* Japan PM says final decision after local authorities make up minds
* Restart of Kansai Electric's two reactors risks public backlash
* Reactor restart would ease concerns about power shortages (Adds PM comments)
By Kentaro Hamada and Linda Sieg
TOKYO, May 30 (Reuters) - Japanese Prime Minister Yoshihiko Noda, keen to restart idled nuclear reactors to avoid a summer power crunch, said on Wednesday it was necessary to start those whose safety has been confirmed, adding he was winning understanding from local authorities.
Nuclear power supplied nearly 30 percent of Japan's electricity needs before last year's earthquake and tsunami cripped the Fukushima plant - the world's worst nuclear accident in 25 years. But all of the country's 50 reactors have since been taken offline for checks.
The government has been struggling to win support from local authorities for the restarts, although their permission is not legally required.
Noda, talking after a meeting with key ministers to discuss resuming operations at two of Kansai Electric Power Co's reactors in western Japan, said he would make a final decision once local authorities have made up their minds.
A group of regional governors, long concerned about whether it was safe to resume power generation at Kansai Electric's No. 3 and No. 4 reactors in Ohi, western Japan, signalled their agreement to the restarts as a "limited" step.
The governor of the host prefecture of Fukui and the mayor of the town of Ohi where the reactors are located have yet to give final approval, although Ohi's local assembly has signed off on resuming operations.
"If we get a decision by local authorities, then we will discuss among the four key ministers and I will make the final decision," Noda told reporters.
A decision by Noda and key ministers to restart the reactors would ease worries about power shortages among firms in the region, including struggling electronics giants Panasonic Corp and Sharp Corp. But the move could also irk voters and undermine Noda's already sagging public support.
Noting the central government has yet to set up a new regulatory agency, promised after the disaster, the Union of Kansai Governments said current safety standards were therefore provisional. Parliament began debate on creating the new agency this week after months of delay.
Anti-nuclear activists have cast doubt on the government's assurances that the two reactors at Kansai Electric Power Co's Ohi plant in Fukui, western Japan, are safe.
"We have consistently said that none of the safety or emergency measures that have been called for by experts in the community has been completed," said Greg McNevin, a spokesman for Greenpeace International.
"Our consistent position is that this is being rushed."
Kansai Electric has said it would take six weeks to reconnect them to the grid and the government has asked businesses and consumers in its service area to cut summer electricity useage by 15 percent from 2010 levels.
Reporting by Kentaro Hamada; Writing by Linda Sieg; Editing by Edmund Klamann and Nick Macfie