The government's surprising defeat in a no-confidence vote threatens a major upheaval in Japan's political world, prompting a widespread suspicion that the era of one-party conservative rule is ending.

The vote that one politician called "The Friday night massacre" raised the possibility that the Liberal Democratic Party may crack in two before the next election. Even if it hangs together, many analysts believe it can rule only as part of a coalition with another party.

There is even the remote possibility, some believe, that Japan, which boasts the world's second-strongest capitalist economy, could be governed a few weeks from now by a socialist-led coalition of the left.

The vote of no-confidence in the government of Prime Minister Masayoshi Ohira was born in his own party's endless factional feuds, but its meaning goes far beyond the skirmishing so familiar in the past decade. Deeply divided and dropping in public opinion polls, the Liberal Democratic Party faces an early election it fears may end 25 years of single-party dominance.

Before Friday's debacle, that test was not expected until near the end of the year, and the dread of an early defeat prompted one Liberal Democrat to recall the British politician's statement: "I never knew a turkey who wanted an early Christmas."

Ohira's government lost the parliamentary vote, 243 to 187, when 69 enemies within his own party abstained, prompted by anger at his refusal to agree to several demands involving party reform. Most of them belonged to factions led by former prime ministers Takeo Fukuda and Takeo Miki. Ohira then was forced to dissolve the lower house and call for new elections.

The government announced today that the election will take place on June 22, simultaneously with the regular upper house election. It will be the first time in postwar history that they take place on the same date.

No mood of reconciliation was apparent today. Three anti-Ohira factions formed a joint committee to plan their strategy and put out the word, taken seriously by Ohira's people, that a new party may be formed. Ohira was under pressure from his own forces to punish the deserters. The party's leadership decided to judge "case by case" whether to deny campaign funds to the defectors.

Even if the party holds together, there will be bitter competition for campaign funds and no central coordination. A loss of only a few seats could mean loss of control. The Liberal Democratic Party now has a majority in the lower house of only one vote, although it can count on the support of six conservative independents in a pinch.

Moreover, the party's popularity has been slipping since last August when, during a political campaign, Ohira unexpectedly began mentioning the necessity of a tax increase. A public opinion poll taken by the Asahi newspapers last week showed that only 43 percent of the people expressed support for the Liberal Democrats, down from 52 percent last August. It was one of the sharpest drops recorded and for the first time support for the opposition parties equaled that for the Liberal Democrats.

If the Liberal Democratic Party lost its majority by only a few seats, it would probably enter a coalition with the Democratic Socialist Party, an equally conservative minor party. If it loses more, it would have to solicit other minor parties. If it loses by a huge margin, there is the possibility of the Japan Socialist Party putting together a big enough coalition to govern.

One prominent political analyst, Takayoshi Miyagawa of the Center for Political Public Relations, flatly predicted today that the Liberal Democratic Party is certain to lose seats in the lower house. "I firmly predict that the days of the one-party rule are over," he said.

Much depends on how Ohira handles the problem of disciplining those in hostile factions who boycotted Friday's vote. Sources said today he does not intend to banish them from the party. But the party leadership, which is loyal to him, could punish them severely by cutting off campaign funds. At the least, the party was expected to call them on the carpet one by one to demand an explanation of their boycott as a price for receiving party money.

Party sources today reconstructed what happened as more of a miscalculation than a deliberate plot by the anti-Ohira groups. The way they described it, it resembled the American game of "chicken" in which two automobiles speed toward each other, each driver waiting for the other to swerve. This time nobody swerved.