Japan's political campaigns look like those in US -- but not quite

''It's a bit like the Mafia choosing a new godfather.''

With this scathing comment, the middle-aged Japanese businessman interviewed enroute to work dismissed the current campaign by four leading lights of the Liberal Democratic Party (LDP) to gain the party's presidency and with it the right to be prime minister.

''It's got nothing to do with us because we aren't being consulted,'' said a secretary. ''And whoever wins, it will still be the same old group of politicians running things.''

With Prime Minister Zenko Suzuki's surprise decision last month to resign, the factions in his party are feuding bitterly over the succession. For 35 years the only political change Japan has seen is the ascendancy of one LDP faction or another. In 1972, for instance, Kakuei Tanaka spent a fortune to win enough votes from LDP members of the Diet (parliament) to beat Takeo Fukuda.

Public outcry over the dominance of ''money politics'' led party bosses in 1978 to institute a ''more democratic system.'' As there were sufficient candidates, a primary election was held involving all registered party members. The top two vote-getters faced a runoff vote involving only LDP Dietmen, making it a rather narrow exercise in democracy. Now the LDP is going the primary route a second time.

The rules have been changed a bit. Three candidates will go forward to the runoff vote by Dietmen alone. The candidates have been allowed to buy from party headquarters for approximately $12,500 each a list of the LDP membership to make canvassing easier. (Last time, the names were kept secret in the hopes of avoiding vote-buying.)

There are some superficial resemblances in the campaign to American primary elections. Dietmen have returned to their home districts to drum up support for the candidate they favor. There is considerable vote canvassing by telephone and mail.

The candidates are making nationwide stumping tours, lecturing on the need for a ''fresh approach'' to the nation's many problems and the need for a revival of ''political morality.'' National personalities from the sporting or show-business world provide visual support in the clips that make their way onto the national television news each night.

But there are substantial differences between the Japanese and US primaries. An American political analyst says:

''The US primary elections are very much a popular vote because basically every adult who has registered to vote - and been designated either Democrat or Republican - is eligible to participate even if they usually don't do so. The LDP election, however, is a much narrower vote appealing to a much smaller segment of the population, namely, the 1,045,000 people who are registered as LDP supporters.''

But even the LDP members don't have a big say in the final result. They select three candidates for final voting by the 421 LDP members of the two houses of the Diet. Even here, the influence of a handful of factional bosses - controlling the cash for election campaigns and distribution of top government and party posts - will be decisive.

Therefore, the analyst said, the LDP primary is more of a secondary election than anything seen in the United States. Public opinion is far removed from the final result.

Conversations with a cross-section of Japanese reveal indifference or disgust at this type of political process. The letter columns of national newspapers have been crammed with complaints about the system. They often end in the suggestion it is time the entire nation was allowed to participate.

For the American political student, however, the current campaign is fascinating. There is, for example, the possibility of the leading vote-getter in the primary being deposed in the runoff due to the factional mechanism - recalling concerns in the 1976 Carter-Ford election that the winner of the popular vote could lose in the electoral college.

This is a very real possibility. When the postal votes are counted Nov. 24, it is considered highly likely that Toshio Komoto, present head of the economic planning agency, will emerge on top. He has worked hard for four years to develop a strong grass-roots organization at great expense.

But when the Dietmen vote the next day, his support should shrink considerably. Yasuhiro Nakasone is expected to have at least two-thirds of the votes in the runoff if he survives the primary.

Nakasone's rivals hammer away at this point, saying the LDP will continue to be controlled by ''outside interests'' - a clear reference to former Prime Minister Tanaka, who retains remarkable influence despite quitting his post and the party in successive scandals over his financial dealings and then involvement in the Lockheed bribes case.

Unlike general elections, the public office election law - which tightly proscribes campaign activities, including banning door-to-door canvassing and setting limits on spending - does not apply in the LDP primary.

Estimates vary on how much the campaign will cost. Cynics claim that during LDP internal elections there is always a shortage of one local whiskey, as the box it comes in is the right size for the insertion of 10 million yen in bank notes - allegedly the standard rate as a ''thank you for your support.''