South Africa's policy of setting up independent tribal homelands appears to have made it all but impossible for many blacks to travel abroad.

In two recent cases, blacks who both oppose and comply with the government's policy have been blocked from traveling.

Three black nationalists who oppose the policy and refused to apply for citizenship in their homelands were prevented from traveling to the United States and West Germany because they have no South African passports.

Another black, who complied with the South African policy, obtained a Bophuthatswana passport but was unable to enter Malawi, a neighboring African nation, because it does not recognize the homeland as an independent nation.

The issue of citizenship for the 18 million blacks living in the South Africa has been described as "explosive" and is one of the major problems stemming from the government's plan to carve up a country that has been administered as one entity since 1910.

The separate development, or "plural democracy" policy, designed to prevent the country's 4 million whites from being politically "swamped" by nonwhites, aims at creating nine independent homelands governed by blacks.

But only 13 percent of the land - and none of the country's industrial or urban centers - is allocated to the homelands. Several, like Bophuthatswana, are made up of disconnected pieces of land.

The ruling National Party envisages an eventual confederation of the homelands and "white" South Africa, but the plan would leave the white minority in control because most of the land and economic power would be in white hands.

Only two homelands - Transkei and Bophuthatswana - have become independent so far, and no other nation has recognized them.

Many blacks, especially those living in urban areas, resent being told they are not citizens of South Africa, where they were born, educated and where they work. Most say that have never been to their "homelands" and do not wish to go.

About two million blacks - members of the Tswana and Xhosa tribes - live outside the homelands of Transkei and Bophuthatswana that have been reserved for them.

The dilemma was highlighted this week when a Xhosa speaker, university professor Wilkie Khambule, and a Tswana speaker, Nthato Motlana, were invited to West Germany for a conference. When they applied for South African passports they were told to get "travel documents" from their homeland governments.

The two men, both leaders of the black township of Soweto outside Johannesburg, refused to apply for the homeland documents because it would imply recognition of the homelands' independence.

"I would never consider the possibility of accepting a homeland passport," Motlana said. "I am a South African."

Khambule echoed this sentiment: "In the past two weeks I have tried three times to get a passport, but every time I am told to provide proof of my homeland affiliation with a certificate saying where my father was born . . . I have suffered much humiliation trying to obtain a passport and want nothing to do with the homelands."

Sipho Sepamla, a poet who won a national award last year for his creative writing, had the same problem when he was invited to visit the United States as a guest of the American Publishers Association.

On the other hand, Emily Banda, 50, a servant who had saved money five years for her first vacation trip and first plane ride, was prevented from going abroad when Malawi would not accept her travel papers from Bophuthatswana.

A spokesman for South Africa's Interior Ministry which issues passports said, "If a person is no longer a South African citizen he cannot get a South African passport. The law is the law. We only administer it and we cannot make exceptions."