JOHANNESBURG, South Africa (AP) _ Police arrested two suspected ANC militants and a third man Sunday for the murder of a farmer who allegedly had information about army plots to kill black activists.

Andre de Villiers, who was white, was shot to death on his farm Monday. The African National Congress said de Villiers, 42, was killed shortly before he was to provide the ANC with details about alleged death plots.

The ANC and other opposition groups have repeatedly charged government security forces have killed and assaulted anti-apartheid activists and continue to foment political violence. The government, which is seeking talks to end apartheid, denies the charges.

De Villiers' friends and family disputed police reports the motive was robbery, saying nothing was taken from the home.

Police Maj.-Gen. Koos Calitz, who is heading the investigation, said three men - two of them alleged members of the ANC's military wing - were arrested in connection with the slaying.

Police did not immediately identify the men arrested. Calitz said he expected more arrests.

The ANC denounced Calitz's statement, saying it ''confirms our worst fears about the propagandistic role played by the police force.'' It said it would investigate the allegations.

Law and Order Minister Hernus Kriel had offered a reward of $18,500 for information leading to de Villiers' killers, and the liberal Democratic Party demanded an investigation of his death.

The ANC and friends of de Villiers said he gained information about alleged death squads when a secret army unit, known as ''Hammer,'' used his former business as a base. They denied he was a member of the ANC or any other political group.

Local media reports recently have linked the army unit to the 1985 killings of black activist Matthew Goniwe and others.

The ANC said de Villiers approached the group about three months ago and had given it some information, but it has not released details. It said he called the ANC a few hours before his death and promised more information.

Also Sunday, a newspaper reported that an electronics agency investigating the erasure of police tapes during a township massacre June 17 had been dropped because of ties with the government.

The Goldstone Commission, a judicial panel investigating the massacre, asked the Grinaker Electronic Agency earlier this month to study the tapes after police said they had been erased accidentally.

The Sunday Times said Grinaker was a major defense force contractor and had received at least five government grants in the past two years. The commission, chairman said agency would no longer be used in the massacre probe, the Times said.

At least 42 blacks were killed in the massacre in the township of Boipatong. The ANC and some township residents have said police ignored calls for help and even helped the attackers.