JOHANNESBURG, JUNE 8 -- Human rights advocates today generally welcomed President Frederik W. de Klerk's decision to lift a four-year-old state of emergency in much of South Africa, but said security laws still in force will leave the government with many of the same powers it had under the emergency decree.

De Klerk, in a move that had been demanded by black nationalist groups as a condition for negotiations on the country's political future, announced Thursday that he was lifting the state of emergency as of 12 a.m. Saturday in three of South Africa's four provinces. It will remain in force in war-torn Natal, he said, because of persistent violence there.

Government critics, including the African National Congress, the largest black nationalist organization, condemned de Klerk's decision to retain the emergency in Natal, where hundreds of people have been killed in fighting this year between rival black organizations. Some pointed out that the emergency had failed to prevent violence there, and said the lifting of the emergency decree would prove to be a stabilizing move.

But the far-right Conservative Party, which opposes de Klerk's reforms, said the lifting of the emergency would lead to chaos. The Conservatives made substantial gains Wednesday in a special parliamentary election in Natal province, coming within 550 votes of winning a hitherto safe government seat.

According to the human rights sources, the lifting of the state of emergency means that police will no longer be able to arrest protesters or activists en masse. In addition, the authority to detain suspects has been taken away from lower-ranking police officers, who have lost their immunity from prosecution for human rights abuses.

But, the sources said, the Internal Security Act still allows for the arrest and unlimited detention of people as well as the banning of anti-apartheid protests at the whim of police.

"It has to be welcomed," Ahmed Motala, director of litigations for the Lawyers for Human Rights organization, said of de Klerk's decision. "It's positive." But he warned that "the government still has a whole arsenal of security legislation."

Max Coleman, a leader of the Human Rights Commission, said the powers available to the government under the Internal Security Act make it possible for the police to take most of the same actions and impose most of the same restrictions as those provided for by the stage of emergency decree.

"The people I have contacted in the {black} townships say it will make very little difference on the ground," said Coleman, whose commission monitors arrests, detentions and other repressive government activities.

Even the cautious Business Day newspaper noted that "permanent laws that remain in place still allow the government to outlaw any organization, ban any publication or place any person under house arrest."

Perhaps the most hated piece of security legislation among black activists and human rights advocates here is Section 29 of the Internal Security Act, which allows police to detain a suspect and hold that person incommunicado -- even from a lawyer -- for an indefinite period of time.

That section was used in the case of Horatio Motjuwadi, sports editor of the black-oriented daily, the Sowetan, who was picked up by the police April 11 and held 42 days without being charged or allowed to see a lawyer. He was released after being taken to a hospital for treatment of an illness.

"It's the worst law in the country and it's still on the books," said Joe Tloloe, a senior Sowetan editor. "On the whole only the person being held and the police know what's happening."

Coleman noted that Section 46 of the Internal Security Act, which requires groups to apply for a permit to hold a march or rally from the Ministry of Law and Order or a magistrate, was renewed March 30 as was required to keep it in effect.

Many anti-apartheid groups, particularly the African National Congress, are now routinely being granted permission to hold mass demonstrations in some areas. But in the country's smaller towns and cities, particularly those where the Conservative Party dominates, permission is routinely refused.

"The freedom of assembly doesn't exist," said Coleman.

Coleman said the main benefit to anti-apartheid activists from the lifting of the state of emergency will be an end to mass arrests, such as the one that occurred immediately after the emergency was first imposed on June 12, 1986. He said the police then arrested 10,000 people in three weeks.

"You couldn't do that under the Internal Security Act," he said.

But Coleman warned that restrictions under the Internal Security Act still allow the government to ban any South African publication from quoting by name some 300 anti-apartheid activists on the so-called Consolidated List. About 200 names have been taken off the list since de Klerk lifted a ban on all anti-apartheid groups in February.

Coleman also said trials involving persons alleged to have committed politically related offenses are continuing at a rapid pace. His group counted 400 such trials last year and the rate is about the same this year, he said.

The Human Rights Commission estimates there are 3,000 people in jail for so-called political offenses, 80 of them on death row. In February, de Klerk suspended further executions pending new legislation.