In South Africa's biggest political crackdown in years, security police today arrested nearly the entire top leadership of the major black nationalist organization, the United Democratic Front.

Thirteen front leaders were taken from their homes in predawn raids in the main cities. A police spokesman, Lt. Henry Beck, said six were to be charged with high treason. The others were detained for interrogation.

The arrests appear to be in reaction to a new wave of violence in many black ghettos, which led to a bloody battle between police and demonstrators in the Crossroads settlement near Cape Town yesterday.

As violence continued in Crossroads today and spread to other black townships nearby, the casualty toll rose to nine black residents killed and 195 injured. For the second day, the police fired rubber bullets and birdshot at the crowds.

There was widespread anger among blacks at today's arrests, and some critics feared it might give another twist to the current cycle of violence as black groups organize protest demonstrations that could lead to further clashes with the police.

The six leaders arrested today who are to be charged with treason include a copresident of the democratic front, Albertina Sisulu, who is the wife of Walter Sisulu, former general secretary of the outlawed African National Congress. He has served 20 years of a life sentence.

[Those arrested today also included Sam Kikine and Isaac Ngcobo of the South African Allied Workers Union; Ismael Mohamed of the front's Transvaal Province branch, and Frank Chikane and Cassim Saloojee, both senior officials of the Democratic Front, the Associated Press reported.]

They will join eight other Democratic Front leaders charged with high treason in December, setting the scene for a major trial that is due to start in Durban on March 29.

The first eight prisoners, who included another of the Democratic Front's copresidents, Archie Gumede, have been refused bail. If the same happens with those arrested today, it could result in the country's most effective black political leaders being put out of action while the trial drags on.

The crackdown was also seen as damaging to a conciliatory image that President Pieter W. Botha has tried to project by making a conditional offer of release to the country's best known black political prisoner, Nelson Mandela, who has served 22 years of a life sentence for plotting the overthrow of white-minority rule.

Botha has said he is willing to release Mandela and begin talks with his outlawed African National Congress, provided the congress first renounces the use of guerrilla violence in efforts to end the segregationist system, called apartheid.

Mandela rejected the offer in a tough statement read for him at a Demoractic Front rally last Sunday in which he demanded that the white government should first re-nounce its commitment to apartheid and to maintaining white rule by force.

A spokesman for the Transvaal Indian Congress, a Democratic Front affiliate, said today that he believed the arrests made a mockery of Botha's offer to Mandela.

"Supposing Mandela had accepted the offer, how on earth would he have been able to work for peaceful change in this oppressive atmosphere?" the Indian spokesman, who did not disclose his name, asked.

South Africa's white-minority government staged a similar trial in 1956 when it charged 156 black leaders with treason.

Most were members of the African National Congress, which was then the major black nationalist organization.

The case lasted four years before collapsing for lack of evidence of any plot against the state. Soon afterward, the government outlawed the congress, driving it underground, and it then turned to guerrilla struggle.

The Democratic Front was formed just over two years ago as an alliance of more than 700 black community organizations and labor unions opposed to apartheid. It quickly developed into the country's most effective black political movement, and government spokesmen began describing it as a front for the outlawed nationalist movement.

There have been times during the past year when it seemed that the government might ban the Democratic Front as well, but it never did. Some felt this was because Pretoria did not want to tarnish the image of reformism that it was trying to project.

The government's patience began to wear thin last August when the front organized a boycott of elections for new parliamentary chambers. These were offered the mixed-race and Asian minorities in a new tricameral parliament, which was proclaimed as a first step in a process of incremental change. A number of front leaders were detained without charges and held for several months, as were some key black labor union leaders. These detentions triggered demonstrations outside the South African Embassy in Washington.

Most of the political prisoners were released early in December when President Reagan criticized their continued detention without charges after meeting with Nobel laureate Desmond Tutu. It was then that eight of those released were charged with high treason.