Japan's rebuke

The rebuke Japanese voters dealt Prime Minister Yasuhiro Nakasone's Liberal Democratic Party - stripping the LDP of its outright majority in Sunday's elections, forcing it to depend on independents for only the second time in its 26-year reign to keep power - has several aspects.

First, most obviously, it reflected dissatisfaction over the Tanaka-Lockheed scandal. Former Prime Minister Kakuei Tanaka, an LDP member and a Japanese political operative of great power, was recently convicted of taking a $2 million bribe from Lockheed Corporation. Tanaka refused to resign his parliamentary seat. So Prime Minister Nakasone, to quell criticism for not seeking Tanaka's ouster, called the general election six months ahead of schedule. The election maneuver backfired. Tanaka was returned to office by his district's voters with a larger margin than Nakasone's.

Second, the election showed an American president's political coattails can be as short and insubstantial abroad as at home. Mr. Reagan's Japan trip in November was ostensibly designed to shore up Mr. Nakasone in his election bid, emphasizing Japan's role as a modern world power. Mr. Nakasone certainly played the visit that way. But the fact is, the Japanese electorate may be more worried about the course of US policy, both in regard to Japan and more generally in the region, than is usually noted. Reagan's pressure to get Japan to increase its defense spending - which Nakasone has sought to accommodate - troubles many voters. So does Mr. Reagan's approach to world affairs, which strikes many Japanese as increasingly assertive.

Third, the election revealed again that Japan has a relatively ''weak'' political structure that appears inadequate to its world economic ambitions.

This is the most troubling aspect of the Japanese election. Japan's political system was deliberately designed, after its military defeat nearly four decades ago, to be weak. Japan is tied to the United States for its security by a constitutional prohibition against rearming. Factional maneuvering - who knows how far Tanaka's resurgence will take him? - has long been endemic in a society where the politics of warlords and influence-wielding have left an imprint.

Japan's business leaders, it would appear, want to take the nation on a primarily mercantilist course. Economic expansion appears to be sought for its own sake, without even some corresponding enjoyment of the fruits of expansion. Earnings and savings are plowed back in for more expansion.

The election suggests that Japan, for all its economic prowess, remains a country without any other commanding political objectives. Mr. Nakasone's challenge - to deal with the powerful Tanaka faction and achieve some semblance of party unity - becomes all the more critical in light of the mismatch between Japan's weighty world presence and delicate domestic political framework.