By Risa Maeda
TOKYO (Reuters) - Japan's nuclear watchdog on Wednesday postponed the completion of its review on stress tests on the first pair of dozens of idled reactors, an initial step in rebuilding public trust in atomic energy after the worst nuclear accident in 25 years.
Only three of Japan's 54 reactors are online 11 months after a major earthquake and tsunami crippled the Fukushima Daiichi nuclear power plant. Many have been stopped for regular maintenance, during which utilities are conducting stress tests.
The accident, the most serious since the explosion and fire at Chernobyl in Ukraine in 1986, led to widespread contamination, prompted mass evacuations, caused upheaval throughout the nuclear industry and forced the government to review its overall energy policy.
Clearing the stress tests against extreme events -- like the March 11 disaster -- is a necessary hurdle to clear for the restart of the two reactors run by the Kansai Electric Power Co. at the Ohi plant in western Japan.
The Nuclear and Industrial Safety Agency (NISA) set no date for the review to be completed.
"We will do our homework after today's hearing, discuss by ourselves and decide on it when appropriate," Tomoya Ichimura, director of NISA's nuclear safety regulatory standard division, told reporters after a meeting of a panel of experts.
Some improvements had already been introduced at the two 1,180 megawatt reactors after computer-simulated test results suggested some equipment and other factors needed improvement.
The timing of the watchdog's first such stress test approval is being carefully watched. Industry and government officials are keen to see some reactors brought back on stream soon to avoid a potentially serious power crunch in the summer.
Once the tests are completed, they must be validated by the Nuclear Safety Commission of Japan and approved by four cabinet ministers, including Trade Minister Yukio Edano and Prime Minister Yoshihiko Noda.
Approval must then be forthcoming from local authorities hosting nuclear power plants. Although agreement is not required by law, ministers are mindful of public concerns about safety.
Trade minister Edano, who holds the energy portfolio, said this week he had not set deadlines to resume operations at nuclear reactors after a media report said the government aimed to restart the two Ohi reactors around April.
Ichimura on Wednesday declined to say when NISA will compile its final report or if the panel of experts will talk about the Ohi reactors again when they next meet on February 20.
A new atomic safety regulator under the auspices of the environment ministry is set to replace NISA in April in a move to separate the regulatory role from the trade ministry, which also promotes nuclear.
The government has submitted to parliament a revision of laws regulating nuclear plant operators.
(Reporting by Risa Maeda; Editing by Ron Popeski)