A black South African labor union charged today that a senior member died of head injuries after being beaten by police who arrested him Saturday. The unionist died yesterday.

The Chemical Workers' Industrial Union stopped short of openly accusing the police of killing shop steward Andries Raditsela, 29, but its account of events leading up to his death implied it. Union lawyers said they were considering placement of charges against the police.

Police headquarters in Pretoria said it could make no comment because Raditsela's death was the subject of an official investigation.

The union's charge is made against a backdrop of continuing racial unrest in which the police and black activists daily accuse each other of wanton violence.

The accusation that Raditsela was fatally injured while under arrest is likely to revive periodic accusations of brutal treatment made against South African police.

The general secretary of the chemical union, Rod Crompton, said today that Raditsela was walking with friends towards a rental car in Tsakane black township, east of Johannesburg, when police patrolling in an armored vehicle stopped to question him.

The police thought the car had been stolen, Crompton said. He added that while Raditsela was showing them documentation from the car-rental company, another police vehicle pulled up and a white officer in riot gear walked up to the unionist and struck him in the face.

Raditsela was dragged to one of the police vehicles and driven away, the union secretary went on. After some hours his parents found him, still in police custody, lying unconscious on the veranda of a government building in the township.

Later he regained consciousness, Crompton said, but was disoriented, his movements were impaired and he could not speak properly. Raditsela was taken to a hospital, where colleagues found him unconscious yesterday morning. He died in the afternoon.