As a ''sweetener'' for an official American visit in January, Japanese Prime Minister Yasuhiro Nakasone announced his government would finally allow transfers of military technology to the United States.
This announcement - the result of almost two years of strong American public pressure - breached a longstanding ban on the export of anything of a strictly military nature. It was most welcome in Washington as at least a symbol of Japanese willingness to treat a military alliance with the US as a two-way street.
Ever since, however, officials here have been trying to explain just what the promise means and, after weeks of contradictory statements, they have progressed to the stage of establishing just what the US won't be getting: no export of Japanese arms, no joint development of weapons, and no third-country sales of US weapons developed with Japanese technology.
Like all defense-related issues in Japan, this one provides endless opportunities for officialdom to tie itself in knots.
Hiroshi Kitamura, director general of the foreign ministry's American affairs bureau, told the Diet (parliament) that Japan might export arms to the US if requested - later toned down to a ''theoretical possibility'' under the Japan-US security treaty.
Hiroo Kinoshita, a ranking defense agency official, narrowed it down to export of ''experimental weapons'' covered by bilateral technology exchange agreements.
Representing the opposite view, international trade and industry minister Sadanori Yamanaka, emotionally declared Japan would never export arms to any country at any time - also modified by subsequent government statements to tie down only the current Nakasone administration.
This really reflects the constant contradiction in Japan: a pacifist-minded nation with a world-ranking military force and potentially world-ranking arms industry. Japan's arms industry, which until recently had been assessed only on quantitative terms, now is beginning to demonstrate quality as well.
Hence, there is a longstanding official ban on ''military-equipment'' exports , although this has been interpreted to exempt items with civilian as well as military applications - explaining why Japanese cameras could find their way into American ''smart'' bombs dropped during the Vietnam war, for example.
In recent days an argument has also developed that the export ban is overruled in the US case by various bilateral defense agreements.
For the moment, however, this appears to be limited to technology, and even this area is so tightly hemmed in by restrictions as to raise serious doubts about the real effects of the Nakasone promise.
It may come down to Japanese good intentions. ''The fact Japan has been receiving US military technology for years while refusing any transfer in the other direction has become a symbol for Americans of the alleged Japanese 'free ride' on defense,'' notes a foreign ministry official.
Many analysts here doubt Japan has much to offer. ''I cannot think of any Japanese weapons or military technologies that would be more beneficial to the US than American equivalents are,'' commented Jinichi Hirano, executive managing director of the Japan Ordnance Association, grouping 99 arms producers.
Within the local defense industry, desirability of arms exports has been a topic for years: Japan should follow the lead of Western nations in selling arms for Middle East oil; foreign arms sales would enable manufacturers to cut development and production costs and expand profitability, etc.
The industry certainly benefits already from US pressure on Japan for more defense spending. The Japan Ordnance Association says its members in fiscal 1981 produced $2.8 billion worth of equipment, with weapons and aircraft production up more than 20 percent, and this should rise to more than $3 billion in the current fiscal year.
But voices against technology transfers or joint weapons development with the US are on the increase.
There are misgivings that the real American intention is to undercut Japan's competitive advantage over the US in certain high-technology fields (eg: electronics, optics) under the guise of arrangements on military know-how transfers.
There is also fear that the US wants to fit Japan into NATO's ''family weapons system'' so that this country would end up as a subcontractor supplying parts to the US and buying completed weapons in return.
One reason why this fear exists is cited by Hiroshi Morikawa, director of the Defense Production Committee of the Federation of Economic Organisations (Keidanren): ''Even if the ban (on arms exports) were lifted, Japanese-made weapons are too expensive and lack international competitiveness. Also, you have to remember that the weapons have never been battle-tested, so no one knows how good they really are.''
Pointing out that America spends 10 times more of its defense budget on research and development, Mr. Morikawa says: ''In military technology as a whole , or military software, there is a world of difference between the two countries.''
In the aerospace field, for example, Japan has relied heavily on American technology through licensed domestic production of jet fighters and missiles.
Unwittingly, however, the US has helped create a potential rival aircraft industry. From the licensed production of fighters, for example, the Japanese have learned enough to make pretty good civilian jet aircraft for the international market.
In missiles, some Japanese companies now believe they have a superior product - the air-to-surface ASM-1 developed by a group led by Mistubishi Heavy Industries is one frequently cited example.
Japanese-developed electronic miniaturization is beginning to make its mark in such areas as portable missiles. Long distance communications using fiber optic technology is another Japanese strength, along with radar wave absorbers that allow aircraft to escape radar detection.
On the ground, the Japanese soldier still operates with a lot of obsolete equipment, some of Korean War vintage. But at the same time, work is moving ahead fast on a new tank (Type 88) for completion in six years which its developers reckon will be as good as if not better, especially in electronics technology, than anything in the world.
The questions now are whether the US will agree with such confident self-assessments and, if so, whether any of this technology will ever emerge for the taking from the muddy waters of politics.