In a bid to end continuing racial unrest, the South African government today banned the country's major black political movement, the United Democratic Front, and 28 allied organizations from holding meetings in many areas for the next three months.

A proclamation issued by the minister of law and order, Louis le Grange, also made it a crime for anyone to encourage protest strikes or school boycotts, strategies employed by black activists starting seven months ago with the intensified campaigning against the segregationist system.

At the same time, 24 members of the Democratic Front were reportedly detained by security police in the Ciskei tribal "homeland" in troubled eastern Cape Province.

The crackdown on the front and its allies is assumed to be the action President Pieter W. Botha warned of when he told a specially convened joint sitting of the racially segmented Parliament Wednesday that he had given orders for "appropriate steps" to be taken to end the unrest.

In another development today, a trial date of May 20 was set for 16 leaders of the Democratic Front facing allegations of high treason.

Meanwhile, more contradictions in the official version of last week's police shooting of 19 blacks near the eastern Cape Province town of Uitenhage emerged at the hearings of a commission of inquiry.

Although civil rights organizations condemned the ban on meetings, warning that it was likely to increase rather than stop the unrest, the action was less severe than many observers had predicted after Botha made his announcement. Some thought he was getting ready to outlaw the Democratic Front altogether.

[In Washington, State Department deputy spokesman Edward Djerejian said, "We continue to believe that measures aimed at silencing legitimate and peaceful opposition to apartheid are not conducive to finding a solution to the country's major problem."]

The ban applies particularly to the eastern Cape Province, where the worst unrest has occurred in recent weeks. Some organizations in townships to the east of Johannesburg, where there has been persistent unrest, also have been prohibited from holding meetings.

Sheena Duncan, president of the respected Black Sash organization which keeps in close touch with the black townships, was among those sharply critical of the meeting ban, describing it as "an utterly stupid" way to try to stop the violence. She predicted it would lead to increased clashes between blacks and police.

Allan Boesak, patron of the Democratic Front, also predicted that the meeting ban would "exacerbate an already volatile situation."

"If people cannot meet to voice their protest, the government will drive them to other measures in order to express their feelings," Boesak said.

The general secretary of the South African Council of Churches, C.F. Beyers Naude, called the banning "an act of desperation" aimed at trying to "stem the tide of liberation."

"We believe that this act can only lead to further tension and polarization because it does not address itself to the real problems or their solution," Naude said.

A large crowd, many wearing the green, yellow and black colors of the outlawed African National Congress, gathered at the court in Durban today when eight of the 16 Democratic Front leaders accused of high treason made a formal appearance.

According to news agency reports, the eight, including one of the front's three copresidents, Albertina Sisulu, stood in silence for a minute before the hearing began to honor the 19 blacks killed at Uitenhage.

Although some of the prisoners have been in custody more than three months, provincial attorney general W.C. Gey van Pittius said today he still was not able to present an indictment. The government has issued an order under the security laws prohibiting any magistrate or judge from granting bail.

In Uitenhage, the commission of inquiry into the shooting of the 19 blacks revealed further contradictions in the official version of what happened.

Le Grange told Parliament after the shooting that the police had been compelled to open fire to protect themselves from a mob that attacked them with sticks, stones and gasoline bombs, but the second in command of the police contingent, Warrant Officer Jacobus W. Pentz, told the inquiry today that he had not seen any gasoline bombs being thrown.

Pentz admitted that without the threat of gasoline bombs the police were virtually impregnable inside their big Casspir armored personnel carrier, news agencies reported.

The officer also said under cross-examination that he could not explain why a piece of iron, a piece of wood and a pickax handle were the only weapons found at the scene after the shooting, nor why a police photograph showed no stones there.

Pentz told the commission, presided over by Judge Donald D. Kannemeyer, that four police Casspirs were on their way to the scene of the shooting, whereas le Grange told Parliament only one was there.

He added that the police who went to the black township of Langa, near Uitenhage, on March 21 were not issued tear gas, rubber bullets or loud speakers.

They had only semiautomatic assault rifles, pistols and shotguns with heavier-than-usual cartridges, Pentz said.

The commander of the police contingent, Lt. John W. Fouche, 43, said he had faced a "violently unruly" crowd that was "clearly . . . on their way to the city center."

Fouche said he ordered the crowd to disperse because their gathering was illegal. When they continued to advance he fired a warning shot into the road next to the leader.

"The leader sprang about even more and pulled out a bottle and a book from his jacket. A Colored [mixed race] woman jumped out from the side of the road . . . . She jumped in the air and threw stones at Pentz's Casspir. I realized there was trouble and immediately gave the order to the men to fire," Fouche said.

Sporadic unrest continued in black areas of the eastern Cape yesterday, and the unrest flickered into Natal Province for the first time when police used tear gas to disperse a crowd of 200 in Lamontville township near Durban.