cover-ups and safety lapses after the world's worst nuclear disaster since Chernobyl in 1986.

Tepco, as the company supplying about a third of Japan's electricity is known, is in turn vital to Prime Minister Shinzo Abe's energy policy, which relies on rebooting more of the reactors that once met about 30 percent of the nation's needs.

But Ryuichi Yoneyama, 49, an anti-nuclear doctor-lawyer who has never held office and is backed by mostly left-wing parties, has made a tight race for governor of Niigata against an initially favored veteran politician from Prime Minister Shinzo Abe's pro-nuclear party, Japanese media say.

In a sign that Abe's Liberal Democratic Party also sees a tough contest, party heavyweights were dispatched to campaign for Tamio Mori, 67. The former mayor and construction ministry bureaucrat is seen more likely to allow Kashiwazaki-Kariwa to restart.

Distrust of Tepco, put under government control in 2012, is so high in Niigata that this election has become a litmus test for nuclear safety and put Abe's energy policy and Tepco's handling of Fukushima back under the spotlight.

The government wants to restart units that pass safety checks, also promoting renewables and burning more coal and natural gas.

RADIATION LEAKS

Only two of Japan's 42 reactors are running more than five years after Fukushima, but the Niigata plant's troubles go back further.

Several reactors at Kashiwazaki-Kariwa have been out of action since an earthquake in 2007 caused radiation leaks and fires in a disaster that prefigured the Fukushima calamity and Tepco's bungled response.

A Tepco spokeswoman said the company could not comment on the election and was committed to boosting safety at the plant.

On the campaign trail in Niigata, help for Tepco is in short supply.

Yoneyama has promised to continue the outgoing governor's policy of refusing to allow a restart unless Tepco provides a fuller explanation of the Fukushima disaster.

He has run for local office unsuccessfully four times but says this time he feels different, as the public supports his anti-nuclear, anti-Tepco message.

Yoneyama, who has worked as a radiological researcher, says Tepco doesn't have the means to prevent Niigata children from getting thyroid cancer in a nuclear accident, as he says has happened in Fukushima. And he says the company doesn't have a solid evacuation plan.

"As I go from town to town and village to village, I hear the same thing: 'We want you to protect this town. We want you to protect our hometown, our lives and our children's future,'" he told a crowd in Nagaoka this week.

The LDP's Mori has toned down his support for restarting the plant as the race tightens, media say, and now insists that safety is the top priority for Kashiwazaki-Kariwa, while promoting the use of natural gas and solar power in Niigata.

LDP heavyweight Shigeru Ishiba, a former cabinet minister and party secretary-general, told Reuters the party sent him to Niigata to campaign for Mori because "we can't take anything for granted".

"Mr. Mori is not a person who just acquiesces to what the national government says," Ishiba said. "He has courage and will stand up to the government if he thinks our policies are wrong."

(Additonal reporting by Osamu Tsukimori; Writing by Aaron Sheldrick; Editing by William Mallard and Nick Macfie)