CAPE TOWN, SOUTH AFRICA, JUNE 10 -- President Pieter W. Botha tonight extended South Africa's year-old state of emergency for a second year, warning that a revolutionary climate still exists in the nation despite a decline in political violence in the past year.

In an address to a joint session of Parliament here, Botha acknowledged that sweeping emergency regulations represent an infringement on the civil liberties of all South Africans. But, he said, strict security action "strengthens the basis on which the search for a peaceful political solution can take place."

Violence planned by "terrorists and their fellow travelers," the president vowed, will never be tolerated in South Africa.

The announcement was condemned immediately by leading antiapartheid campaigners, who pledged to continue opposing the government.

"We are not scared. They know they can arrest us, but in the end they will be like Hitler, who bit the dust," said Anglican Archbishop Desmond Tutu, winner of the 1984 Nobel peace prize.

The current emergency, which was imposed last June 12 in the midst of a growing rebellion in black townships against minority white rule, expires at midnight Thursday.

More than 2,500 people have died as a result of political violence since 1984, but a sharp decline in deaths attributed to racial unrest in recent months has led to demands by apartheid opponents that the emergency be lifted.

Botha, however, rejected that position in his speech to Parliament and in a subsequent, televised address to the nation.

"On June 12 last year, here in Parliament, I referred to the background against which deeds of violence and unrest were being planned and executed. According to information provided to me, I am of the opinion that this background still exists," Botha said.

Botha singled out African National Congress guerrillas based in neighboring Mozambique as playing "a cardinal role in the underground terror network" operating in South Africa.

"We will fight them, for the simple reason that they are part and parcel of the terrorist curse besetting the world today. . . . You cannot talk with the ANC without talking to its present leaders, {and} we reject them for their philosophy of violence and terror," the president said.

The current emergency -- during which an estimated total of 30,000 persons have been detained at various times without charge -- was imposed three months after Botha had lifted an emergency decree declared in 1985 in three major urban areas of South Africa.

The emergency banned all unauthorized meetings and gave sweeping powers to police to arrest suspected "subversives," make warrantless searches and detain antigovernment activists indefinitely without bringing charges. It also led to the most severe press restrictions in the world among nations purporting to maintain a democratic government.

Technically, all prisoners detained under the emergency must be ordered released at midnight Thursday. Under the new proclamation, however, they will continue to be held.

"Considering the safety of the public and the maintenance of public order, I have decided to proclaim a state of emergency once more in the whole of the republic," Botha declared to a silent Parliament, which is dominated by his ruling National Party.

Botha said that despite a dramatic drop in political violence in recent months, "information indicates that the Republic of South Africa remains a target area" of revolutionaries.

The state Bureau for Information said in a statement, "Despite the marked decrease in the number of unrest-related incidents and deaths, the underlying revolutionary climate in many parts of the country has not abated.

"It is the opinion of the South African authorities that lifting the state of emergency under the present circumstances would quickly result in a renewed cycle of violence and unrest. Radical organizations are still doing everything in their power to politicize, mobilize and intimidate the masses in their attempts to achieve their revolutionary objects," the bureau declared.