The crudely painted sign over Rhiana Letoaka's hospital crib read "HOPE," but there was precious little of it in this overcrowded children's ward deep in rural Lebowa, one of South Africa's black "homelands."

She had the hollow eyes, graying hair and swollen belly of malnutrition. She was nearly 3 years old but, at 16 pounds, she was too weak to move or even cry. She only stared emptily and silently at the wall.

There were 30 small children like her in this ward at Jane Furse Hospital here, northeast of Pretoria, many of them two to a crib. All but two or three had serious nutritional deficiencies.

A few would die; others would gain weight temporarily, only to come back again in a few months. "We're fighting a losing battle," said Michaeline Mamakoko, a ward nurse. "Some mothers are ignorant, but most just don't have enough food."

It was a scene reminiscent of many an impoverished African country in the recent years of drought and famine. But it was taking place in South Africa, the subcontinent's richest and most powerful nation, one that has long called itself "Africa's breadbasket," and that takes pride in the comparatively high standard of living of its disenfranchised urban blacks.

This is the other face of apartheid.

While many children in South Africa's explosive townships battle the police, those in these remote rural areas face enemies that are equally relentless -- hunger, disease, poor sanitation and overcrowding. Its critics contend South Africa's system of rigid segregation has contributed to these conditions and to the impoverishment of a large majority of its black rural population.

The result, say doctors, nurses and relief workers, is a pattern of malnutrition and children's diseases that approaches the levels found in some of Africa's most destitute countries.

The official infant mortality rate for blacks is 80 per 1,000 live births, roughly six times higher than for whites. That puts blacks here on a par with comparatively better off African countries like Kenya, Ghana and Zimbabwe.

But that statistic ignores blacks living in the quasi-independent homelands, for whom the rate soars far higher -- as high as 190 per 1,000 in parts of the Transkei and Ciskei, according to University of Transkei researchers.

While there is virtually no malnutrition among whites, about one-third of South Africa's black children below age 14 are chronically malnourished, according to a 1984 study by Dr. John Hansen, retired pediatrics chairman at the University of Witswatersrand in Johannesburg. The death rate from malnutrition among black children under age 5 is 31 times that of whites.

For established black urban dwellers in Johannesburg and Cape Town, South Africa boasts a relatively high level of medical care. Although it is chronically overcrowded, Baragwanath Hospital in Soweto may be the largest and best equipped hospital for blacks in all of Africa.

But in the 10 rural homelands, conditions are often dismal. While the doctor-patient ratio for whites is one to 600, in the homelands the average is one doctor for 40,000 blacks, according to University of Cape Town researchers. In some of the homelands, according to Hansen, the proportion of malnourished children exceeds 60 to 70 percent. A Policy of Poverty

If apartheid touches every facet of South African life, it also touches death. Whites die of the diseases of western affluence, blacks those of Third World poverty.

South Africa's whites have one of the highest death rates from heart disease and circulatory ailments in the world, and the first heart transplant was performed at Groote Schuur Hospital in Cape Town in 1968.

Meanwhile, the largest killers of blacks are infectious and parasitic diseases -- including tuberculosis, typhoid fever, cholera and measles -- that are virtually unknown among whites.

South Africa's poverty stands out in part because it exists alongside such massive wealth. Twenty percent of the population controls 75 percent of the country's wealth, according to University of Cape Town economist Francis Wilson, who chaired the recent Carnegie Foundation inquiry into poverty here.

When the Carnegie study issued its results in 1984, South African President Pieter W. Botha reacted by criticizing the academics for focusing on this white-ruled nation at a time when famine was acute in many black-ruled states to the north.

The government virtually ignored the study's various findings and recommendations.

But although it does not approach the deadly levels of Ethiopia or Sudan, South African poverty also stands out, said Wilson in an interview, because "so much of it is a consequence of deliberate government policies."

"The biggest mistake one can make is to blame the drought for all the malnutrition," said Ina Perlman, executive director of Operation Hunger, a volunteer relief agency that is still feeding nearly a million persons despite the fact that for most of South Africa, the drought is over.

