Bishop Desmond Tutu, South Africa's Nobel Peace Prize winner, said yesterday that prospects for his racially troubled nation were "quite horrendous" and suggested that the country's white rulers might use nuclear weapons to carry out "their own version of a scorched-earth policy."

"I myself actually fear that in the end, because they are so irrational, they seem to have a Samson complex . . . They are going to pull down the pillars and everybody must go under with them," Tutu said in an interview with editors and reporters at The Washington Post.

"If, as most of us believe, they do have nuclear capability, I don't put it past them to have their own version of a scorched-earth policy," he said of the white minority regime in Pretoria.

Tutu is here on a three-week tour to rally American support for additional U.S. sanctions against South Africa for its apartheid policies. He painted a bleak -- and at times apocalyptic -- picture of his nation's future as well as that of black moderates like himself, who he said were increasingly shunted aside by blacks as "ineffectual leaders."

The 54-year-old Anglican bishop of Johannesburg somberly suggested that his patience is wearing thin in the search for nonviolent ways to overthrow apartheid.

"You may find," Tutu remarked, "that even placid, quiet people like us have suddenly picked up stones and we are fighting."

Tutu predicted the onset of "an ugly phase which has the potential for being horrible" in South Africa, a time of "naked terrorism, really." He warned that militant black attacks on "soft targets," such as school buses, were now possible. He also conjured up the image of black servants poisoning their white masters.

"Virtually all school buses in South Africa carry only white children," he noted. "They are the softest of soft targets."

The African National Congress (ANC), the main black underground nationalist group, has thus far refrained from attacking such targets, although Tutu said it would be "the easiest way of sowing panic in the white community."

But the Christmas bombing of a shopping center outside Durban, which killed six whites, "is an indication that we are in for a horrible time," he added.

"Most white households still have their morning coffee brought to them by black servants," he continued. "Supposing the ANC, or whoever is behind all this, were able to reach even just a quarter of those servants and say, 'Look, here is something that we want you to slip into their early morning coffee.' "

Tutu also disclosed that he and other moderate blacks met secretly with a ranking member of the South African cabinet, but said the session produced few results because the minister had insisted that the discussion be conducted "in the parameters of apartheid." Acceptance by the moderates of such ground rules would be "the kiss of death," he added.

Tutu chided the South African government for its "inept" relations with the nation's black majority, calling the country's white rulers "a centipede determined to shoot themselves in every foot."

The bishop also had sharp words for the Reagan administration's plan to channel covert aid to guerrillas fighting the Marxist government in Angola. Tutu denounced the notion as indicative of the administration's alignment with the regime in Pretoria in what he called "your geopolitical games of communism and Soviet expansionism."

"I am not interested in Soviet expansionism. I am not interested in communism," he added. "I am concerned about what is happening to our people now."

He also upbraided the Reagan administration for an "inconsistent" use of economic sanctions, charging the United States with adopting such measures "at a drop of a hat" against Nicaragua, Libya and Poland, but offering only "wonderful sophistries" to avoid imposing them on South Africa. The administration, under pressure from Congress, adopted limited sanctions against Pretoria last fall.

The Reagan administration is willing to "justify everything" because Pretoria "says it is anticommunist" and because "we've come to accept a thousand deaths because they are black."

Tutu seemed uncertain about his own fate at the hands of the white South African authorities. He noted that at end of March -- the deadline he has given the South African government to show it is serious about reform -- he would be courting arrest "by saying openly I advocate punitive sanctions."

But he expressed anger at daily police harassment of blacks, including the practice of stopping his car "virtually every day" in a search for guns as he drives home from work. He also complained that South African authorities are bringing foreign white tourists with police escorts to Soweto and his own home, treating the sprawling black township in Johannesburg like "a zoo" and its inhabitants like "animals."

"We are getting a legalized terrorism in South Africa," he said, citing the recent killing of a 4-year-old black child by police rubber bullets and the imprisonment of a 14-year-old boy for five months for throwing stones.

"People are upset and people are tired," Tutu added, "but I don't know what I'm going to do."