PRETORIA, SOUTH AFRICA, AUG. 7 (TUESDAY) -- The African National Congress announced early today that it will immediately suspend its 29-year armed struggle against white-minority rule in South Africa, while the Pretoria government said it would allow the phased release of an estimated 1,300 political prisoners and the return to South Africa of as many as 22,000 antigovernment exiles.

The announcements came in a joint statement at the conclusion of 15 hours of uninterrupted talks between negotiating teams led by South African President Frederik W. de Klerk and ANC leader Nelson Mandela that both sides said had cleared the way for full-scale negotiations to end apartheid and write a new power-sharing constitution.

"There will be no further infiltration of men and arms into South Africa, and related activities of military action will be suspended," Mandela told reporters at a 1 a.m. news conference. "We hope to be able to communicate with all our people and to inform them of what we have decided."

Mandela made it clear, however that "mass action" by South African blacks in the form of politically motivated strikes, consumer boycotts and street demonstrations would continue despite government demands that they, too, should cease.

"As long as there are no alternative mechanisms through which our people can address their grievances, it can be expected that mass action will be resorted to," Mandela said. "But if a mechanism is established at a national level which can be used to defuse the situation, then, of course, it will reduce that mass action."

{In Washington, the White House applauded the agreement, saying in a statement: "The United States has urged dialogue for bringing an end to apartheid. We hope this step facilitates this process. We are very encouraged and congratulate both parties for having made this important step forward."}

The government and the ANC also pledged to redouble their efforts to reduce the level of violence in the country, especially in Natal province where bitter fighting between rival supporters of the ANC and Zulu Chief Mangosuthu Buthelezi's Inkatha movement has claimed 3,500 lives over the past three years. But the government stopped short of suspending the state of emergency there, which the ANC had initially demanded as one of its conditions for agreeing to take part in comprehensive constitutional negotiations. De Klerk offered only the assurance that he would consider lifting emergency measures in Natal "as early as possible in the light of positive consequences that should result from this accord."

De Klerk also resisted an ANC demand for the scrapping of tough security legislation, particularly the Internal Security Act, which provides for indefinite detention without charges. He undertook, instead, to "continue reviewing" such legislation with a view to amending it at the next parliamentary session, which is scheduled for next February.

It was clear from both the joint statement and press conference that the ANC had retreated most in the marathon "talks about talks," with the government conceding little more than promises of future concessions. Asked about this, Mandela said that the ANC had decided before the meeting to suspend its armed struggle "in the interest of moving as speedily as possible toward a negotiated peaceful political settlement."

De Klerk was more circumspect, saying, "I have never approached the process of give and take in a materialistic way. We are not bargaining over the price of a house. We are concerned with the future of a country."

It was also clear that there had been sharp differences in the marathon bargaining session over the government's reluctance to yield to some ANC demands, particularly for official action to halt police violence against blacks.

When asked what the quid pro quo had been for the ANC's suspension of armed struggle, Mandela curtly referred the question to de Klerk. The president, responding somewhat hesitantly, said that the ANC had complained about police behavior but that it was the government's viewpoint that police "at all times deal with all problems in an even-handed manner" and would take disciplinary action if presented with evidence to the contrary.

Cutting in sharply, Mandela told the gathered reporters: "We in the ANC are, of course, not satisfied with that reply. We feel quite dissatisfied with the way in which the state organs are involved in the violence taking place throughout the country, especially in Natal. We have provided evidence in numerous instances, but nothing has been done. It is a totally unsatisfactory situation, and until the government has succeeded in taming the police, we will remain dissatisfied."

The talks, which took place in a generally enthusiastic and hopeful atmosphere fostered by both sides, were a follow-up to the first, historic meeting between the government and the ANC at de Klerk's Cape Town residence last May.

Still, despite the optimistic mood, many observers here pointed out that there would still be a serious divergence between what the government and the ANC expect from the coming constitutional negotiations.

As Hermann Giliomee, a political scientist at Cape Town University, has noted, the government would like to offer the ANC a coalition partnership in running the country, while the ANC seems to believe it can win total control if it exerts enough pressure and creates sufficient turmoil. Between those two perceptions, Giliomee warned, there is much room for further conflict and crisis.