President Idi Amin of Uganda today defended himself, his regime and his country, asserting that Uganda is peaceful, prosperous and governed according to law.

In a press conference at the Afro-Arab summit meeting, Amin was by turns somber and jovial as he ranged for an hour over topics as from the controversial death of the country's Anglican archibishop to the abundance of zebras and giraffes in Uganda's national parks.

More than a hundred journalists listened to him, ignoring the speaker then addressing the summit conference, President Hafez Assad of Syria, normally a big attraction himself.

As Amin spoke, Ugandan officials handed out copies of a book, published by the Ministry of Information, that Amin said gives conclusive evidence that the archbishop and two Cabinet ministers who died with him were part of a plot by former President Milton Obote to return to power.

It contains photographs said to show chinese-made arms imported r innocent Ugandas." It also reproduces the text of what purports to be a "memorandum" to supporters in Uganda's Langi and Acholi tribes out-lining a scheme to overthrow Amin. The late archbishop, Janai Luwum, is named as a sympathizer with the alleged plot.

Amin has been accused of carrying out massacres among these two tribes and arranging the murder of the archbishop and the Cabinet ministers. The official explanation of their deaths is that they were killed in an auto accident while trying to over-power the army officer who was taking them to be interrogated. The book contains what are said to be autopsy reports from a Kampala hospital saying they died of skull fractures and internal injuries, not bullet wounds.

[The alleged purge of the two tribes appears to be easing after Amin crushed underground opposition to his regime and crippled the church, diplomatic sources in Nairobi, Kenya, said, according to United Press International. The sources said Amin would not have left Uganda to attend the Cairo summit if there had been any signs of continuing resistance or threat to him.]

"We have the rule of law," Amin said. "Anybody who commits a crime is tried according to the law."

He said 16 persons are in jail awaiting trial on charges of complicity in the plot and "the Ugandan masses wanted them executed immediately" but he insisted that they be tried.

Amin dwelled at length on some of his favorite themes. He said the imperialists. Zionists, Americans, British, Kenyans and Tanzanians are trying to overthrow him. He said he is the "only African" strong enough to challenge these forces.

Amin denied reports that there are Cuban military advisers in Uganda. "We have excellent relations with Cuba but at the moment we don't have Cuban military advisers," he said.

He angrily rebuffed a suggestion that an international commission of inquiry be allowed into Uganda to investigate reports of atrocities there.

"Thousands of people are dying in New York, in Washington, in all parts of the United States everyday in traffic accidents," Amin said. "We should send an independent committee of inquiry to America to investigate the martyring of your own president, President John F. Kennedy."

In the United States, Amin said, "They killed the red Indians. They are not ashamed of killing and butchering millions in Hiroshima. Vietnam and now they are talking about Amin. Well, Amin is never afraid or a coward. The Zionists want to kill me."

Amin said it is "not necessary to send anybody" to investigate alleged atrocities in Uganda. "If somebody dies in an accident, that's an affair for our police.

As for the British, he said, "how many Northern Irish have they killed? How many Catholics? They are discriminating against their own people. I am a Moslem but the majority of my government are Christian," an allusion to charges that he is persecuting Uganda's Christian majority.

Any reports of hunger, poverty, unrest or atrocities in Uganda, he said, are "nonsense" being spread by "exiles. Exiles will never speak good about their country." To ascertain the truth, he said, the press should go see Uganda themselves. "Uganda is open to all the world," he said.

In rambling references to the U. S. Central Intelligence Agency, Amin said. "There are many Americans who are my friends who pass me information from the CIA."

"The flight engineer on my air-plane is an American," Amin said. "But the Americans are martyring strong leaders like me," he said, adding that he is on a list to be myrtyrde by the CIA."

Asked about negative press reports about Uganda, Amin said, "I am proud when they speak about me. Any strong man must be happy. Once they begin to speak good about me, you will know that I am in the pocket of the CIA."

The burly Amin, who was introduced as "Field Marshal Doctor Idi Amin Dada, VC, DSO, MC," smiled when asked to describe his political system briefly. He replied that it was based on "whas is best for Uganda" with some elements of capitalism, some of socialism.

United Press International reported these other developments from Nairobi, Kenya:

The Nairobi newspaper Daily Nation has reported that the Soviet Union is deeply involved in the mass killing of Ugandans by Amin's security forces. These forces are being "trained and directed" by the Soviet KGB, the newspaper said.

It urged Ugandans to establish their own government-in-exile, demanded that the United Nations "disarm" Uganda and blasted Arab and African nations for their silence over events in Uganda.