Racial violence erupted in the center of a major South African city for the second time in a week when police clashed with demonstrators in Cape Town today.

The violence in central Cape Town followed rioting in downtown Johannesburg last Friday, when blacks rampaged through six city blocks clashing with whites and smashing shop windows after a memorial service for a supporter of the black underground who was hanged for killing a policeman.

Even as the confrontation in Cape Town was escalating, President Pieter W. Botha announced a lifting of emergency regulations in six of the 36 towns and cities where they were imposed three months ago, saying the stringent measures had proved effective in restoring order in the troubled areas.

The violence in and around Cape Town, where black activists yesterday threw two hand grenades and fired two shots at security force vehicles, and unrest in other parts of the country that included the death of a black youth in the eastern Cape Province town of Cradock today did not seem to bear out Botha's claim that the emergency was proving effective in "ensuring a return to stability."

Observers noted that the six towns where the emergency regulations have been lifted, four in the eastern Cape Province and two in Transvaal, are all on the periphery of the main unrest areas.

Two more blacks were killed in clashes with police in the Crossroads squatter camp outside Cape Town today, bringing the death toll in that region during the past two months to 63 and the total killed in South Africa since racial violence began in September last year to nearly 800.

Young blacks hurled rocks and gasoline bombs at automobiles driving along a major highway to Cape Town airport for the third consecutive day, and police advised motorists in that city to wear crash helmets for protection.

Injuries in today's violence in Cape Town were minor as police used a water cannon and horsewhips to disperse a large crowd of black and mixed-race demonstrators who gathered in the city's main thoroughfare, Adderley Street.

Whites and blacks scattered as police in riot helmets lashed at them with horsewhips, knocking some down, and a water cannon fired purple dye at the crowd, staining buildings and splashing into some stores.

Shops closed their doors, some locking in customers, and several pulled down their protective metal screens as the clash continued for more than an hour. Flower sellers at a large Adderley Street stall fled, abandoning their wares. While police sealed off central city streets to traffic, an officer with a bullhorn ordered store employes to return to their shops and other people to leave the area.

"All people who don't work here, move," he ordered, adding that "this is valid for whites as well."

According to news agency reports, today's police action began when a busload of black women arrived in Adderley Street to stage a demonstration demanding the withdrawal of troops from the segregated black and mixed-race townships outside Cape Town, where there have been violent clashes between local inhabitants and the security forces during the past two months.

A second crowd of blacks gathered at the same time outside a nearby courthouse, where three mixed-race men were being tried on a charge of murdering a policeman during a funeral rally last March.

Showing hesitancy in the face of the large number of whites in the crowd, officers pleaded with the crowd to disperse before giving the order in Afrikaans to maak skoon, or "clean up."

"You are going to give me laryngitis, my throat won't take it -- please, people, disperse, otherwise we will have to take action," an officer begged at one point.

The assessment of most observers here is that the overall level of racial violence in the country has increased since the partial state of emergency was declared July 20.

The violence has tended to shift to new areas, such as Cape Town, Natal and the northeastern Cape Province, while continuing to simmer in most of the areas where it originally erupted.

[A bomb exploded late Thursday night near Durban at a school to be used for voting in a white parliamentary election, killing two blacks who apparently had just planted the device, the Associated Press reported.]

Overall, the daily casualty rate has more than doubled and the level of black anger appears to have intensified.

Fourteen news reporters, including four foreign television cameramen, were arrested and four others said they were assaulted by police during the unrest in Cape Town and its adjoining townships today, according to news agency reports.

The foreign cameramen were held in a police truck, then taken to a police station for questioning. They were later released without charges, as were the other reporters.

The reporters who said they were assaulted said police hit them with horsewhips while dispersing the crowd in downtown Cape Town. One foreign cameraman said he was filming automobiles being overturned in the city center when an officer grabbed him by the throat, then ordered a subordinate to "take him away."