The far right-wing Afrikaner Resistance Movement announced plans today for a mass rally that the government said would not be allowed, raising the prospect of another clash between South Africa's ruling National Party and the resistance movement, which broke up a major party rally in the northern city of Pietersburg last night.

The rally is scheduled for May 31, South Africa's national day, at the Voortrekker Monument, the most sacred shrine of the politically dominant white Afrikaners. The monument, on a hill outside Pretoria, commemorates the struggles of the Dutch-descended Afrikaner pioneers as they trekked in ox-drawn wagons into the interior in the early 19th century, fighting hostile black tribes.

Eugene Terre'Blanche, leader of the resistance movement, announced that he would address a Republic Day rally there May 31 together with the leaders of other far rightist organizations.

The government, which now seems committed to a head-on confrontation with the far rightists, immediately announced that the rally would not be permitted.

Although the monument's amphitheater has been used for years to stage big National Party rallies, its governing board announced today that it could not allow the shrine to be used for "political purposes."

Minister of Education and Culture Pieter Clase promptly endorsed the decision and said the government would not allow the rally to take place.

Terre'Blanche, in turn, vowed that the planned rally will go ahead in defiance of the prohibition. He contends that the monument "belongs to the volk" and that no Afrikaner can be prevented from using it.

This sets the scene for a repeat of last night's confrontation, when the resistance movement fulfilled a vow to stop Foreign Minister R.F. (Pik) Botha from speaking in Pietersburg.

Meanwhile, in a statement that could divide President Pieter W. Botha's Cabinet, Manpower Minister Pietie du Plessis, who is chairman of the National Party's northern Transvaal division, accused the police of aiding the resistance movement members who seized control of the meeting hall last night.

It was the first open allegation of what has been whispered in South Africa for months: that many police are covert supporters of the far rightist parties and that their political partisanship and excesses in the troubled black townships are condoned by Law and Order Minister Louis le Grange.

The charge is a direct challenge to le Grange, who is regarded as the most conservative minister in Botha's Cabinet. Observers here said that le Grange must either repudiate du Plessis, publicly revealing a Cabinet division, which is considered bad form in South African politics, or appear to concede the allegation of disloyalty.

In what may have been an attempt to demonstrate his loyalty, le Grange announced today that he had ordered a police investigation into last night's disruption of the Pietersburg rally, which took most observers by surprise.

A year ago the Afrikaner Resistance movement, which wants to reestablish the old Boer (Afrikaner) republics that existed before the Boer War with Britain at the turn of the century, was regarded as the lunatic fringe of the far right.

The movement is blatantly Nazi in both its symbols and its ideology. Its insignia is a slightly modified black swastika set in a white circle on a red background. It uses a Nazi-type salute and has a brigade of "storm troopers" who wear brown uniforms with high boots.

Despite the growth of right-wing support for the Conservative Party of Andries P. Treurnicht, few Afrikaners appeared to be taking the resistance movement seriously. But a month ago it suddenly hit the headlines when it drew a crowd of nearly 6,000 to a rally in Pretoria's city hall.

A week later its members packed a National Party rally in the country town of Brits, near Pretoria, and halted a speech by Deputy Minister of Information D.J. Louis Nel.

Violence between radical and conservative black groups continued to devastate the sprawling Crossroads shantytown outside Cape Town for the sixth successive day today, and the death toll rose to 32. An estimated 20,000 people are now homeless.

Police reported that they found five more bodies this morning of people who had been hacked to death with machetes.

The violence is between rival black groups battling for political control of the shantytown, which has an estimated 250,000 inhabitants. Radicals have accused the police of aiding the conservative groups and some white monitoring organizations have supported these allegations, but police authorities deny that they are taking sides in the fighting.

Elsewhere, racial violence continued to rage in many parts of the country and police reported another nine blacks killed in at least 35 incidents.