At first glance it looks like business as usual at the Checkers supermarket in the Sandton shopping mall here. Customers wheel shopping carts down well-stocked aisles with a quantity and variety of products that would look familiar to any American shopper.

But almost all of the customers are white and so are most of the checkout cashiers. Black faces, which usually predominate behind the counters here, are conspicuous by their absence.

The reason is that members of the Commercial, Catering and Allied Workers' Union have walked off their jobs to protest the arrests of many of their leaders during South Africa's two-week-old state of emergency. This store is one of more than 100 stores, factories and warehouses to be hit by wildcat strikes since the crackdown began.

At least 171 union leaders and shop stewards have been arrested since the state of emergency began June 12, according to the nonprofit Labor Monitoring Group, which keeps tabs on the union movement. It says at least 85 percent of the detained are members of the South African Trade Unions, or Cosatu, the country's newest and largest union.

At least 16 union leaders have been released in the past two days, including 10 Cosatu officials. Four officials of the rival 180,000-member Council of Unions of South Africa, including its general secretary, Piroshaw Camay, and two leaders of the commercial catering union were also released.

By American standards, the strike here is an odd, virtually invisible one. There are no picket lines and no protest signs. Such demonstrations are illegal under South African law and would result in certain arrest. Union leaders say hundreds of workers who have tried to stage sit-ins or other protests in a number of factories have been quickly rounded up and detained under the emergency regulations.

But the strikes continue, reflecting the fact that South Africa's two-week-old state of emergency has become, in part, a test of strength between the white government and the country's young but growing black trade union movement. It is a test that has found the white business community caught in between -- beseeching security officials to release union leaders in order to get their employes back to work.

"I feel like the ham in a sandwich," said a business executive who was part of a group who met with Law and Order Minister Louis le Grange last week. "We've spent years building up excellent relations with our unions, but now that trust is starting to disintegrate overnight."

Union organizers have allegedly been threatened with detention unless they stop recruiting. Those wearing union T-shirts or displaying union calendars have also been harassed. Shop stewards have disappeared.

The unions are a relatively new target. Last year's emergency was aimed largely at political leaders, community activists, church leaders, teachers and students who had long found themselves on the receiving end of government crackdowns.

Now the more activist unions also have joined the list. The reason for the change, both the government and union leaders agree, is that the unions in recent months have begun to shed the relatively apolitical stance they had adopted early on for their own protection, and have ventured into South Africa's volatile and risky political arena.

"No member of trade union movements in South Africa is being detained under the emergency regulations because of purely trade union activities," said Commissioner of Police, Gen. Johan Coetzee, in an unusual statement released yesterday. Instead, he said, police had arrested unionists who had "entered the political arena with full knowledge of the possible repercussions and implications thereof."

"The government is trying to destabilize the trade union movement," said Marcel Golding, spokesman for the National Union of Mineworkers, the country's largest black union and a Cosatu affiliate. "They're warning us that we're vulnerable and that they can hit us if they choose to."

Golding and union general secretary Cyril Ramaphosa went underground for two weeks after police surrounded their downtown Johannesburg office building and searched the premises for them. Cosatu president Elijah Barayi and General Secretary Jay Naidoo also disappeared for a time. The two top officials of the Metal and Allied Workers Union, another major Cosatu member, have remained out of the country since the emergency began.

"The emergency has hit us very severely," Naidoo told reporters after reemerging this week. He said 70 key leadership figures in the movement had been detained and he warned that wildcat strikes by retail workers could spread if the government did not take heed.

The black union movement has historically led a precarious existence in this white-ruled country. More than two dozen unionists were banned in 1976 following the Soweto student revolt and some union leaders have spent many years behind bars.

But the movement survived and in 1979 gained a major victory when the government legalized union membership.

At first the new unions shied away from politics, fearing they would be crushed in their infancy under South Africa's stringent security laws. But as civil unrest in black townships and violent clashes with riot police have increased, the unions have come under strong pressure from community activists and their own rank-and-file membership to get involved.

"We could not allow our children to continue dying," said Lucas Radebe, a Cosatu activist and factory shop steward who lives in Kwa Thema, a township east of Johannesburg. "We had to take a leadership position in the movement."

The formation of Cosatu last December in Durban was the culmination of this political trend. The federation, which claims to represent nearly a half million workers, took strong stands against the apartheid system, most notably the laws that required blacks to carry passes. The laws have since been abolished. It is identified closely with the United Democratic Front, the main antiapartheid coalition.

The detentions were a major problem for some businesses. When retail workers began wildcat strikes against Johannesburg's largest chain stores last week, employers phoned the union for help, only to find that the leaders they had negotiated with for several years were in jail.

As a result, the businessmen petitioned Law and Order Minister le Grange for help. "We urge you to reconsider your policy," Anthony Bloom, chairman of the Premier Group, a major industrial and retail conglomerate, wrote le Grange. "We are now faced with attempting to run our factories and enterprises by dealing with the mob, as the leaders are in custody." No one will divulge what le Grange told them, but many businessmen see the release of some union leaders this week as an indication that their concerns have gotten through to Pretoria.