TOKYO — ON Sunday, Japanese voters will have a major opportunity to amplify the mandate for change they issued two years ago when they rejected the political party that had led this country's government for 38 of the 50 years after World War II.
But to listen to the conventional wisdom in Tokyo, the voters may very well say, ''Forget about it,'' and set in motion a series of events that will mean the resurgence of the Liberal Democratic Party (LDP), the political institution they turned against in July 1993.
In that case it will be time to put a match to the reams of analysis about Japan's political ''revolution,'' creating bonfires that will burn long into the night. It will mean the LDP will have succeeded in restyling itself to please the electorate and in outmaneuvering its political rivals.
Normally the level of excitement over elections for the upper house of Japan's parliament is matched by the insignificance of the legislative body itself, which serves largely as an appendage of the decisionmaking lower house.
Analysts expect low voter turnout in Sunday's elections, which will fill half of the upper house's 252 seats.
But the political class here is watching the races closely.
One reason is that this election is the first under electoral laws instituted in the wave of enthusiasm for political reform that ousted the LDP. Where Japan used to be divided into large districts that sent several representatives to parliament, the political geography has been redrawn to provide some single-seat districts designed to make the voters' political will clearer.
And as always in politics, there is an element of uncertainty. Voters in Tokyo and Osaka, the country's two most important cities, stunned the established political parties in April by electing two iconoclastic independents as the cities' governors.
''I think the people do want change in their hearts,'' says Morihiro Hosokawa, a reformer and one-time prime minister, ''But I think they are saying they can't go on with the present situation and that is why they elected [Tokyo Gov. Yukio] Aoshima.''
A year ago the LDP effectively returned to power, capitalizing on the inability of reformist politicians such as Mr. Hosokawa to create a functioning government in the wake of the 1993 upset. LDP members now dominate a coalition government led by Prime Minister Tomiichi Murayama, a Socialist whose cooperation with the LDP has forced him to rewrite or annul many of his party's policies.
Meanwhile, the opposition parties who collectively defeated the LDP in 1993 have joined together as the New Frontier Party but have found themselves unable to coalesce into a meaningful political force.
Japanese voters have been watching this process with increasing apathy. The politicians, after all, are starting to make Nero look good. Tokyo isn't burning yet, but the Japanese economy has been getting worse despite official assurances that it is on the mend. An increasing number of Japanese, especially women, have been unable to find jobs.
This spring's spate of urban terror has caused some to wonder where their leaders are, and Japan's international relationships are getting more complex as China grows more powerful and the US more distant.
Mr. Murayama's Social Democratic Party is the most vulnerable going into Sunday's race. His abandonment of the SDP's pacifist positions of the cold-war era has alienated many Socialist backers. Murayama has said it will be a victory if his party captures 22 seats, but most analysts expect it to win around 15.
Even so, he will likely get to keep his job for a while longer. ''Common sense tells us that Murayama will stay until the end of this year,'' says political analyst Minoru Morita. For one thing, his LDP backers need Murayama to provide cover until they resolve some internal leadership questions.
The LDP is headed by Foreign Minister Yohei Kono, but Trade Minister Ryutaro Hashimoto is expected to challenge Mr. Kono in a party leadership contest this September. Looming in the distance are elections for the all-important lower house, which analysts expect anytime in the next 10 months. The LDP must decide how to portray itself in those races: as the party in charge or with Murayama to take the blame for failures of leadership.
Either way, in the view of pollster Takayoshi Miyagawa, the party's prospects look good. ''I expect a landslide victory for the LDP in the next Lower House elections,'' he says.
Mr. Morita says that no conclusions can be drawn until that event. There is still time, he argues, for the opposition New Frontier Party to revamp its leadership, perhaps under former Prime Minister Hosokawa, and squarely challenge the LDP.