U.N. nuclear experts have endorsed stress tests designed to show that Japanese nuclear plants could withstand a repeat of last year's quake and tsunami, as the government campaigns to restart idled reactors and avoid a summer power crunch.

The government, though, still faces an uphill battle to restore public trust in the nation's power utilities after the March 11 disaster wrecked the Fukushima nuclear power plant, triggering the world's worst nuclear crisis in 25 years.

The Vienna-based International Atomic Agency's (IAEA) team has been in Japan at the request of the government to review stress tests conducted by its Nuclear and Industrial Safety Agency (NISA) on halted nuclear reactors to verify their safety.

We concluded that NISA's instructions to power plants and its review process for the comprehensive safety assessments are generally consistent with IAEA safety standards, James Lyons, the leader of the 10-member IAEA team, said on Tuesday.

We were very impressed with the way Japan quickly implemented the emergency safety measures after the accident in March. They have also been very active in participating in the international community to determine the steps forward, Lyons added to reporters.

He also pointed out areas that Japan could improve upon, such as communicating with local communities about stress tests.

NISA had done a good job in the transparency of information on their website, but we feel that it is also important for them to hold meetings in the vicinities of nuclear power plants to discuss their findings with the local population, Lyons said.

Stress tests are computer simulations that evaluate a nuclear reactor's resilience to severe shocks.

NISA completed a review of the stress tests earlier in January and said they showed reactors at Fukui prefecture's Ohi plant, the first to be assessed, were capable of withstanding an impact similar to the magnitude 9.0 earthquake and massive tsunami that wrecked the Fukushima plant.

Some experts, however, have questioned the validity of the stress tests, charging the IAEA's visit was just for show.

It is obvious that a visit by an international organisation advocating nuclear power is part of a political agenda that is built into a story already finished in advance, said University of Tokyo professor Hiromitsu Ino and former nuclear plant design engineer Masashi Goto in a joint statement last week.

Ino and Goto, who serve on a committee that advises on NISA's review of the stress tests, said the tests were insufficient as they only simulate one natural disaster at a time and do not take into account the possibility of the sort of equipment failure and human error seen at Fukushima.

Others suggested the IAEA's stamp of approval would not be enough to alleviate public concern.

The public mistrust towards the government's handling of information over the nuclear accident is high and I don't think the review will change that, said Atsuo Ito, a political analyst.

ENERGY POLICY SHIFT

In another effort to restore public confidence in nuclear power, the cabinet on Tuesday approved bills that would set up a new nuclear safety agency, separating regulation of the industry from the trade and industry ministry, which has promoted nuclear power and came under criticism for its cosy ties with utilities.

The Fukushima disaster has also prompted a major shift in Japan's energy policy.

The resource-poor nation had aimed to increase the share of nuclear power from a third to more than half of the power supply by 2030 before the disaster, but it now looks to reduce its reliance on nuclear power and raise the role of renewable sources such as wind and solar power.

But with only three of the country's 54 nuclear reactors running, and public anxiety preventing the rest from being restarted after routine checks, the government wants to avoid a an economically crippling power crunch in the summer and hopes the stress tests will help persuade a wary public that it is safe to restart some of the reactors.

Local governments hosting nuclear plants, however, have said the stress tests were not sufficient to allow them to give their approval, with some requesting that findings from the Fukushima disaster be considered in drafting new safety standards as well.

A utility would not be violating any law if it went ahead and restarted a reactor after properly completing scheduled maintenance. But the Fukushima accident has heightened public concern over nuclear safety, making local consent an important part of the restart process, a trade ministry official said.

Japan had promoted nuclear power as safe, cheap and clean before the Fukushima crisis.

The myth that nuclear power was absolutely safe is a theme we will explore. We need to find out how such a mindset developed, Kiyoshi Kurokawa, head of a parliamentary committee investigating causes of the Fukushima accident, told reporters on Monday.

(Additional reporting by Kiyoshi Takenaka; Editing by Linda Sieg and Tomasz Janowski)