JOHANNESBURG, JAN. 6 -- South African security forces may have played a role in planning the violent destruction of squatter communities at Cape Town's Crossroads last year in which 53 persons died and 70,000 were left homeless, a New York-based human rights monitoring group said today.

The Lawyers Committee for Human Rights, in a 103-page investigative report released here, said that police were "centrally involved" with conservative black vigilantes in the razing of four squatter camps at Crossroads in May and June 1986.

The committee warned that incorporation of conservative black vigilante groups into official governing bodies is growing in many other areas of South Africa, threatening to escalate violence nationwide.

"The distinction between police and vigilante groups begins to blur as police provide arms to vigilantes, allow them to make arrests and even employ them as municipal guards," the committee said.

"Official tolerance of right-wing vigilantes has, in short, become a key element in the South African government's efforts to disable antiapartheid activism."

Citing scores of affidavits given by victims of the Crossroads attacks, the committee charged that members of the security forces handed out arms and incendiary devices to the vigilantes and actively participated in the burning of thousands of shanties occupied by militantly antigovernment activists, known as "comrades."

The committee said that four months before the attacks, which led to the imposition of a nationwide state of emergency, a police official met with conservative black leaders and reportedly directed the vigilantes to "destroy the comrades in the area."

The committee, citing residents' affidavits, said that a month before the attacks began, vigilante leader Sam Ndima told a meeting of Crossroads residents that police had given him firearms to use against the comrades. It said that two weeks later Ndima told another meeting that police had promised the vigilantes 600 guns for the purpose of driving out squatters.

While there have been numerous allegations over the last 18 months that police tacitly encouraged the vigilantes to destroy the squatter camps by refusing to intervene, the committee's report is the first by an independent monitoring group saying that the authorities may have planned the attacks and that they armed and actively led the vigilantes in the destruction.

The Lawyers Committee said its report was written by an American attorney who represented the committee in South Africa in 1986 and 1987 and who was in the Crossroads area during the attacks. Much of the evidence is drawn from affidavits submitted in connection with a court order last year prohibiting the police from aiding the vigilantes further.

The new allegations were made as a provincial Supreme Court in Cape Town considered the first of more than 3,100 civil suits filed against the government by victims of the Crossroads attacks, with claims totaling more than $2.5 million.

The government has denied that it participated in the planning of the attacks, or that it armed or even encouraged the vigilantes to raze the squatter camps.

It has characterized the destruction as the result of factional fighting between rival groups of blacks that it was unable to contain because of the density of the four squatter camps -- Nyanga Bush, Nyanga Extention, KTC and Portland Cement.

The police have dismissed meetings that security force members held with vigilante leaders prior to the attacks as routine contacts with the community to defuse a potentially volatile situation in Crossroads.

The Lawyers Committee traced the origins of the conflict to a 1983 power struggle between the comrades -- supporters of the militant United Democratic Front -- and the conservative vigilantes, known as witdoeke, an Afrikaans term for the white rags the vigilantes tied around their heads or arms during clashes.

As the UDF began gaining strength in Crossroads, the government enhanced the vigilantes' power by giving them informal authority to allocate sites for shanty dwellings, collect rent and even make arrests, the report said. This practice led to complaints of widespread corruption, and tensions in the squatter communities gradually rose, the report said.