TOKYO (Reuters) - A new political party led by Tokyo Governor Yuriko Koike is floating populist slogans such as ending nuclear power and freezing a sales tax hike ahead of a general election next month, but voters may find few other big policy gaps with the ruling Liberal Democratic Party (LDP).

Koike’s Party of Hope, formally launched on Wednesday with a slick promotion video and news conference, could attract voters who feel Prime Minister Shinzo Abe has become complacent, even arrogant, after nearly five years in office.

The new party adds more uncertainty to the election.

Abe’s LDP-led coalition is unlikely to lose its grip on power, but a weak showing would erode Abe’s clout, make policy initiatives harder and jeopardize his hopes of becoming Japan’s longest-serving premier.

“There’s not much daylight between Koike’s party and the LDP,” said Gerry Curtis, professor emeritus at Columbia University in New York. “It’s a question of who can impress the voters as more competent. It’s competence and it’s character.”

The Party of Hope shares policy space with both the conservative, business-friendly LDP and the right wing of the main opposition Democratic Party, an often fractious mix of conservatives and liberals.

The Democrats are struggling with defections to the new party and single-digit ratings.

Asked about media reports that she discussed a merger or tie-up with the Democrats’ leader, Koike told public broadcaster NHK she was not interested.

“Rather than party to party, I welcome participation by individuals who share our policies,” she said, adding her party had been approached by many would-be candidates.

Some political analysts suggest Koike might opt to ally with the LDP after the election, given their policy similarities.

Abe, promising strong leadership to cope with Japan’s fast-ageing population and a rising threat from North Korea, is betting the LDP and its junior coalition partner can keep their majority in parliament’s lower house, where they hold a two-thirds “super majority”. He will dissolve the lower house on Thursday for a vote expected on Oct. 22.

The 63-year-old premier returned to power in December 2012 for a rare second term, promising to bolster Japan’s defense and reboot its deflation-plagued economy with hyper-easy monetary policy, spending and reforms. He has made revising the post-war, pacifist constitution a key plank in his long-term agenda.

Koike, 65, served as defense minister in Abe’s first 2006-07 cabinet, but she defied the LDP to run successfully for Tokyo governor last year and, in July, her novice local party handed the LDP an historic defeat in a Tokyo assembly poll.

The media-savvy former TV announcer - often floated as a candidate to become Japan’s first female premier - is looking to repeat that success nationally. She said on Wednesday, though, that she wouldn’t run for parliament this time.

A vague Party of Hope platform unveiled on Wednesday pledged to be a “tolerant, conservative reform party,” break free of vested interests, protect the public, spend tax money wisely and respect diversity.

SALES TAX, NUCLEAR POWER

Koike has, however, distanced herself from the LDP on two issues that could resonate with voters.

She has suggested freezing a rise in the sales tax to 10 percent from 8 percent, from 2019, and called for an end to nuclear power - without saying how or by when.

The latter issue has sparked speculation Koike could win the backing from once popular former prime minister Junichiro Koizumi, who advocates an immediate end to atomic energy.

Abe, in contrast, says he’ll go ahead with the tax hike but divert some revenue to childcare and education instead of paying back public debt. His government plans to keep atomic power as a basic energy source despite public concerns after the 2011 Fukushima nuclear crisis.

Koike has criticized the prime minister’s “Abenomics” growth policy for not making people feel good, but she has not outlined what she’d do instead, except speed up reform.

Both Abe and Koike are hawkish on security policy, although she has said little lately except to pledge “practical diplomacy and security policy based on pacifism”.

She has said debate was inevitable on revising the post-war constitution, but should not be limited to the divisive issue of amending pacifist Article 9, which Abe wants to change to clarify the military’s status.

Promises to reform “vested interest politics” and end governance through back-room deals often resonate with Japanese voters, who periodically long for change from the LDP, which has ruled Japan for most of the past six decades.