Japan's action last weekend in joining the United States and the European allies in a joint statement about international security has stirred controversy in Tokyo and is generating reappraisals here of the island nation's future role in global affairs.

In some respects this event, much discussed by U.S. and European leaders at Williamsburg, has more symbolic than practical meaning. But symbols, especially in this field, are of great importance to everyone concerned.

Item by item, in literal terms, there is little in the seven-paragraph joint declaration that goes beyond the existing policy lines of the Japanese government.

The main new item is that "non-nuclear" and previously pacifistic Japan for the first time joined the United States and NATO nations in making a high-profile statement dealing with East-West security issues, including questions of nuclear negotiations and deployments related to the Soviet Union.

Opposition parties in Japan and some elements of the Japanese media treated Prime Minister Yasuhiro Nakasone's participation in the joint statement as close to a declaration of adherence to the NATO military alliance.

Socialist Party Chairman Ichio Asukata, for example, said the summit statement "confirmed the unification of the U.S.-Japan security treaty and the NATO security relationship."

Nakasone, Foreign Minister Shintaro Abe and their party spokesmen in Tokyo denied that sweeping change has taken place. Appealing to Japanese pride, many private comments and some public comments from Tokyo officialdom stressed that Japan, a crucial economic player at summits but previously a non-participant in security discussions, now has been accepted as a full member of the "West."

At a news conference Monday, Abe said a crucial part of the joint statement in Japanese eyes was the sentence declaring, "The security of our countries is indivisible and must be approached on a global basis." This sentence, according to diplomatic sources, was placed in the declaration at Japan's request.

At one level, the sentence reflects U.S.-European agreement that, as Tokyo has recently insisted, no arms-control deal should permit the Soviet Union to reduce its military power in Europe while increasing its power in Asia.

Statements attributed to Soviet leader Yuri V. Andropov and Foreign Minister Andrei A. Gromyko in January suggested that SS20 nuclear missiles removed from Europe as a result of Euromissile negotiations might be moved to Asia. This stirred alarm in Japan, generating unprecedented public and political interest there in European military issues.

From another perspective, the statement that security is "indivisible" justifies a Japanese role in the security of the West. This is a major departure from Tokyo's previous official premise that its only legitimate military role was in self-defense of the home islands.

This narrow definition of self-defense has actually been eroding for several years, expecially since then-prime minister Zenko Suzuki in a May, 1981, visit here accepted the concept of "burden sharing" in a manner implying a Japanese contribution to a broader and common defense.

This shift was accelerated by the coming to power of the security-minded Nakasone and especially his bold statements here last January that Japan aims to be able to block overflights of the Soviet Backfire bomber and to bottle up the Soviet fleet in the Sea of Japan. Such ideas build on self-defense but go beyond any narrow definition to ambitious strategic consequences.

In a little-noted statement May 9, Tokyo announced that the Maritime Self-Defense Force, the euphemism for the Japanese Navy, is beginning continuous patrols of the Soya strait between the island of Honshu and Soviet-occupied Sakhalin island. This is the most sensitive and strategically important of the nearby straits. The announcement, like Nakasone's statements here, drew verbal blasts from Moscow.

This progression of words and deeds helps explain why Japan's adherence to Sunday's summit statement has been taken so seriously by opponents and proponents of a larger Japanese military role in the world.