PRETORIA, South Africa (AP) _ President P.W. Botha said today his government would prefer economic sanctions to ''national suicide'' and said he had rejected the British foreign secretary's plea for unconditional release of Nelson Mandela.

''I hope this hysterical outcry of certain Western countries against South Africa will soon pass,'' he said.

''I don't believe in sanctions. ... But if we are forced until our backs are against the wall, we will have no alternative but to stand up in self- respect and say to the world: 'You won't force South Africans to commit national suicide.'''

Botha, who spoke with reporters after meeting with Sir Geoffrey Howe, said he told the British foreign secretary that Mandela would remain jailed and the African National Congress he leads would remain outlawed until it renounces violence and removes communist leaders from the ANC.

Mandela, an ANC leader, has been in prison since 1964 serving a life sentence on charges of plotting against the South African government. The ANC, originally a civil rights group, began a campaign of sabotage in 1960.

In a separate news conference at the end of his weeklong peace mission to southern Africa, Howe said peaceful dialogue was not possible unless Mandela and the ANC could participate freely.

''The responses I've received have not yet enabled me to proclaim that I have made the progress I would have liked,'' Howe said.

The only new South African proposal referred to by Botha was an offer to meet with leaders from Western Europe and southern African countries to discuss ''the problems that afflict us and others in the region.''

Meanwhile, a court has ruled that divisional police commissioners cannot ban meetings under South Africa's state of emergency, possibly invalidating more than 20 such orders nationwide.

The Monday ruling by Transvaal Province Supreme Court came in a case brought by the United Democratic Front, the nation's largest anti-apartheid organization. The suit challenged a July 10 order of the Soweto police commissioner prohibiting gatherings by the UDF and 25 other groups under the six-week-old state of emergency.

The court held that Botha could delegate authority to the police commissioner to issue orders under the emergency, but that the commissioner could not pass on the powers to lower-ranking officials.

Howe's visit to South Africa was on behalf of the European Common Market, which is preparing to consider economic sanctions against South Africa to protest its continued apartheid policy of racial separation.

Howe said that while he had put forward the Common Market's position, ''I don't want to raise any false hopes, I've made very clear the scale of the leap that has to be made. It hasn't yet been made.''

Howe said the decision to open dialogue had to be made by the South African government.

''The blunt truth is that sooner or later all the people of South Africa will have to get round the negotiating table. It is plain common sense that it should be sooner.''

Howe's findings are expected to have a major effect on British policy toward its South African investments. Britain's Prime Minister Margaret Thatcher and President Reagan oppose economic sanctions as a means to end apartheid.

Most South African black activists have avoided Howe and have described his tour as an attempt to delay Western decisions on whether to impose sanctions.

Howe has visited the neighboring black-ruled nations of Zambia, Botswana, Swaziland and Lesotho and talked with their leaders.

The death toll from incidents of unrest during the emergency rose to 193, with the government information bureau reporting five more deaths in the previous 24 hours. It said two people were killed by security force patrols firing on groups which attacked them, and three blacks were burned to death by other blacks.

The bureau also reported that a landmine exploded under a security force vehicle today without causing injury in Kayanansane township near Nelspruit, in eastern Transvaal province.

More than 2,000 people, nearly all of them black, have been killed since the uprising against apartheid intensified in September 1984.

Under the state of emergency decree, journalists are prohibited from reporting the actions of security forces without official permission, publishing ''subversive statements'' or identifying any of the thousands of people detained without charge.

Since the president declared the emergency on June 12, a score of divisional police commissioners have banned gatherings of political organizations, prohibited student meetings at schools, and restricted funerals.

The Monday court ruling technically applies only to Transvaal, but is considered valid countrywide unless another provincial court rules differently. The court ordered the government to reimburse the United Democratic Front for the costs of the suit.

Attorney Dallah Lamar said the anti-apartheid group would file a similar challenge in Cape province Supreme Court on Friday.