The prodecessor of the Anglican archbishop who died last week in Uganda said yesterday he has evidence that the archbishop. Janani Luwum, was shot to death, not killed in an automobile crash as Ugandan President Idi Amin has said.

The Rt. Rev. Leslie Brown, now bishop of St. Edmundsbury in Ipswich, England, said he spoke to someone "absolutely reliable" who had seen the archibishop's body. It had two bullet wounds in the chest and one in the mouth, Bishop Brown said.

Brown, who attended a memorial service for Archbishop Luwum in Kenya, said he had also heard that Christians were being persecuted in Uganda.

"I would never have believed this before," he said, "but I was told that prominent Christians in towns and villages were being picked up and were disappearing."

Meanwhile, Amin charged that the archbishop of Canterbury was involved in a "sinister plan to cause chaos" in Uganda.

In a message to the Organization of African Unity, broadcast on Radio Uganda, Amin named Donald Coggan, the archbishop of Canterbury, and Canon Burgess Carr, secretary of the All-African Conference of Churches, as conspirators. Amin denounced Carr as a "microphone for Zionism." Carr and other church leaders have blamed Amin for Luwum's death.

Amin's message said he would welcome a delegation from any government to investigate the situation in Uganda. He said the country was calm after surviving a "dangerous situation" during which armed raiders entered the country.

The deaths of Archbishop Luwum and two Cabinet ministers sparked an international outery against Amin, who has been accused of murdering thousands of Ugandans since he seized power six years ago.

Britain, Canada, Australia and other governments have called for a highlevel international investigation of the situation in Uganda.

Amin has steadfastly insisted that the archbishop and Cabinet ministers Erinayo Oryema and Charles ObothOfumbi were killed in a car crash as divine retribution for their plot against him.

Meanwhile, the Tanzanian government newspaper, the Daily News, said Amin personally shot Archbishop Luwum during a torture session.

Tanzania's President Julius Nyerere and Amin have been enemies for years, and the Tanzanian press often criticizes the Ugandan leader.

The Daily News story, attributed to "reliable sources," said soldiers stripped the archbishop and whipped him in front of Amin and his aides at the Ugandan president's Nakasero Lodge.

It said the beating was interrupted for 30 minutes so that everyone could listen to British Broadcasting Corp.'s evening news report and "Focus on Africa" program.

The newspaper article said the archbishop's prayers and denials of guilt enraged Amin, who beat Luwum and shouted that "God had empowered him to give the archbishop and other church leaders the last warning."

After the break for news, the article said, there "followed very bizarre, sacrilegious and obscene activities, during which Amin pulled out his pistol and shot the archbishop twice on the left side of the chest." It said he died instantly.

Ugandan telephone and telex communications, cut since Saturday, were restored yesterday. The cutoff of communications had raised new fears of attacks on the country's more than 5 million Christians.

Amin, who is a Moslem, has often accused Christians of trying to undermine his government.

In London, the archbishop of Canterbury said Amin should not be allowed to enter Britain, and added that he had never doubted that Luwum was murdered.

"My personal feelings are that he should not be allowed in," Coggan said. "The church throughout the world is indignant at the atrocities which have been happening recently and in the past. We must bring all possible pressure to bear to condemn the atrocities."

Canon Carr said the first step toward diplomatic isolation of Amin should be a boycott of this week's meeting in Uganda of African, Caribbean and Pacific countries trying to develop closer ties with the European Economic Community. Uganda Radio said 11 delegations already had arrived and more were en route.