IN Japan, prime ministers come and go, but a single party remains in power: the Liberal Democrats (LDP). A political system in which the opposition never has a chance to come out of the wilderness is only half a democracy. There are finally signs that the pattern may be about to change.
When former Prime Minister Yasuhiro Nakasone was a fledgling member of parliament just after World War II, he plastered his mainly rural constituency with billboards calling for the prime minister to be elected by all the people. After many years, the LDP devised a primary in which ordinary party members could vote for the candidate of their choice. It was a kind of popularity poll, with no binding power on members of parliament, who constitutionally are the only ones who can elect a new prime minister. A couple of elections were held under this system. In the first, in 1978, Prime Minister Takeo Fukuda suffered an unexpected defeat at the hands of his rival, Masayoshi Ohira. Having promised to abide by the primary results, he had to resign.
But the LDP was never comfortable with popular voting, and soon went back to its previous system of voting restricted to members of parliament and selected representatives from the provinces. That is how Kiichi Miyazawa succeeded Toshiki Kaifu as prime minister last fall.
Japan, like Britain, is a parliamentary democracy: The prime minister is the leader of the majority party in parliament. If opposition parties were stronger, there would be no legal obstacle to their wresting power from the LDP. But the principal opposition party, the Socialists, is an ideological anachronism, and the others appeal only to narrow niches: the Komeito (based on an iconoclastic Buddhist sect), the Democratic Socialists (a moderate offshoot of the Socialists), and the Communists.
The first signs of change in this long-established system came in 1986, when, after a particularly severe election defeat, the Socialists for the first time chose a woman leader, Takako Doi. Like her colleagues, she is an ideologue opposed to the alliance with the United States. But she soft-pedaled this stand, emphasized unity with the Komeito and the Democratic Socialists, and vigorously promoted women candidates for office. Helped by a blockbuster scandal, the so-called Recruit case which touched almo s t every major LDP politician, the opposition parties swept to victory in upper-house elections in 1989.
Under the Japanese constitution, the lower house can overrule the upper house on three major items: the election of the prime minister, the budget, and international treaties. For the time being, the Liberal Democrats were safe. But in order to get major legislation passed, they needed the cooperation of at least one opposition party. Their preferred partners were the Komeito and the Democratic Socialists. But whenever a particularly controversial issue such as joining United Nations peacekeeping forces came up, the ad hoc coalition splintered.
This year, there is a new scandal, and another upper-house election will take place in July. Ms. Doi has been succeeded by Makoto Tanabe. Mr. Tanabe, one of the few Christians in Japanese politics, has less charisma than Doi but is much more conscious of the need to modernize Socialist policies. He is on good terms with the LDP's eminence grise, Shin Kanemaru.
The LDP recently lost an important by-election, and most commentators expect it to lose the election this summer as well. As long as it controls the lower house, where elections are not required until 1994, it can retain the prime ministership. But to break the legislative logjam, LDP leaders have talked of creating a broad-based coalition, perhaps even a grand coalition with the Socialists, as Germany's Christian Democrats did in the 1960s.
That could finally open the door, as in Germany, to what Japan has lacked in the postwar years: alternation of political power.