Bitter fighting broke out again today between rival black factions in Cape Town's Crossroads squatter camp as conservative vigilantes swept into another sector of the complex and set fire to shanties, putting 11,000 people to flight.

Thousands more fled from refugee centers where they had stayed since similar fighting destroyed three other sectors of the shantytown two weeks ago. South African police said they knew of six persons killed in today's fighting but expected the final death toll to be much higher.

Civil rights workers and reporters described the renewed fighting as even fiercer than the previous battle, which left 48 dead. They repeated accusations made then, that the police openly sided with the vigilantes against radical leftist groups whom they want to drive out of the area.

The renewed bloodshed in Crossroads came as 900 leading businessmen published a suggested reform program calling for black participation in the government and rapid advancement in the economy. The possibility of international economic sanctions against South Africa, absent such changes, was viewed here as more likely following the abandonment last week of a Commonwealth peace initiative.

The program, which is being circulated among government leaders, is being described as the most important attempt yet made by the business community to pressure the administration into making significant changes.

It urges the government to abolish a law that enforces separate living and trading areas for the different races and says there should be genuine freehold rights, access to property for all and multiracial central business areas.

In Crossroads, large groups of radicals and conservatives squared off across a strip of open ground near the sectors of the squatter complex that were destroyed in the fighting last month.

According to an official police report, the conservatives "swept through police lines" and attacked a squatter settlement known as KTC Camp, setting fire to the flimsy shanties. About 11,000 people fled the burning camp.

The vigilantes also set fire to a nearby welfare center where 2,200 refugees from last month's fighting were being accommodated by the Red Cross and other welfare organizations. The refugees and welfare workers fled the center, which was destroyed by the fire.

Other refugee centers also were abandoned as panic gripped an uprooted squatter community that now numbers about 45,000.

The accusation of police collaboration -- which officials deny -- starts with the contention that the authorities made a deal with the leader of the main sector of the squatter complex, known as Old Crossroads. His followers allegedly agreed to drive out the squatters from satellite camps that have mushroomed around the central one.

In return, Old Crossroads would be improved into a township with upgraded houses, paved streets and sports fields.

Those making the allegation say that the administration is trying in this way to achieve its long-sought objective of removing the squatter complex, at the same time crushing a strong radical movement.

Allan Boesak, a leading black activist, has described the action as "a forced removal of the worst kind."

Reporters from local newspapers said the vigilantes appeared to have many more guns than during the May fighting. Two reporters' cars were hit by bullets before police cordoned off the area and closed it to the press and a team of opposition legislators who wanted to make an inspection tour.

One team of reporters from the Cape Times said they saw police in an armored personnel carrier fire tear gas at KTC residents who tried to drive off vigilantes setting fire to houses 20 yards from where the police vehicle was standing.

The police did nothing to stop the arsonists, the reporters said.

A police spokesman, Lt. Attie Loubser, denied the accusations of partiality. "We tried our best to keep the groups apart," he said.

Five persons died in widespread violence elsewhere today.

Over the weekend, young black militants launched two hit-and-run attacks on shopping centers in white areas, as racial tensions mounted with the approach of the 10th anniversary of the 1976 Soweto uprising June 16.

No one was injured in the attacks. Spokesmen for activist organizations said they were the result of anger among young blacks at government action prohibiting meetings to commemorate the Soweto anniversary, which is the most emotive day in the black nationalist calendar.

Progovernment newspapers are suggesting that a state of emergency or even martial law may be declared if new security bills, which are being delayed by the Asian and mixed-race houses of the segregated Parliament, are not passed.