Two government doctors who treated black activist Steve Biko before his death in police custody eight years ago were found guilty today of serious misconduct. They were not barred from practicing medicine, however.

The South African Medical and Dental Council's disciplinary committee found that the two physicians, both white, had failed to provide adequate care for Biko, who died on the floor of a prison cell here Sept. 12, 1977, from brain and internal injuries. An inquest had concluded earlier that he suffered the injuries during police interrogation on security charges.

Biko, 30, was the spokesman of the black consciousness movement and was seen as a potential national leader. His death provoked international outrage over apartheid, South Africa's system of racial separation, and made him a martyr in the fight against white-minority rule.

One of the doctors, Benjamin Tucker, the chief district surgeon for Port Elizabeth at the time of Biko's death, was found guilty of 10 counts of disgraceful professional conduct in failing to examine Biko properly and in allowing the security police to move him, lying naked in the back of police van and without a medical attendant, 750 miles by road from Port Elizabeth to a prison hospital in Pretoria.

The other doctor, Ivor Lang, a district surgeon in Port Elizabeth, was found guilty of eight counts of improper conduct for failing to notice a wound on Biko's forehead and for failing to keep proper medical records on Biko. Lang had given the police a medical certificate saying that he could find no symptoms of injury or illness or evidence of other abnormality on the first day he saw Biko, who was manacled to a grill in a police station.

Both men were absolved, however, of subordinating Biko's interests to those of the security police, the panel's chairman said, because of their "understanding of security procedures existing at the time."

Tucker, 64, was suspended from medical practice for three months, but that was suspended for two years. Lang, 60, was reprimanded formally by the disciplinary committee. Both could have been barred permanently from medical practice.

Biko's widow, Nontsikelelo, a nurse in King William's Town, near Port Elizabeth, said that she was "happy the truth has at last come out," but added that she had expected the sentences to be heavier.

The Azanian People's Organization, the principal black consciousness group today, described the medical council's decision as tokenism by a "body that has consistently shown hostility towards doctors with a social conscience and has dragged its feet in trying the notorious Biko doctors."

Biko, a former medical student, had espoused the philosophy that blacks cannot depend on whites to help overturn white-minority rule in South Africa. His slogan was, "Black man, you are on your own," and black consciousness groups still maintain that this is the only route toward ending apartheid.