Roger Naidoo has a one-room bachelor pad in the downtown commercial center here. The building is a bit seedy, and the landlord refuses to fix the elevator. But the 27-year-old clerk likes it because he can walk to work and no longer has to share an apartment with his brother and family.

But one night as he returned from his customary evening jog, Naidoo was handed a summons to appear in court on charges of living in a "white" area.

Every residential area in South Africa is allocated by law to one specific race under the Group Areas Act. Naidoo, as an Indian, is breaking that law.

The ancestors of South Africa's 750,000 Indians came from the subcontinent in the trade currents of the British Empire. Thousands of Indians and Colored (mixed race) persons -- some estimates say as many as 10,000 -- are living in areas designated "white" in Johannesburg's inner city.

Like Naidoo, many of them live in run-down neighborhoods, vacated by all but the poorest of whites, most of whom prefer the affluent suburbs. Like him also, many are new arrivals in the industrial heartland, in search of jobs. A recent government-supported study of migratory patterns found that skilled Colored workers are flocking to Johannesburg from their traditional home in Cape Town to take construction jobs that used to be reserved for whites. There are about 2 million Coloreds, 5 million whites and 20 million blacks in South Africa.

Other "illegal" tenants, like Abdul Samed and Khadija Cassim, were born in Johannesburg and have moved into all-white areas because of a critical housing shortage. Cassim, a dry cleaner who has three children, put his name on a waiting list in 1971 for a government house in Johannesburg's only legal Indian area, Lenasia, some 20 miles from the city. He is still waiting. In 1978 he moved his family into an old duplex in the white working-class neighborhood of Mayfair near his work.

This infiltration of Coloreds and Indians into white areas, like the recurring presence of black squatters outside Cape Town, illustrates the growing conflict between the country's segregationist laws, intended to keep cities white, and the increasing urbanization of other race groups in search of economic betterment.

As in the case of the squatters whom the government forcibly removed last August, the government's response to the Coloreds and Indians has been to force compliance with its segregation laws. Since 1977, more than 500 prosecutions have been initiated, according to Johannesburg's chief magistrate. The majority were dropped because the tenants moved -- many no doubt to other apartments in "white" areas. But this week the court began to hear the remaining 140 cases, including Naidoo's and Cassim's.

Their trials were delayed largely because of the efforts of a multiracial organization formed by "illegal" tenants and some concerned whites called the Action Committee to Stop Evictions (Acstop). Lawyers offering their services gratis were solicited to defend the tenants, bringing two test cases to higher courts that challenged the government's eviction efforts on grounds of necessity. Both cases were unsuccessful.

The government, which has been getting complaints from conservative whites, gave Acstop a tongue-lashing in Parliament last August. Community Development Minister Pen Kotze accused the group of helping "willful" people "to challenge the law." Kotze said he would introduce legislation to avoid the "time-consuming" legal procedure needed to get evictions.

"He's referring to us moving into homes in white areas as civil disobedience," said Acstop Chairman Cassim Saloojee. "We see it differently, we are forced to do it. We're saying the government is compelling people into a situation of civil disobedience. They don't want to come to terms with the fact that there is no housing for us."

In Johannesburg, the housing for these two groups is especially critical. Officials of Lenasia estimate that 1,900 families are living in rented garages, playhouses and other inadequate buildings. Cassim's 10-year wait for a house is common.

Last May, three days of rioting in the Colored neighborhood of Reiger Park that left two dead was sparked by frustration over housing. Local authorities there built 222 houses in two years for a waiting list of 2,230 families. Last August, the Johannesburg City Council admitted it had only 1,070 houses in the pipeline, with 4,903 families on the waiting list.

Researchers who have studied the Group Areas Act, and businessmen who are stymied by it, agree that the law is a chief cause of the housing shortage. Since its passage in 1950, 135,300 families have been resettled to achieve racially segregated neighborhoods, according to various studies. One percent of those families was white.

Funds used to move people and demolish their old homes could have been used to provide new housing for others, Acstop said in a report. Private developers see only frustration in the obstructions created by the legislation. The government fails to provide enough land for development of Colored and Indian townships.

"The constraint on housing is land," said Peter Badenhorst, director of one of the country's largest savings and loan associations. "But the real constraint is bureaucracy." Many Coloreds and Indians link their housing problems and their lack of political rights. "Last year we tried to see Minister Kotze," Saloojee said. "But there was a long delay before we got a reply to our letter and then they pushed us off to the deputy minister.

"But a group of white voters in Mayfair asks him to come for a visit and within a matter of days he goes to see them. It's because we do not have the vote and are outside this process of decision-making that he can merrily go along and refuse to negotiate with us," Saloojee said.

A government commission recently recommended that two neighborhoods taken from the Coloreds and Indians in the 1960s be returned to them. But the proposal was rejected. The government also dismissed as "political antics" a referendum in a plush white neighborhood outside Cape Town in which the voters asked that the area be opened to all races.

Segregated neighborhoods, the government insists, are "non-negotiable." Asked about a recent housing case, Black Affairs Minister Piet Koornhof replied that the evictions were "particularly hurtful...It makes us feel very sorry, and we are determined to move away from hurtful discrimination. But the law must be maintained."