To cries of "banzai" from a flag-waving crowd of several hundred, Yasuhiro Nakasone stepped into the crisp autumn sunshine of an ancient temple courtyard here the other day to press his campaign bid to become Japan's 16th prime minister since World War II.

Tall and magisterial, Nakasone, 64, is touted by Japanese pollsters as the odds-on favorite to win elections next week for Liberal Democratic Party (LDP) president, a post that carries with it the premiership because of the party's large majority in the country's parliament.

Nakasone's whistle-stop tour here in rural Japan has all the outward trappings of electioneering familiar to most Americans. LDP faithfuls, who belong to the party's 1 million rank-and-file membership voting in the Nov. 24 primary, drink beer and soft drinks provided by local Nakasone boosters. They listen attentively as the candidate promises to lead the country to more of the prosperity that has been a fact of Japanese life since the Liberal Democrats came to power 27 years ago.

Beyond the fanfare and mudslinging typical of this hotly contested campaign, however, is a big gulf between the political practices of Japan and the United States. In Japan, party politics operate in a web of social customs and backroom wheeling and dealing among shrewd LDP barons that gives them the flavor of the old-fashioned ward politics in a big American city, where money and personal connections do much of the talking.

The LDP's complex machinery for primary elections was set in motion in October amid a bruising fight among party factions that forced Prime Minister Zenko Suzuki to abruptly announce his decision to step aside, pending the selection of a new leader. The four-way race pits Nakasone, director general of the government's administrative management agency, against Toshio Komoto, 71, Ichiro Nakagawa, 57, and Shintaro Abe, 58, who also are senior members of the Suzuki Cabinet.

According to newspaper samplings of LDP voters nationwide, Nakasone is now expected to score a commanding victory when primary ballots are counted next Wednesday, although interviews with local ward captains in Tokyo suggest that Komoto may cut deeply into that lead. A new party leader will then be selected the following day by LDP members in the Diet, or parliament, from among the top three finalists. If all goes smoothly, a session of the LDP-controlled Diet, now scheduled for Nov. 26, will approve the party president as prime minister.

Behind the scenes, however, the voting is said to be dominated by the power plays of former prime ministers Kakuei Tanaka and Takeo Fukuda, bitter political foes who control the party's two key wings. Tanaka, who was forced to resign official LDP membership because of his involvement in the Lockheed bribery scandal, runs by proxy the party's largest Diet faction and is reputed to command a vast and shadowy army of well-heeled patrons.

Tanaka, who is widely regarded as having been the power behind the Suzuki throne, has thrown his support to Nakasone. Fukuda has marshalled his forces behind Komoto in a battle designed to break Tanaka's pervasive hold on power.

The "Kaku-Fuku war," named for the years-long feud between the two politicians, helps explain the shifting loyalties and smoldering antagonisms within the LDP that often confound foreign observers. The largely pro-American LDP is, in fact, a loose coalition of factions ruled by party bosses who exact feudal-style allegiances from their followers. In return, they dole out the campaign funds and key political connections that help get their juniors elected to the Diet.

At the center are Tanaka and Fukuda, who manipulate the levers of money and power and strike the deals that make possible Japan's system of politics by consensus. In contrast to the more individualistic flair of American party politics, the rigid LDP hierarchy has a strong emotional appeal here because of a centuries-old tradition of group loyalty that is important in all facets of Japanese life. Japan's storied past is replete with emperors' regents and samurai warlords who ruled the country from the wings.

Many of today's ambitious, younger politicians chafe over the prerogatives of the LDP's old-boy network, which they view as having kept them from rising quickly enough to top party and government posts. But they shrink from cutting their umbilical ties with the factions in a system where, it is said, it takes upwards of $1 million to get elected to the Diet.

Because of the way voting districts are laid out in Japan, the LDP relies heavily on the votes of farmers, fishermen and white-collar workers, while the country's business interests provide the bulk of the party's financial support. Only party kingmakers like Tanaka and Fukuda have the vast personal connections that help ensure success at the polls.

The knock-down, drag-out fight among LDP rivals that led to Suzuki's decision to bow out ostensibly was waged on the grounds that Suzuki had failed to make good on campaign promises to cut back on Tokyo's bulging deficits by streamlining the government bureaucracy. Suzuki also was chided by Komoto, Abe and others for tight-fisted fiscal policies that they charged seriously damaged the performance of Japan's flagging economy.

In the primary campaign, however, the heated endorsement of policy preferences quickly dissolved. The actual differences of opinion among the candidates on key issues remain matters of delicate nuances.

Nakasone, whose current Cabinet post charges him with overseeing reform of key government departments, stresses the need to trim the fat from the national budget. At the same time, he has tacitly supported the need to use public spending to revive Japan's domestic economy and open the way for tax increases to help flatten government debt. Komoto, a corporate president turned politican, has reversed the priorities, but the net effect is largely the same.

In Japan, practically all important decisions on public policy are made by the nation's senior career bureaucrats. Japanese legislators -- and prime ministers -- have no large staffs of their own and must rely heavily on the administrators.

Whatever the outcome of next week's elections, the new prime minister will be bound by these built-in constraints, which make it difficult for any national leader to do more than help shape a consensus among competing public interest groups and steer bureaucratic subordinates toward a final decision. Nakasone, for example, is known in the pro-business, largely pro-American establishment here as a hawk on national defense issues. But he is not likely to be able, or willing, to set Japan on a course toward the sizable boosts in military spending the Reagan administration would like to see.

Over the years, Nakasone has acquired the nickname of "Weathervane" among many voters for his careful calculation of the direction of the political winds.

Reflecting on the deft maneuvering essential to survival in party politics here, Nakasone said in a recent interview, "The LDP tradition is one of flexibility. . . . The party has shifted to the right, to the left and back to center to adapt to the demands of each new era. That's the way [it] has been able to maintain its ruling power."