The All Africa Conference of Churches called off a funeral service for the Anglican archbishop of Uganda, Janani Luwum, after it learned that Ugandan authorities had buried his body without returning it to the archbishop's family.

Christian leaders from all over Africa had planned to attend today's funeral service at St. Paul's Cathedral in the Uganda capital of Kampala, if they could get across the Uganda border.

"I do now know what the truth is, but one thing is now certain - he was not killed in any car accident," Canon Burgess Carr, secretary general of the All Africa Conference of Churches, said here in reference to the offical Ugandan version of the archbishop's death.

Carr said he would fly to Washington next week and hoped to discuss the situation in Uganda with President Carter. There have been reports that hundreds of Christians have been slain by Amin's forces. Carr said Luwum's widow was isolated in her house and feared for her life.

In London, the Observer newspaper reported that members of Uganda's State Research Department, which is personally controlled by Amin, shot and killed Archbishop Luwum shortly after he was arrested along with two Cabinet ministers earlier this week and then burned his body. The report, quoting "sources in Kampala and informed intelligence sources" in Nairobi, Kenya, said the ministers also were shot and killed.