A Tokyo district court today sentenced billionaire Japanese businessman Kenji Osano, a longtime associate of former prime minister Kakuei Tanaka, to a year in prison for his role in the 5-year-old Lockheed bribery scandal.

In separate court proceedings, Tanaka is accused of accepting a $2.2 million bribe for allegedly influencing the sales in Japan of Lockheed Tristar passenger jets. Osano's conviction in the long-running case was widely interpreted here as a sharp setback in the ex-premier's own court defense and a blow to his vast political fortunes.

In handing down the decision, Judge Koichi Hanya found Osano guilty on three counts of perjury committed during 1976 hearings in the Japanese parliament. The Lockheed payoffs were brought to light in U.S. Senate subcommittee hearings in February of that year.

Prosecutors have alleged that Osano, 64, acted on then prime minister Tanaka's orders in 1972 to press officials of All Nippon Airways, Japan's largest domestic airlines, to buy the Lockheed Tristars. The judge ruled Osano lied in denying he acted in the California company's behalf. Osano owns property in Hawaii as well as a hotel chain and transport company.

Osano appeared stunned when the verdict was read. He was allowed to return home rather than proceed immediately to jail, reportedly because of his history of heart trouble. His physician also was in court.

In 1947, Osano was convicted by a U.S. occupation court of misappropriating American military property. His lawyers said he will appeal the latest conviction.

Earlier today, the same court gave Tsuneo Tachikawa, 44, a four-month suspended sentence for violating foreign-exchange laws, saying he received $348,000 from Lockheed. Tachikawa is a former assistant to Lockheed's alleged chief agent, Toshio Kodama, 70, a right-wing political figure who is also on trial.

Tanaka's trial began in January 1977 and is likely to run for many more months. He has denied that he used his office to promote the aircraft sales or that he accepted money for his alleged efforts.

But observers said today's verdict against Osano, the first court ruling involving a major figure in the Lockheed case, brought prosecutors one step closer to establishing a link between the tycoon and the ex-premier.

After coming to office in 1972, Tanaka was forced to resign two years later in the wake of a blistering expose in the Japanese press, alleging that he had used political funds to enhance his private finances.

In July 1976 he was arrested on charges that he had accepted 500 million yen ($1.4 million) from Marubeni, the Japanese trading company that acted as Lockheed's agent in promoting aircraft sales here.

The storm of controversy swirling around Tanaka appeared to do little if any damage to his political power. At 63, he is still the dominant figure among ruling Liberal Democrats even though he was forced to give up party membership in disgrace following his indictment.

With at least 107 members, the faction of Liberal Democrats that bears Tanaka's name is by far the largest in parliament and gives the ex-premier power behind the scenes in party politics and the country's legislative affairs.

It is widely believed among political analysts here that Tanaka, confident of an acquittal, has been maneuvering through his loyal lieutenants to regain his old office once Prime Minister Zenko Suzuki steps down. But those efforts, sources here said, have suffered a serious setback as the result of the Osano conviction.

The sharpest jolt to Tanaka's court defense -- and his political ambitions -- came last week, however, when prosecutors called a surprise witness. Mieko Enomoto, 33, testified that her ex-husband, Toshio, Tanaka's former personal secretary, told her he had accepted the Lockheed payoff on behalf of Tanaka from a Marubeni official.

Throughout the trial, codefendant Toshio Enomoto has denied prosecutors' claims that he accepted the money. Tanaka's team of high-powered defense attorneys have mustered a battery of witnesses in a bid to prove that Enomoto was otherwise engaged when the payments allegedly were made. Mrs. Enomoto's testimony represented the first serious counter to that defense.

Tanaka's lawyers have indicated that should the verdict -- not expected for at least another year -- go against them, they plan to stage a lengthy appeal. But the recent adverse twists in Tanaka's defense have prompted Liberal Democrats to begin thinking about the unthinkable and could, political analysts said, touch off a grab for party power among Liberal Democrats.

"Until now, politicians haven't been able to imagine that a man like Tanaka might actually be convicted," said Takashi Tachibana, the writer who first exposed Tanaka's financial dealings eight years ago, "because there has never been a case like it in Japanese history. But now they find they have to start thinking about it."