JOHANNESBURG, DEC. 14 -- African National Congress President Oliver Tambo, addressing the first ANC congress held inside South Africa in 31 years, today strongly urged the black nationalist organization to consider easing its insistence on international sanctions against the white-minority government.

Home after 30 years in exile, including a year-long recuperation in Europe from a stroke, Tambo said it was "no longer enough for us to repeat the trite slogans."

"We should, therefore, carefully reevaluate the advisability of the retention of sanctions in view of the new developments in the country and abroad."

"At no stage should we allow the strategic initiative to shift to the other side," he added in apparent reference to the government of President Frederik W. de Klerk and its success in getting African and European nations to move toward dropping their sanctions, which have contributed to Pretoria's international isolation.

Tambo's appeal for reexamination of sanctions came as the 1,600 delegates to a national consultative congress began discussion of the ANC's policies on negotiations with the de Klerk government for a new constitution and programs during a transition period to a new non-racial government.

A draft paper, entitled "Managing the Period of Transition," warned that the ANC risked suffering "a major defeat" as governments begin acting unilaterally to ease or drop sanctions against South Africa.

The paper disclosed for the first time that the Soviet Union and Cuba are interested in establishing diplomatic relations with South Africa, citing the moves by the two nations as examples of such unilateral action. Moscow has decided to establish an interest section in the Austrian Embassy in Pretoria "despite our opposition to this move," and Havana is interested in "establishing a presence" here, the paper says.

The European Community and the Bush administration are expected to begin lifting a number of sanctions over the next six months, whether the ANC agrees or not, provided de Klerk keeps his promise to scrap the Land and Group Areas acts, which have assured the 5 million whites here exclusive control over 87 percent of the land.

The discussion paper was the frankest internal assessment ever published of the dilemma facing the ANC. It has not been approved by the ANC's National Executive Committee and is expected to be hotly debated at the three-day congress, several ANC officials said.

The "draft discussion document," as it is called, warned of a continual erosion of sanctions and the "international marginalization" of the ANC unless it took the initiative to propose "a well-considered program for the de-escalation of the sanctions campaign."

Otherwise, it said, "the perception will be created that the government has scored a major victory over the ANC having succeeded in persuading the world to lift sanctions contrary to the views of the movement on this matter."

The paper urged that a reduction in sanctions be tied to the process of democratic and non-racial reforms in the country and singled out for early reconsideration the ANC's educational and cultural boycotts as well as support for South Africa's return to international sports competitions.

The latter step, it said, should be taken on a sport-by-sport basis once each sport here has been integrated and placed under a single, non-racial governing body, and after the repeal of the Group Areas Act, expected early next year.

The paper opposes the lifting of financial sanctions or the arms and oil embargo so long as a white-minority government rules the country. But it says the ANC should offer to discuss the end of trade sanctions and to appeal for international aid, which should be channeled through an interim government in which the ANC and other black groups would be represented.

The de Klerk government has rejected the formation of such an interim government but hinted at some kind of consultation with the ANC and other black groups on forthcoming social and economic reforms.

The paper also proposes that the ANC begin a program of "contact and discussion" with the international business community to prepare for foreign investment in a post-apartheid South Africa. This should include discussion of an investment code, it adds.

Tambo, 73, who suffered a stroke in August 1989, delivered a 45-minute address to the congress held at a fair grounds outside Soweto. It was the first major speech he has given since his stroke, and he appeared in good mental condition, although he slurred some words and sometimes spoke haltingly. His right arm and side are still partly paralyzed, and he had trouble walking.

Tambo is expected to relinquish his post as president to Nelson Mandela, the ANC deputy president, at the end of the congress and return to London for more treatment after a visit of a month or two here.