By Tim Kelly and Yukiko Toyoda
NARA, Japan (Reuters) - After a strong showing in an election overshadowed by the killing of former premier Shinzo Abe, Japanese Prime Minister Fumio Kishida may have fresh momentum to hike defence spending on a scale beyond the grasp of his slain mentor.
In doing so, Kishida, a moderate from Hiroshima who wants nuclear weapons banned, would expand on Abe's hawkish legacy and ensure support from Liberal Democratic Party hardliners loyal to Abe.
The LDP's ruling coalition increased its majority in parliament's upper house two days after Abe, the nation's longest-serving premier and a party power broker, was gunned down during a campaign speech in the western city of Nara.
The crime stunned a nation in which gun violence is rare, setting off a wave of mourning and assessments of Abe's legacy. His influence was both far-reaching and polarising, especially on defence. The funeral was set for Tuesday.
Kishida's promise to "substantially" boost defence spending took on new significance after the killing. Seen by some voters as too hawkish, the former premier had never been able to boost defence spending to the 2% of GDP his party has set as a goal.
The next defence budget could be as much as 6 trillion yen ($45 billion), or an increase of 11% from last year, one LDP lawmaker who had been close to Abe and had knowledge of internal defence discussions told Reuters, on condition of anonymity.
"If he can achieve that, the conservatives within the party will flock to Kishida and he will have a long-term administration, no doubt about it," the lawmaker added.
"Kishida can secure his throne by realising Abe's goals."
That conservative support is critical, since Kishida has pursued economic policies that diverge from the neo-liberalism Abe favoured. Control of the factious LDP would allow Kishida three years to execute his programme before another election.
Japanese voters, fearing a slide into militarism, have traditionally been wary of big increases in defence spending, but many now worry that Russia's invasion of Ukraine may embolden China to attack neighbouring Taiwan.
Annual percentage increases of about 10%, the size mentioned by the LDP lawmaker, would double military spending to 2% of GDP by the end of the decade and make Japan the world's third-biggest military spender behind the United States and China.
Beijing now spends more than four times as much as Japan on defence, a ranking of 2021 global defence budgets by the Stockholm International Peace Research Institute shows.
"Kishida is riding a virtually unprecedented wave of support in Japan for increasing the defence budget," said Christopher Johnstone, a senior adviser and Japan chair at the Center for Strategic and International Studies (CSIS).
"There is little controversy about what Kishida has proposed."
Annual increases north of 6 percent to 7 percent are "plausible", Johnstone added.
Abe, who stepped down in 2020 after two terms as prime minister, was elected for his second stint in 2012 pledging to revive the economy and loosen the limits of a pacifist constitution that prevents Japan from waging war.
His cabinet later adopted a resolution to amend the post-World War Two constitution to allow the exercise of collective self-defence, providing the legal basis for expansion of military activities, but he ultimately failed to revise it.
Kishida appears to have less enthusiasm for that goal than Abe - he has said parts of the constitution may have elements that "are outdated and lacking" and hoped discussion on revising it could proceed.
Parties open to revising the constitution maintained their two-thirds majority in the upper house.
Kishida now has a "green light" for more defence spending, said Robert Ward, Japan chair at the International Institute for Strategic Studies.
"Although questions remain over what they'll be spending the money on, where the money will come from," he added.
More than half the respondents in a poll last month by Jiji Press want to see an increase in defence spending. Almost two-thirds said Japan should acquire missiles with sufficient range to strike foreign enemy bases.
Some observers, such as retired admiral Katsutoshi Kawano, a former chief of the Japanese Self-Defence Forces' Joint Staff, want to see bigger spending.
An "appropriate" increase would be about 20% or roughly 1 trillion yen, he said, adding that the extra funds should go to maintenance and logistics to ensure the military can deploy the planes, ships and other fighting assets it already owns.
The military has to cannibalise equipment to keep other systems operational because of a lack of money for spare parts, a former senior defence ministry official told Reuters, asking not to be identified because of the sensitivity of the issue.
Japan will require a decade to build a more potent force that can absorb a doubling of defence spending, with the first three years needed to bring its existing equipment up to scratch and to stock up on munitions, the official said.
Kishida will have to reveal how much he wants to hike defence spending by the end of August and his cabinet will approve the final number at the end of the year.
He is set to release a revised national security strategy and a new five-year military procurement roadmap by year's end.
(Reporting by Tim Kelly in Nara and Yukiko Toyoda in tokyo; Additional reporting by Ju-min Park in Seoul; Editing by David Dolan and Clarence Fernandez)