While successive governments have gradually nudged up military spending each year, they have been able to keep public complaints muted by imposing a ceiling of 1 percent of the gross national product (GNP).
This was easy to do when the Japanese economy was expanding rapidly. But a prolonged business recession and growing government deficits have put this tactic at risk. The 1 percent barrier, in fact, is likely to be breached very shortly as defense spending now accounts for 0.98 percent of the GNP, leading the Defense Agency to propose a new mathematical formula for setting limits.
Some officials have in mind an abstract, basically meaningless, expression such as ''based on minimum necessary defense capabilities.'' The Finance Ministry reportedly opposes the idea, believing it will widen the loophole that already allows defense spending to be increased quite substantially while virtually every other government department is getting less under an austerity program.
In the meantime Washington remains unimpressed as the Japanese fall further behind their own defense buildup goals. As a bare minimum, before the end of this decade, the US wants to see the Japanese with at least 350 modern interceptor fighters, 70 destroyers and frigates, and 25 submarines, and at least 125 new antisubmarine reconnaissance aircraft.
Tokyo's latest defense plan for the years 1983-87 is much more modest, with a goal of between 140 and 155 fighters (American F-15s made here under license), 60 destroyers and frigates with modernized weaponry, and 72 antisubma-rine patrol planes.
But the Defense Agency's original budget requests for fiscal 1983 (starting April 1) were pared down by the Finance Ministry, until it will be able to afford only 13 fighters, 2 destroyers, and 7 patrol planes this year. This would mean double-digit increases in spending each year hereafter to catch up - which is probably politically impossible.
Military wages have been frozen, which helps divert more money to hardware. But even so, experts say the Self-Defense Force is desperately short of ammunition, spare parts, and fuel. There is also insufficient cash available for modernization and development of new weapons systems.
The question is whether scrapping the GNP percentage formula for the defense budget will allow more money to be squeezed out of the system for much-needed improvements without provoking public outcry at a time when spending on other areas (welfare, education, etc.) is being cut back.