Ugandan President Idi Amin has told a Canadian journalist that Anglican Archbishop Janani Luwum, who was killed in Uganda in February, had been arrested because he had been smuggling weapons into the country.

Amin had charged previously that Luwum had masterminded an attempted coup against the Amin government. The smuggling charge appeared today in copyrighted stories written by reporter Gerald Utting for the Toronto Star.

Utting said Amin reiterated - in five hours of interviews granted after Utting's release from a Ugandan prison - that Luwum, the primate of Uganda, was killed in atraffic accident while in custody. Amin's opponents have charged that he was murdered.

Utting's meeting with Amin took place Sunday at a resort on Lake Victoria near Kampala, the Ugandan capital. The two men drank and dined, watched a group of costumed girls perform traditional dances, and conversed in a small room where two masseuses oiled and massaged Amin's huge body.

At one point Amin jumped off the massage table, took a cassette player from an attache case, and turned on the bagpipe and drum music of a British Highland regiment.

Amin boasted of his popularity with other African leaders.At the recent conference of the Organization of African Unity in Libreville, Gabon, he said, people who had condemned him at last month's Commonwealth conference in London "came up and shook my hand. "

He told Utting that he believes the UNITA movement in angola, "supported by the United States and South Africa," is gaining ground against the governing Marxist Popular Movement for the Liberation of Angola.

During the Angolan civil war, he said, UNITA was "winning until the Cubans invaded Angola." He said UNITA forces are learning how to fight the Cubans by outflanking them and avoiding their firepower.

Utting said Amin also told him that British Prime Minister James Callaghan kept him away from the Commonwealth conference because "they are afraid of me." He added: "I am very frank. They want only the tame Commonwealth leaders. But I dominated the British newspapers during the queen's jubilee."

He said he plans to visit Cuba this month or next to see "my best friend Fidel Castro" and hopes to go to other Latin American countries as well.

Utting reported that when he questioned Amin about the 1976 raid in which Israeli forces freed hostages held captive at Uganda's Entebbe Airport by Palestinian terrorists, Amin told him:

Moshe Dayan (Israeli foreign minister and former defense minister) is my best friend. He gave us tanks . . . but then Israel killed my soldiers at Entebbe when all we were trying to do was insure the safety of the passengers hijacked by the Palestinians."

Utting's account of the interview was written in London, where he flew after nearly three weks of confinement in Uganda.

He said Amin told him he was looking better than when he was arrested, and he replied that he had lost "about 20 pounds of fat."

"Your wife will thank me for it," Amin replied.

"I have one big message for the Canadian people," Amin told Utting. "I believe that 40 per cent of your country is owned by the Americans and you must try to end this. You must fight against more economic domination."