President Pieter W. Botha announced plans today that would redesign South Africa's pass-law system, one of the most hated symbols of apartheid, and offered to bring blacks into the highest councils of government in an advisory capacity for the first time.

In a State of the Union address outlining his government's avowed intentions to reform the country's system of racial segregation, Botha also made an unusual offer to enter into negotiations to release imprisoned African National Congress leader Nelson Mandela on humanitarian grounds if the Soviet Union would do the same for dissidents Andrei Sakharov and Anatoly Scharansky.

The proposals touched upon three of the most sensitive symbols of white-minority rule, although all the changes would be limited in impact or highly conditioned.

In the speech, which international bankers and businessmen regarded as a critical sign of South Africa's intentions to make changes, Botha declared: "We have outgrown the outdated colonial system of paternalism as well as the outdated concept of apartheid" and "we accept one citizenship for all South Africans, implying equal treatment and opportunities."

The most important items in the package were a scrapping of the hated "passes" that blacks must carry at all times and are used to restrict their movement into the cities, and the formation of a "national statutory council," which will include some blacks, to advise the government on new legislation and other matters.

Black leaders greeted the proposals with caution or hostility. They noted that the pass laws would be replaced by an identification system that could be used to the same effect, although whites as well as blacks would have to carry papers. They also scoffed at the limited governmental role being outlined for South Africa's black majority.

The proposals' presentation nevertheless stood in marked contrast to Botha's rigid posture in an address five months ago that exacerbated a run on South Africa's currency and caused severe unease in the country's business community.

In Washington, a State Department spokesman welcomed Botha's declaration that apartheid had become an outdated concept and said the United States remains "eager to see how (Botha's proposals) would be implemented." He also welcomed the proposal to release Mandela on humanitarian grounds, calling it "a step that could help break the stalemate in South Africa and lead to negotiations that so many have been hoping for."

Botha had ruled out the possibility of releasing Mandela in several tough speeches last year because the black leader refused to renounce his organization's commitment to guerrilla struggle, so there was surprise at his announcement today that he was prepared to link his release with that of Soviet dissidents Sakharov and Scharansky. Botha also included as a condition that Angola release Capt. Wynand du Toit, a South African soldier captured during a raid aimed at oil installations in Cabinda last year.

The nature of the offer, apparently a last-minute addition to his speech, left some observers puzzled and others angered.

Desmond Tutu, the black Anglican bishop who won the Nobel Peace Prize in 1984, denounced Botha in an interview, saying, "We are back at the old game of political point-scoring at a time when we clearly need examples of statesmanship."

In Harare, Zimbabwe, Secretary General Alfred Nzo of the banned African National Congress dismissed Botha's offer and said that Mandela must be released unconditionally, The Associated Press reported.

Others wondered whether Botha's surprising offer did not indicate a political move connected with some larger, still undisclosed negotiation involving Angola, South Africa and the United States.

An American diplomatic source said here tonight, however, that Botha's offer to release Mandela in part exchange for its captured soldier in Angola had come as a complete surprise to the United States.

"It is such a weird proposal that there must be more to it than meets the eye," opposition leader Frederik van Zyl Slabbert said. He said the offer enabled Botha to move away from his commitment not to release Mandela until the ANC leader renounced violence -- which Mandela was equally committed not to do.

For all the rhetoric of change, the code language of apartheid was still in the speech, as when Botha declared that "the peoples of South Africa form one nation, but our nation is a nation of minorities."

That embodies the underlying concept of apartheid: that the 28 million blacks do not constitute a majority over the 4.6 million whites but are a number of distinctive tribes, or "peoples," who should develop as separate political entities.

Many of the elements of Botha's legislative package had been foreshadowed in speeches during the past year. Botha said, for example, that laws will be enacted to allow blacks outright ownership of their homes and to restore citizenship to 5 million blacks whose citizenship is now tied to four tribal homelands. He had suggested both of these changes previously.

The proposals did not meet black demands for a one-man, one-vote majority rule system or for abandoning residential, educational and medical segregation.

The South African system also already contains a number of advisory councils -- notably a body called the President's Council -- but the purpose of the newly proposed council appears to be to give blacks a token role in a central government institution for the first time. However, that role is so peripheral that it is questionable whether many black leaders will be prepared to participate in it, especially in South Africa's current climate of intensified black radicalism after 17 months of racial unrest in which more than 1,100 persons have been killed.

Already leaders such as Tutu and Ntatho Motlana, chairman of the Soweto Civic Association, have dismissed the new council with scorn. "It will be able to deliberate but it will have no clout. It will merely act as a delaying tactic," Tutu said.

"We don't want all these contortions on the same theme of apartheid and white minority control," Motlana said. "We want a new constitution where we can all work for a free and just South Africa."

Chief Gatsha Buthelezi, the moderate Zulu leader with a strong following among his regionally based tribe, was less dismissive.

While stressing that the government would have to "scrap the idiom of segregation," Buthelezi said he was impressed by the sincere tone of Botha's speech and by the fact that the president would be chairman of the new council.

"That encourages me to believe that the government is giving the question of black political rights the highest of national priorities," he said. "If there is any prospect of the president bringing about real, meaningful change, I will certainly not be the one who undermines what he is doing."

Botha said the present system restricting the movement of blacks into the cities had become obsolete and costly. But he disappointed many by failing to announce acceptance of a President's Council recommendation that movement should be unrestricted in the future.

He said the government believes in "orderly urbanization," a substitute system of influx control that would allow only those blacks with jobs and housing to live in the cities.

Said Motlana: " 'Orderly urbanization' will just mean a new definition for influx control."

Initial reaction from the business sector to Botha's speech was moderately favorable, and the rand held steady on the London foreign exchange market this afternoon.