Nerves are taut in the tribal homeland of Venda after an attack by African nationalist guerrillas and a police sweep that followed in which 18 prominent people, including several churchmen, have been detained without charge.

The detentions, as well as other police actions, have engendered an atmosphere of fear and suspicion among authorities and residents alike in this beautiful, remote little territory that was given nominal independence by South Africa two years ago.

Monday Bishop Desmond Tutu, general secretary of the South African Council of Churches, said he had been expelled from Venda after trying to visit the detained clergy.

Speaking in Johannesburg, the black Anglican bishop, one of the most outspoken opponents of South Africa's system of apartheid, or racial separation, said he and the council president, the Rev. Peter Storey, were expelled over the weekend.

The tribal administration of the homeland, which South Africa installed although 80 percent of the population had voted against it, reacted sharply after an attack by African National Congress guerrillas on a police station in the main town of Sibasa last Oct. 26.

It feels particularly nervous because Venda is vulnerably situated near the borders of Zimbabwe and Mozambique, both of whose governments sympathize with the guerrillas' attempts to overthrow white minority rule in South Africa, whose independent homeland policy is a fundamental component of apartheid.

Among those detained since the police station attack have been three Lutheran pastors and their dean.

One died within 24 hours of his detention, and people who saw the body said it bore injuries indicating that the man, Tshifhiwa Muofhe, a young lay member of the church, had been beaten to death.

The dean, Simon Farisani, was reported hospitalized by other patients who said they saw him limp through the corridors with a badly swollen face. Earlier this month, the chief of the national force, Brig. Gen. Tshikhakhisa Mulaudzi, denied that the dean had been in the hospital.

He also denied persistent rumors that other detainees have been badly beaten. The police, he said, "are just asking questions."

In addition to the detentions, other indications of official edginess include frequent roadblocks at which travelers are stopped and searched, and the deportation of two clergymen who helped Muofhe's widow. The Lutheran bishop for the northern region of South Africa, Solomon Serote, was turned back from a roadblock when he tried to enter Venda to conduct Muofhe's funeral.

As a result of such actions, people say they are afraid to speak out.

The dean's wife, Regina Farisani, said she did not want to discuss her husband because she might be detained and there would be no one to look after their two young daughters.

A friendly official warned that all rooms in the only hotel in the capital, Thohoyandou, are bugged.

Even Serote, 100 miles away in the northern Transvaal town of Seshego, unplugged his telephone, which he suspected might contain a bugging device, before an interview.

The United States National Committee of Lutheran World Ministers has issued a strongly worded protest through its general secretary, the Rev. Paul A. Wee, at the treatment of the churchmen, and Amnesty International has announced it will investigate the detentions and reports of torture.

The homeland of Venda is one of the territories demarcated for the country's 11 main tribal groups by South Africa's white minority government to secure the main part of the country for whites. The homelands are being developed and coaxed toward independence in the face of strong opposition from African nationalists.

As a homeland gets independence all blacks whose ethnic origins relate them to the tribe concerned automatically become its citizens, wherever they live, and lose their South African citizenship.

One of four homelands to be given independence so far, Venda is the most remote, tucked away in the northeast corner of the country. It is a scenically beautiful little territory of forested hills and lush grassland just north of the Tropic of Capricorn. It is 2,300 square miles, less than half the size of Connecticut, and has a population of 400,000.

Patrick Mphephu, the man South Africa chose to carry out the homeland policy here, is a semiliterate clan chieftain.

South Africa created for him the position of paramount chief, which had never existed among the Venda before.

Opposed to Mphephu was a university-trained sociologist, Baldwin Mudau, whose policy initially was to opt for independence and then seek union with Zimbabwe.

The first elections in 1973 were under a constitution that provided for 18 elected members and 42 nominated chiefs and traditional headmen. Mudau won 14 of the elected seats, but after the chiefs and headmen had been feted at a nearby resort, all supported Mphephu and he became chief minister.

For the pre-independence elections in 1978, Mudau again won handsomely, but Mphephu then detained several of Mudau's elected members under emergency powers given by Pretoria until after Parliament had voted him prime minister. A year later he was installed as president.

With power and an annual aid budget of more than $50 million from South Africa came status and affluence for the largely uneducated chiefs and headmen allied to Mphephu.

They acquired large limousines and huge houses in the midst of an overwhelmingly peasant community.

They also attracted the friendship of businessmen with a sharp eye for an opportunity, and Venda is rife with rumors of corruption.

The guerrilla attack hit this scene like a bombshell.

"They know they have no roots of popular support and they panicked," said one of the deported clergymen, Faure Louw, whose Dutch Reform Church is one of the bastions of support for the South African government and the homelands policy.

"But I know most of these people who were detained . They were involved in church affairs and are strongly against violence," Luow said. "I am certain they had nothing to do with any subversion."

A statement issued by the vice president, Khosi Madzivhandila, justified the detentions on the grounds that the attack on the police station was by "revolutionaries and terrorists" and that "it is the right of every government to protect itself and its people."

Brig. Gen. Mulaudzi, who expressed anger at the press for maligning Venda, refused to discuss the dead detainee, saying the matter was being investigated.

Mulaudzi, formerly with the South African security police, said he saw nothing wrong with detention without charges.

"We do not call it detention without trial," he said. "It is a form of investigation. I think it is the best way. When you have a person there, by himself without any influence from others, then you get the correct information."