JOHANNESBURG, DEC. 11 -- The South African government today placed new restrictions on the recently freed chairman of the African National Congress, Govan Mbeki, confining him to his home town of Port Elizabeth and ordering him not to give press interviews or write for publication.

The government said the 77-year-old Mbeki is still committed to communism and the overthrow of white minority rule, and that the restrictions were necessary to prevent the "promotion of the revolutionary climate."

The gag order dashed hopes of many antiapartheid campaigners that ANC leader Nelson Mandela and other security prisoners would be released soon in preparation for power-sharing negotiations.

The freeing of prisoners such as Mandela and ANC leader Walter Sisulu, both of whom were sentenced with Mbeki in 1964, had been held out by black nationalists as the only way moderate black leaders could participate in power-sharing talks with Pretoria.

Mbeki, who was freed Nov. 5 after serving 23 years of a life sentence for sabotage and treason, insisted at the time that his release was unconditional. The government said, however, that as a "listed" person, he may not be quoted by domestic media.

The commissioner of the South African police, Gen. Hennie de Witt, said Mbeki had openly declared that he is still a member of the outlawed ANC and the South African Communist Party, and that he had publicly "encouraged the youth to continue with the struggle." Mbeki, de Witt added, "also indicated that the ANC was leading him in his conduct, and it is clear that his presence at gatherings is being used to provide the ANC with a platform."

Liberal opposition leaders and antiapartheid campaigners immediately condemned the government's move, warning that it would lead to renewed violence.

Anglican Archbishop Desmond Tutu said Mbeki's release had been the most hopeful sign yet that South Africa's crisis could be resolved peacefully.

By restricting him, Tutu said, the government was, in effect, "choosing a path of violent confrontation."

Mbeki's attorney, Priscilla Jana, said she was preparing to appeal the decision. She said Mbeki was "greatly disappointed and distressed" by the order because he had been informed upon his release that his movements would not be restricted. Mbeki could not be reached for comment.

Mbeki was scheduled to speak at a political rally in Cape Town on Sunday, expected to attract 50,000 persons. A local magistrate banned the rally on Tuesday without stating his reasons.

Organizers of the rally then announced Mbeki would speak at a private indoor meeting in Cape Town, attended by representatives of about 100 antiapartheid groups. The new restrictions will prevent him from attending that event.

Mbeki had been scheduled to speak at a rally in Port Elizabeth on Nov. 28, but the event was canceled after a provincial Supreme Court justice overruled a local magistrate and declared that the rally would fan the "revolutionary climate."

Antiapartheid groups condemned the decisions, saying the government had reneged on its promise of an unconditional release.

Joseph Marks, secretary of the western Cape Province branch of the United Democratic Front, a coalition of 700 antiapartheid groups, said, "Although the government released Mr. Mbeki and promised that he would be allowed to participate in legal political activities, it now seems determined to silence him."

Organizers of the Port Elizabeth and Cape Town rallies said that elaborate preparations had been made to ensure that the assemblies were peaceful. They said hundreds of marshals had been assigned to maintain discipline.

Some antiapartheid activists said they thought the restrictions on Mbeki were the result of a backlash by the far-right Conservative Party, the official opposition party in Parliament.

Jana, however, said she thought the government had miscalculated Mbeki's stature as a black leader and had been "obviously embarrassed" that it could not continue to maintain that ANC leaders do not have popular support among blacks.

She said government officials apparently had thought that Mbeki, because of his age and frail health, would retire quietly to Port Elizabeth.