* Japan's First Lady suggests cutting waste before raising tax
* Mrs. Abe's "household opposition" could soften PM's image
* Japan's First Lady wants to wean country from nuclear power (Adds details)
By Linda Sieg
TOKYO, Sept 4 (Reuters) - Japanese First Lady Akie Abe - often called the "household opposition" for her penchant to speak out - said on Thursday the country should consider cutting wasteful spending and boosting the economy before going ahead with a rise in the sales tax to 10 percent, as her husband wrestles with just that decision.
Mrs. Abe is a rarity among Japan's First Ladies, most of whom have been largely invisible. The prime minister's skilful PR machine has not silenced her remarks, which could soften the image of a leader seen by detractors as a nationalist with pro-business policies.
"Considering the falling birth rate and ageing society, it probably can't be helped," Akie Abe, 52, told Reuters in an interview on Thursday at the prime minister's official residence, referring to an eventual rise in the sales tax.
"I think there are still areas where, if not a waste, taxes are not being used properly and could probably be fixed," the soft-spoken First Lady added.
"I can understand there are aspects that would be difficult if we don't raise the sales tax, but in my personal opinion, before doing that, shouldn't we put a bit effort into the economy, fix what can be fixed and cut what can be cut?"
But she added: "This won't change just because I say so."
Prime Minister Abe must decide by December whether to proceed with a second-stage rise in the sales tax to 10 percent that is planned for October 2015 to help curb Japan's huge public debt and fund the ballooning costs of its ageing society.
But an initial rise to 8 percent from April triggered a sharp contraction in the economy in the three months to June, raising doubts about whether Abe should go ahead with the hike.
Mrs. Abe said she had urged the prime minister not to raise the levy to 8 percent from April to no avail.
Asked about this time, she said: "I wonder."
Mrs. Abe, the daughter of a confectionary company magnate who married Shinzo Abe when he was an aide to his politician father, said a lot of people opposed many of his policies, such as ending a ban on the military fighting abroad in force since Japan's defeat in World War Two. Some tell her that they worry that the premier is leading the country to war.
"But I tell them that definitely won't happen, so it's okay."
FIRST LADY DIPLOMACY?
Abe has not been held a summit with Chinese President Xi Jinping since taking office due to Sino-Japanese feuds over territory and wartime history. He has called on Xi to meet on the sidelines of an Asian-Pacific leaders gathering November.
Mrs. Abe said she hoped to meet Xi's wife, Peng Liyuan, if possible, even if not one-on-one, since First Ladies could chat without the burden of national interests on their shoulders.
"I felt she is really beautiful and stylish and has an aura," she said, referring to a meeting with Peng last year.
Mrs. Abe accompanies the globe-trotting prime minister on many overseas trips and still has a lingering cough from a cold picked up on their recent marathon trip to Latin America.
In another departure from her husband's policies, Mrs. Abe reiterated that she believed Japan should exit nuclear power if alternate energy sources can be found, given the risks shown by the March 2011 Fukushima disaster, the world's worst atomic accident since Chernobyl.
"Once an accident occurs, it is a terrible thing that cannot be undone," she said. "If there are alternative sources of energy, I would like them to stop (nuclear power). I'd like them not to restart off-line reactors."
But she added that she had not made this point forcefully to her husband because of the delicateness of the issue. Surveys show that many Japanese oppose reactor restarts and a big majority favour at least a gradual exit from atomic power.
Abe's government has said it will proceed with restarting reactors that clear new safety standards.
Mrs. Abe has both won hearts and triggered backlashes for speaking out, but said she had learned not to be as sensitive to criticism as she was when her husband became premier for the first time in 2006. Then, Mrs. Abe said, she felt media were just waiting for her to make a misstep.
"It's not that I don't mind at all," she said. "But in a sense, I am doing this out of my own convictions, so I think it's okay to say what I want to say."
Abe ended his first troubled term after just one year due to ill-health and political deadlock. He staged a comeback in December 2012, promising to revive the stagnant economy and bolster security.
Mrs. Abe said that the prime minister says he's now in better health than ever due to medicine, approved in Japan after he resigned, that he takes for chronic intestinal illness.
He can now drink alcohol when he meets close friends, though he is by no means a big drinker.
"The important thing is not to build up stress," she said. "He does things like watching DVDs by himself and I don't bother him when he's taking time alone." (Additional reporting by Jiro Minier; Editing by Nick Macfie)