He spends Wednesdays in a Tokyo courtroom where he stands accused of accepting a $2.5 million bribe for allegedly influencing the sales in Japan of Lockheed jets.

But on other days of the week, former prime minister Kakuei Tanaka is deeply involved in the politics of Japan, shaping governments and influencing the men who run them.

Five years after he was arrested in the Lockheed scandal, Tanaka heads the largest faction in the ruling Liberal Democratic Party -- even though he left that party in disgrace and is still not a member. With his approval, an unknown named Zenko Suzuki became prime minister last year.

Scores of politicians and favor-seekers come every day to his estate in the Mejiro section of Tokyo seeking counsel. Candidates covet his support in Tokyo's current municipal elections. The press calls him "the dark general of Mejiro" and imputes to him a vast, shadowy influence on every corner of political life.

"In the press," observes one member of parliament, "Mejiro becomes the reason behind all things that are unexplainable in politics. In socialist countries, Marxism is supposed to explain everything that happens. In Japan, Tanakaism is like Marxism."

In an interview, Tanaka scoffed at the public assumption that he runs the Suzuki government from behind the scenes. Not once since he became prime minister has Suzuki consulted him ona substantive matter, he said. Suzuki, he said, "in no way speaks on my behalf."

But Tanaka was quick to point out the importance of his faction, which includes about a fourth of all party members in parliament. He listed several fctional members of influence in Suzuki's Cabinet and summed it up by saying, "So we believe we have a very good channel of communication with the current administration."

At 63, Tanaka still exudes the personal force and sense of restless energy that made him a Wunderkind of Japanese politics -- a country boy who with charm, favors and relentless striving bowled over rivals to become prime minister the hard way. "The computerized bulldozer," he was once called.

Elected in 1972, he was forced to resign in disgrace two years later after a leading magazine, Bungei Shunju, published a searching analysis of his financial affairs, alleging in part that he had used political money for private purposes.

In July 1976, he was arrested on a charge that in 1972 he accepted 500 million yen from a Japanese trading company, Marubeni, acting in behalf of Lockheed, which was endeavoring to sell its Tristar jets to a Japanese airline. At the time the bribes were allegedly being passed Tanaka was carrying out his official duties such as meeting with former president Nixon. Tanaka has denied the charge. Testimony in court alleges the money was paid in four cash installments through his personal secretary.

Tanaka declined to discuss his trial during the interview, and his recollections of past troubles are elegantly phrased in a semi-joking manner to brush past painful questions. He resigned from the Liberal Democratic Party after being arrested in the Lockheed scandal. The way he recalls it, "I left the [party] at my own initiative when I caught 'the American cold'."

How, he was asked, could he take part in the party's largest faction when he is not even a party member? Without a trace of hesitation, he replied, "It is only in legal terms that I am not a member of the [party] and all members of the [party] consider myself nothing but [a] member."

He attributes his lingering influence in part to the continued close contacts with members of the parliament and Japan's provincial legislatures. He says he has served with the fathers and grandfathers of many present members and knew a third of the party's present parliament members when they were college students.

Although he is thought to be short of funds, Tanaka still maintains a lavish residence and office in Mejiro, with a considerable staff. Other soources said corporate money ceased to flow to him when he was indicted, but top lieutenants in his faction are still able to collect funds from businesses. t

Factional groupings within the party are the keys to power in Japan and the faction that still bears Tanaka's name -- The Thursday Club -- has not withered. If anything, it has grown larger. It now has at least 103 members, and Tanaka claimed this week that about 20 other parliament members loyal to him are hidden awy in other factions, waiting to support him if necessary. It is easily large enough to at least veto a prime ministerial candidate, if not to name one.

Personal loyalties from years back account partly for his continued factional support. It is shameful in Japan to cut and run when the boss stumbles.

"There is a strong feeling in the [party] that if you belong to a faction, you must stick with it even if it is in trouble," observed one parliament member not allied with Tanaka.

There is also, some critics say, a rather cavalier attitude toward political corruption. Corporate money flows easily to Japanese politicians, and many accept it as a natural way of life.

"Japanese people think that all politicians do the same thing that Tanaka did," said Takashi Tachibana, the writer who led the magazine team in exposing Tanaka's financial dealings eight years ago. "It is strongly accepted in the political world that money politics is okay."

Tanaka brushes aside the political money charges as if they were inconsequential. "Newspapers talk a lot about money ties, but they inestigated and found out there was no such thing," he said.

Tanaka's position as de factor factional chief also makes him a power within the government bureaucracy, according to Tachibana.

Tanaka's trial, which began in January 1977, still has many months to run, but the political gossip mill already churns with speculation about what he will do if he is acquitted. At 63, he is still young enough to build a new campaign for the premiership. Tanaka, in the interview, insisted he would not actively seek the post again, contending that it could only come if the party offered it to him.

Would he accept it if offered?

"I do not answer hypothetical questions," Tanaka said.