TOKYO, Feb 13(Reuters) - Japan's nuclear power advocates have pulled out all the stops since the Fukushima crisis, even arguing that the only nation to suffer an atomic attack needs to keep its ability to build its own nuclear weapons.
Once, merely the public suggestion that Japan should debate ending its ban on such weaponry was enough to get a politician fired. But worries about North Korea's nuclear ambitions and an expanding Chinese military are eroding that taboo .
Last March's disaster at the Fukushima atomic plant, which spewed radiation and forced mass evacuations, has already prompted Japan to scrap a plan to boost nuclear power to over 50 percent of electricity demand by 2030 from 30 percent before the accident.
But politicians, experts and officials are still arguing over what role -- if any -- nuclear power should play in a new energy mix programme to be unveiled in the summer.
Even the rationales for keeping atomic energy are proving contentious.
"There are people who say that one reason we need nuclear power is in order to have the latent capability for nuclear weapons, from the perspective of national defence," Tatsuo Hatta, an economist who is on an expert panel discussing Japan's future energy mix, told Reuters in a recent interview.
"I think that is one idea but if that is the case, we don't need so many reactors. And the objective should be made clear," he said. "This is not something that should be debated by the trade ministry."
Japan has 54 nuclear reactors, all but three now off-line mainly for safety checks. The rest are due to shut down soon while the government tries to persuade a wary public that it is safe to restart those that pass newly-imposed stress tests.
Shigeru Ishiba, a former defence minister from the now- opposition Liberal Democratic Party, laid out the argument for a latent nuclear deterrent in a magazine article late last year.
"If we had to start from basic research, it would take 5-10 years to create nuclear weapons, but since we have nuclear power technology, it would be possible to create nuclear weapons in the relatively short time of several months to a year," he said.
"And our country has globally leading-edge rocket technology, so if we put these two together, we can achieve effective nuclear weapons in a relatively short time."
Japan's post-World War Two constitution prohibits going to war and, if taken literally, bans the maintenance of a standing army. But successive governments have interpreted the pacifist Article Nine as allowing a military for self-defence.
Since 1957, the official interpretation has also held that Article Nine is not an obstacle to developing nuclear arms even though the concept has long been a political taboo.
"People used to be more reserved about saying it," said Koichi Nakano, a Sophia University political science professor.
"Ishiba isn't saying that Japan should have nuclear weapons but that having the potential is very important to stay in the big leagues and if you don't want to be pushed around by China."
Suggestions Japan might someday use its civilian nuclear technology and stockpile of plutonium -- now totalling about 45 tonnes at home and overseas -- to arm itself with atomic bombs risk fanning concerns by an already suspicious Beijing.
Critics have questioned why Japan stays committed to developing costly nuclear waste reprocessing facilities unless it wants to be able to make atomic bombs should it so decide.
The idea that Japan should have its own nuclear arms, however, is unlikely to gain traction with the majority of the public, whose collective psyche remains scarred by memories of the atomic bombings of Hiroshima and Nagasaki in the final days of World War Two, experts say.
"Japan is the only country that suffered from nuclear weapons. It is a sort of shared understanding that we should use nuclear power only for peaceful uses," said Masakazu Toyoda, head of the Institute of Energy Economics, Japan and a member of the expert panel, who believes Japan needs atomic energy.
As Toyoda's remark suggests, not all supporters of nuclear power -- whose reasons range from the need for energy security in a resource-poor land to a desire to lead in atomic power safety technology, find the latent deterrent argument appealing.
"If Japan considers arming itself with nuclear weapons, then it will find itself in the same situation as Iran and North Korea," Jitsuro Terashima, chairman of the Japan Research Institute and another member of the expert panel, told Reuters.
"Japan's isolation would quickly deepen." (Additional reporting by Kentaro Hamada and Shinichi Saoshiro, Editing by Jonathan Thatcher)