* Abe may lose "super majority" but still form govt
* Korean tensions boost Abe's leadership credentials
* Ruling party says "no political vacuum" during campaign
* Abe to order 2 trln yen package for child care, education
* "Nasty surprises" can't be ruled out - analysts
* Tokyo Governor Koike launches new "Party of Hope" (Adds Abe informed ruling party of election plan)
TOKYO, Sept 25 (Reuters) - Japanese Prime Minister Shinzo Abe will dissolve parliament's lower house on Thursday for a snap election, a party official said, in a move aimed at taking advantage of improved ratings and opposition disarray.
Abe's junior coalition partner Natuo Yamaguchi, the head of the Komeito party, said he understood that the election will be held on Oct. 22, as Abe prepared to hold a news conference at 6 p.m. (0900 GMT) on Monday.
Abe, who has held power for five years, was expected to put pledges to spend on education and child care, stay tough on North Korea and revise the constitution at the forefront of his campaign.
Abe, whose ratings have risen to around 50 percent from around 30 percent in July, is gambling his ruling bloc can keep its lower house majority even if they lose the two-thirds "super majority" needed to achieve his long-held goal of revising the post-war pacifist constitution to clarify the military's role.
A weekend survey by the Nikkei business daily survey showed 44 percent of voters planned to vote for Abe's Liberal Democratic Party (LDP) versus 8 percent for the main opposition Democratic Party and another 8 percent for a new party launched by popular Tokyo Governor Yuriko Koike.
The Nikkei poll was far more positive for Abe's prospects that a Kyodo news agency survey that showed his LDP garnering 27.7 percent support, with 42.2 percent undecided.
Abe's image as a strong leader has bolstered his ratings amid rising tensions over North Korea's nuclear arms and missile programmes and overshadowed opposition criticism of the premier for suspected cronyism scandals that had eroded his support.
Some critics say that Abe has risked creating a political vacuum at a time when geo-political tensions over North Korea are rising.
And, given the unexpected results seen in other major developed countries, political analysts are not ruling a "nasty surprise" for the Japanese leader.
"Abe's big gamble could yield a big surprise," veteran independent political analysts Minoru Morita said.
Abe told LDP executives at a meeting on Monday that he intended to dissolve the lower house on Thursday. The prime minister had been expected to face a grilling over the cronyism scandals during Thursday's session, and opposition party officials saw the move as play to avoid difficult questions.
Sources have said Abe's election platform will see him promise to go ahead with a planned rise in the national sales tax to 10 percent from 8 percent in 2019 but increase the proportion of revenue spent on child care and education, delaying a target of putting the budget in the black in the fiscal year ending March 2021.
Abe on Monday asked his cabinet to compile a 2 trillion yen ($17.80 billion) economic package by the year-end to focus on child care, education and encouraging corporate investment, while maintaining fiscal discipline.
The Yomiuri newspaper said earlier the funding would cover the three years from April 2018 until sales tax revenue kicks in.
The main opposition Democratic Party is struggling with single-digit ratings and much depends on whether it can cooperate with liberal opposition groups.
Tokyo Governor Yuriko Koike announced on Monday - just hours ahead of Abe's news conference - that she would lead a new conservative, reform-minded "Party of Hope" to provide voters with an alternative to the LDP.
"Our ideal is to proceed free of special interests," Koike, a former LDP member, told a news conference.
A junior cabinet minister from the LDP, Mineyuki Fukuda, said over the weekend he would leave the ruling party to stand for election with Koike's new group.
An LDP internal survey showed seats held by the LDP and its coalition partner Komeito could fall to 280 from the 323 they now hold, the Nikkei reported on Saturday. Reforms enacted last year will cut the number of lower house seats to 465 from 475.
($1 = 112.3400 yen) (Additional reporting by Takashi Umekawa, Stanley White and Tim Kelly; Editing by Michael Perry & Simon Cameron-Moore)