"It really dates back to the land acts early in the century," Perlman said. "They took the land away from these people and forced them into confined areas with poor soil and water. That's what made them poor and vulnerable, and the policy of restricting people to the homelands keeps them that way. The drought was just the cherry on top."

While most of Africa is seeking ways to increase food production by rural peasants, Perlman said, South Africa has been systematically dismantling its peasant farms.

While researchers estimate that at the turn of the century at least 80 percent of rural dwellers were subsistence farmers, Perlman estimates the figure is now down to 8 percent.

Those who left the land became seasonal laborers on South Africa's white-owned commercial farms. But the combination of five years of drought and growing mechanization have led to skeletal labor crews. In the corn industry alone, 250,000 workers were laid off, Perlman's group estimates.

The availability of seasonal labor, which is the major source of income for those remaining in the homelands, has shrunk to as low as 25 percent of the 1982 figure, she says.

The ideologues of apartheid who designed the homelands system contended that the various black states would become magnets for separate development of agriculture and industry. But Perlman cites experts who estimate that 70 percent of the supposedly arable land in the homelands is located in areas that the rest of Africa would consider marginal wasteland.

As a result, at least 9 million rural blacks live below the poverty line, and 1.4 million of them have no measurable income at all. Instead of attracting economic growth, the homelands have become human reservoirs of poverty where the risks for children are highest.

In Lebowa, for example, Machupe Mphahlele, secretary for health, estimates that nearly 50 percent of the homeland's 600,000 school children suffer from malnutrition.

Lebowa has its own separate administration although it has refused to accept "independence." But Jane Furse Hospital lacks many of the basic rural health programs available in some of Africa's black-ruled states, including Zimbabwe.

Individual health cards that record immunizations and the progress of a child's height and weight are not available. There is little or no instruction in oral rehydration therapy, an effective, low-cost method of maintaining adequate fluids and minerals in a sick child to avoid his becoming malnourished.

Birth control pills are free, but health workers here say they are not allowed to volunteer information on the subject because the Lebowa government views family planning with suspicion. Accordingly, families here are large -- seven live births per mother is the rough average.

Benedicte Iuel, a Danish physician who works in the children's ward, said she only admits the worst hunger cases because mothers generally tend to remain here with their children. When they do, said Iuel, "I worry about the children they are leaving alone at home." A Mirror of Rural Hunger

About 30 miles away from the hospital is the Nogoabe Clinic, where hopes are drying up with the drought, now in its fifth year. The village's only water pump has been broken since last October and the river bed is all but dry. A group of women who had been tending a modest vegetable garden for food to supplement their childrens' diet have given up because without water, the garden is dying.

"They say they want to do for themselves, but now there is no water," said Sylvia Kgoete, the clinic's head nurse.

Ten children have died here from malnutrition in the past three months, and a chart on the office wall records the rise and fall of hunger. The number of cases of kwashiorkor, one of the worst of the diseases of child hunger, dipped from 268 in August to 220 in January. Now, said Kgoete, it is beginning to rise again.

While black children in South Africa's rural areas are the worst off nutritionally, the diseases they contract there often follow them to the cities. Still, Crossroads, the massive shantytown east of Cape Town, has an infant mortality rate of 51 per 1,000, which makes it more than three times safer than the Transkei and Ciskei homelands that feed it a steady stream of at least 1,000 migrants each week.

Conditions in Crossroads mirror the worst of the homelands -- poor sanitation, lack of food and overcrowded shacks where infectious diseases spread rapidly.

The major difference is that doctors and clinics are more accessible, so sick children are often seen earlier and more frequently, before their infections become fatal.

Nonetheless, said Graham Bresick, a doctor at the Empilisweni Clinic at Crossroads, a church-funded organization that treats hundreds of children each week, "Malnutrition underlies almost all of the problems that I see. The diseases that healthy children ward off -- measles, diarrhea, just plain colds -- can do terrible damage to these children."