TOKYO (Reuters) - A fast-growing challenge by Tokyo’s governor, often floated as Japan’s first possible female premier, to Shinzo Abe’s ruling bloc has highlighted the risk of his gamble on a snap poll as she tries to replicate a historic defeat of his party.

Japan's Prime Minister Shinzo Abe makes his fist as he speaks to his party's lawmakers at the party lawmakers' meeting, after the dissolution of the lower house was announced at the Parliament in Tokyo, Japan September 28, 2017. REUTERS/Kim Kyung-Hoon

Abe called the Oct. 22 election in the hope his improved ratings and a struggling opposition would help his Liberal Democratic Party-led coalition keep its majority in the lower house, where it now holds a two-thirds “super majority”.

But Abe’s bet now looks increasingly shaky, given growing support for Yuriko Koike’s fledgling “Party of Hope” - launched this week - and the opposition Democratic Party’s move to have its candidates leave the party and run on her ticket.

No general election needed to be held until late 2018.

Abe’s decision has evoked comparison’s to British Prime Minister Theresa May’s move to call a snap election in June, only to see her Conservative Party lose its overall majority, although analysts noted Koike might have become an even bigger threat had Abe waited.

“Abe thought the risk worth taking. Maybe he didn’t anticipate what Koike would do,” said Daniel Sneider, a Stanford University scholar currently doing research in Japan.

The growing momentum of Koike’s party has also revived memories of a 1993 political drama when a coalition led by another reformist governor, Morihiro Hosokawa, ousted the LDP for the first time since its founding four decades earlier.

Clearly, the historical parallels are weighing on Abe’s mind. Abe, Koike and Democratic Party leader Seiji Maehara were elected to the lower house for the first time that year, Koike and Maehara from Hosokawa’s Japan New Party and Abe from the LDP.

“There was a new party boom in the 1990s and the result was political confusion and a long period of economic stagnation,” Abe said in a campaign speech on Thursday. Hosokawa’s fractious alliance fractured after less than one year.

“CONFUSION VS HOPE”

Abe also cited the 2009-12 rule of the Democratic Party, whose policy flip-flops and infighting many voters recall.

“What would be born of a (new party) boom is confusion, not hope,” Abe said.

Another key player in 1993, Ichiro Ozawa, who bolted the LDP and helped engineer Hosokawa’s coalition as well as the Democratic Party’s 2009 surge to power, is also playing a role now. His tiny Liberal Party may also merge with Koike’s party.

Like anti-LDP forces in 1993 and the Democrats in 2009, Koike is promising to “shed the shackles of vested interests” - a slogan appealing to voters seeking an alternative to the LDP.

Former prime minister Junichiro Koizumi - who mentored Koike after she later joined the LDP - also skilfully painted the old guard in his own party as obstacles to reform in a 2005 election, winning a massive victory.

To succeed, however, Koike may have to take a big gamble of her own by running in the election herself, risking a backlash for quitting as governor and ending up an opposition leader.Koike, who compares herself to French President Emmanuel Macron and his meteoric rise, has repeatedly said she’ll stay on as governor, but her carefully parsed comments have failed to dampen speculation.

“Ms. Koike is saying she won’t run, but ... I think she will run,” Chief Cabinet Secretary Yoshihide Suga told reporters on Friday, one day after Abe called the lower house poll.

“It would be great if she announced that boldly and debated policies head on,” he added, in an apparent challenge.

Despite Koike’s efforts to broaden her party base by absorbing many Democratic Party candidates, fielding a big enough slate to take a majority in the 465-member lower house could be tough. Candidates must register on Oct. 10.

She said on Friday she won’t accept all Democrats who want to run on her ticket, and liberals will probably be left out.

Even if Koike, who defied the LDP to run for governor last year and whose local party trounced it in a July Tokyo assembly election, decides not to run herself, her party’s challenge can still weaken Abe if the LDP fares badly.

“If the LDP loses 40 seats or more, she looks good,” said Columbia University professor emeritus Gerry Curtis.