A series of actions by security forces of the white minority South African government against members of the newly emergent black labor movement has caused labor leaders to identify more closely with black political activists.

Until a few months ago, the major unions resisted efforts by black political movements to involve them in their campaigns against apartheid. They reasoned that building up their shop-floor strength was a priority task.

But attempts by the government to quell unrest in segregated townships since the trouble began last September is changing the attitude of black labor leaders.

Evidence of this change appeared at the funeral Tuesday of a union official who died shortly after being arrested by the police in a trouble-torn township called Tsakane, 50 miles east of Johannesburg.

The official, Andreas Raditsela, 29, belonged to one of the most determinedly nonpolitical union groups, but the funeral it organized for him turned into a political mass rally attended by more than 25,000 people.

Leaders of the union federation, known by its acronym, FOSATU, delivered impassioned speeches in support of the black demand for political rights. Their union songs mingled with those of the underground African National Congress and its guerrilla wing, Umkhonto we Sizwe (Spear of the Nation), in Tsakane's packed Methodist church, where the funeral service was held.

A huge banner on a wall behind the pulpit proclaimed Raditsela a political martyr with the epitaph: "His blood has watered the tree of our struggle."

FOSATU's president, Chris Dlamini, said in an interview that Raditsela's death was a watershed event for the union federation.

"I think we have reached a new stage now," he said, adding that unrest and bloody clashes with the police that have resulted in more than 300 deaths and 10,000 arrests in eight months are "pushing everyone into becoming involved in political issues outside the working place."

Earlier, three bombs exploded at government buildings in the nearby white town of Brakpan, causing extensive damage but no casualties, and leaving the impression that the Spear guerrillas were attempting to identify with the day's symbolism.

However, a call for a one-day general strike by FOSATU to mark the occasion was observed only partially, indicating that while the unions are becoming politicized, South Africa's deepening economic recession and rising black unemployment rate are limiting their ability to take effective action.

The first step toward politicization was taken when the administration of President Pieter W. Botha ordered the Army to encircle four black townships in the Vaal Triangle region south of Johannesburg last October, while police conducted house-to-house searches for "revolutionary elements" allegedly behind the wave of unrest then just starting to sweep the country.

Although more than 500 people were arrested in the predawn raid, all were charged with minor violations of apartheid laws. The operation succeeded only in angering the 100,000 township residents, many of them industrial workers who put pressure on their unions to resist.

The unions did this by calling for a two-day protest strike. The government responded by arresting FOSATU's Dlamini and Piroshaw Camay, president of another big union alliance known as CUSA.

Dlamini and Camay were detained without charges for a month under security laws before pressure -- apparently from the Reagan administration -- secured their release. By that time FOSATU and CUSA, with a combined membership of nearly 300,000, had drawn closer to the main black nationalist organization still allowed to operate legally, the United Democratic Front.

Raditsela's death has given FOSATU another shove in that direction. The next step toward a South African Solidarity-type labor movement could be taken June 8 and 9, when FOSATU, CUSA and other major unions are due to meet to discuss the possibility of forming a single black labor federation.

Raditsela was not a major figure in the union movement, but he was well liked in the Dunlop tire factory at Brakpan, where he was a senior shop steward for the Chemical Workers Industrial Union, a FOSATU affiliate. He was also a vice president of FOSATU's Transvaal provincial division and a member of its national executive.

On May 4, colleagues of Raditsela saw police arrest him in Tsakane, a township where 31 people have died in unrest over the past two weeks. They claim they saw a police officer strike him on the head, knocking him down. He was then dragged away and put in a police van, they said.

Later that day relatives found Raditsela in a disoriented state, lying on the floor of an official building. He was taken to a hospital where he died May 6.

A post-mortem examination has revealed that he died of a subdural hemorrhage, which a pathologist has said is consistent with a blow to the head.

While white South Africans are waiting for the formal verdict of an inquest, the black unionists are convinced by circumstantial evidence that the police killed Raditsela.

At the funeral, there was a note of outrage in the speeches. A spokesman for Raditsela's family, dressed somberly in a black suit, thanked the union for "blowing the cover off what happened to our brother." A shop steward from Dunlop spoke of "the slaughter of our comrade."

As the four-hour service ended, the pall-bearers moved in procession through a huge crowd of people who stood silently outside the church with their fists raised in a forest of black power salutes.

Police and troops in armored vehicles took up positions in side streets and two police helicopters circled overhead as the crowd, swelling as it went, followed the coffin on a two-mile procession to the cemetery.