Nobel Peace Prize-winner Desmond M. Tutu returned home today to a rapturous welcome from his fellow black South Africans and seized his moment in the international spotlight to go on the offensive against the apartheid policies of the South African government.

As the white-minority government maintained its hostile indifference to his award, the Anglican bishop sought to use his Nobel Prize to turn world attention to the plight of what he called the "little people" who are victims of South Africa's system of racial oppression.

Echoing the rhetorical cadences of the late Rev. Martin Luther King Jr., whom Tutu says he greatly admires, the 53-year-old clergyman dedicated his prize to "the ones whose noses are rubbed in the dust every day."

Tutu also went out of his way today to restate his support for the outlawed African National Congress, South Africa's main black underground movement. From the assumed protection afforded by his newly enhanced international status, he seemed to challenge the government to prosecute him for that support.

At a press conference later, Tutu was sharply critical of the Reagan administration's policy of "constructive engagement" with South Africa, saying blacks here did not accept the administration's claims that it was encouraging reforms but perceived it as being supportive of "this racist regime."

The "real features" of apartheid, he contended, had gotten worse under the Reagan policy. Tutu said that shantytown dwellers were being harassed with "extraordinary callousness," blacks were being stripped of their South African nationality and made citizens of tribal "homelands," and South Africa had felt free to "bludgeon" neighboring black states into signing treaties with it.

"I cannot for the life of me see how anyone can see our position as having been changed for the better by constructive engagement," Tutu said.

"When Reagan came to power, I predicted that constructive engagement would be an unmitigated disaster," he continued. "After four years I believe it has been just that."

Tutu delivered his impromptu speech today to his colleagues at the headquarters of the South African Council of Churches, where the bishop is secretary-general.

"This award is for you, you mothers who sit at railway stations trying to eke out an existence selling potatoes, selling mealies corn , selling produce," Tutu said.

Referring to thousands of black migrant workers who leave their families in tribal "homelands" to work on renewable one-year contracts in the cities, the Nobel winner went on:

"This award is for you, you fathers who sit in single-sex hostels, separated from your wives and children for 11 months a year . . . .

"This award is for you, the 3 1/2 million of our people who have been uprooted and dumped as if you were rubbish. This award is for you . . . .

"It is for you who, down through the ages have said that you seek to change this evil system peacefully; for you who have marched against the pass laws peacefully and who, unarmed, have been shot, mown down and killed. With this award the world is saying it recognizes that you have been peace-loving to a fault."

Tears streamed down the faces of many of the bishop's listeners. Beyers Naude, a white Afrikaner dissident who recently was freed from a seven-year restriction order, wept and embraced Tutu. Naude told him: "I pray the day may come when my own people will understand something of the message you bring to black and white."

For blacks, Tutu's support of the outlawed African National Congress makes him a hero.

White liberals, however, are uncomfortable with the bishop's open support for what he calls "the aims" of an organization that has a military wing that is trying to overthrow white-minority rule by violent struggle.

To white opponents of apartheid, though they may admire Tutu, his support of the African Congress imposes enough of a distance to prevent the award of the Nobel prize from becoming a major new polarizing factor in the white community.

Tutu draws a distinction between the aims and the methods of the African Congress, to which he belonged before it was outlawed and driven underground 24 years ago. He says he supports its objective of trying to achieve a nonracial South Africa, which in practical terms would mean a black majority government, but that he does not support its violent strategy to achieve this, although he understands why it has felt driven to adopt this strategy.

The distinction is too fine to make Tutu a comfortable ally for anyone seeking votes in the all-important white electorate.

Support for the African Congress has been adjudged high treason by the South African courts, punishable by up to 15 years in prison. The courts do not give special treatment to those who attempt to distance themselves from the organization's military wing.

The enthusiasm of Tutu's welcome from the black crowd today contrasted sharply with the studied indifference of the South African government, which regards the bishop as a radical troublemaker. Both President Pieter W. Botha and Foreign Minister R. F. (Pik) Botha responded with a curt "no comment" when asked how they felt about Tutu being given the Nobel Prize.

Tutu told reporters he had received no word of congratulation from either the South African ambassador in Washington or the consul-general in New York before his departure from the United States yesterday. Tutu is spending the fall semester as a guest teacher at the General Theological Seminary in New York City.

The hostility behind this official silence has been reflected in the editorials of progovernment newspapers since the announcement of the award on Tuesday.

The biggest of these newspapers, a Johannesburg daily called Beeld, described the choice of Tutu for the peace prize as "the most amazing decision ever made by the Nobel committee."

Other whites have ranged in their reaction from enthusiasm among radical and church groups to cautious praise among more orthodox liberal opponents of the government.

The liberal Progressive Federal Party, which is the main parliamentary opposition, sent Tutu a message of congratulation yesterday. Its chief press supporter, the Johannesburg Rand Daily Mail, said in an editorial today that while it believed the bishop had made a "major error of judgment" in encouraging the withdrawal of foreign investments from South Africa, it recognized that "he offers the alternative of forceful dissent to people who might otherwise conclude that violence is the only solution".

Tutu said today he believed the only hope for a peaceful solution to the racial confrontation in South Africa was to hold a national convention of the "real leaders" of both communities to thrash out an agreed settlement.

But he said he believed the ruling whites would never do this of their own accord. They would do it only under pressure. This, said Tutu, was why he advocated pressure by foreign governments and agencies, including the divestment of foreign capital. "It is the only alternative to violence," he said.

The Nobel Prize-winner said this was why he was distressed by the Reagan administration's policy of "constructive engagement." Although the administration claimed the policy was encouraging South Africa to change, he said, it was in fact producing only token changes behind which the Pretoria government felt able to entrench apartheid in new forms, secure in the knowledge that it was protected by a superpower.

Asked at the press conference whether U.S. influence had not resulted in the lifting of about 60 restriction orders last year and the issuing of travel documents to government oppponents, Tutu included, the bishop replied rhetorically: "Do you regard that as a quid pro quo?

"The fact is that while most whites are hoping that Reagan will be reelected next month, most blacks are hoping fervently that he will not," Tutu said.