JOHANNESBURG, South Africa (AP) _ A white policeman killed a black youth execution-style during a foray into a black township that followed heavy drinking and a blood-brother ritual, two white officers testified.

Constable Michael Neveling, testifying Tuesday in the eastern Cape Province town of Graaff-Reinet, said the ritual was conducted so the unit's 10 members would keep secrets and protect one another.

But Neveling and another unit member, Sgt. Heinrich Bloementhal, have testified over the past 10 days that, after initially participating in a cover-up, they decided to tell the truth about ther squad's actions in the black township of Craddock on July 26, 1986.

They have been testifying against the squad leader, Warrant Officer Leon De Villiers, 36, and Constable David Goosen, 26, who are charged with two counts of murder, two of assault and one of attempting to defeat the ends of justice. Conviction on the murder charges could carry the death penalty.

The defendants, who have pleaded innocent to all charges, are the only members of the unit to be prosecuted.

Neveling said the alleged killings and assaults occurred after the squad learned that a police vehicle had been stoned in Craddock. They then decided to conduct a pre-dawn patrol in the town.

Neveling said the operation was ''unofficial'' because the officers lacked permission and were drunk.

He said the officers cut their forearms with a knife and pressed their arms together so the blood would mingle. They then armed themselves with weapons including knives, a shovel and an ax, and entered the township, Neveling said.

During the operation, Neveling said, he saw Goosen stab a black man in the chest.

The officers left the township, then were ordered back after daybreak, Neveling said.

He said four blacks were taken to a secluded spot and interrogated while officers beat them and held plastic bags over their heads.

Neveling testified that one of the blacks, 18-year-old Wheanut Stuurman, was bleeding heavily, and that De Villiers said the youth should be ''taken out'' because he was too badly hurt to be detained.

Several officers, including Goosen, took Stuurman to a canal, Neveling said.

While waiting by the police van, Neveling said he heard De Villiers say: ''I wonder why Goosen is taking so long to shoot that boy.'' Neveling said he then heard a shot.

Goosen, returning to the van, said he had shot Stuurman through the neck and thrown his body in the canal, Neveling said.

Neveling said that when a police investigation of the incident began, the members of the unit met at De Villiers' home in Port Elizabeth and decided to contend that Stuurman was killed while trying to escape after Goosen took him to the canal to rinse his face.