JOHANNESBURG, DEC. 15 -- Members of the African National Congress today rejected a call from their own leadership to relax their sanctions policy against the white-minority government, even as the European Community voted to lift its ban on new investment in South Africa.

The ANC resolution, passed unanimously at the black nationalist organization's first conference inside South Africa in 31 years, appeared to be a sharp setback for ANC President Oliver Tambo and his international affairs chief, Thabo Mbeki, who had warned that international sanctions were crumbling and had called for a new policy on the issue.

Western analysts said the resolution raised questions about the ANC leadership's ability to convince the militant rank and file of the need to adopt more flexible policies to cope with the changing international situation. Some expressed concern that the organization's hard-line position on sanctions might affect the leadership's attitude toward negotiations with President Frederik W. de Klerk's government on the country's political future.

The resolution adopted by the conference called on the U.S. Congress, the European Community and other international bodies to defer all consideration of lifting any sanctions "until the ANC and all other democratic formations inside our country . . . initiate discussion with them on the issues."

Until then, it resolved that "the existing sanctions package be maintained."

The 1,600 conference delegates rushed to approve the resolution this morning in the hope of persuading the European Community to delay its decision, according to ANC spokesman Paulo Jordan.

But EC leaders meeting in Rome voted to allow new investments in South Africa to acknowledge Pretoria's political reforms, including the legalization this year of the ANC and other banned organizations, and the release of the ANC's long-imprisoned leader, Nelson Mandela.

The EC decided, however, that bans on imports of South African iron, steel and gold coins should continue until de Klerk fulfills pledges to abolish the racial segregation policies of apartheid.

The ANC resolution acknowledged the need to counteract a growing international perception that de Klerk's government deserves some reward for its reforms.

But it said the sanctions should remain in place because "the basic institutions of apartheid are still firmly in place," and it charged that the government continues to use "violence and police repression to suppress legitimate political and civic action." The resolution also accused "elements" of the South African security forces of being "deeply implicated" in recent violence in the country's black townships.

The decisions by the ANC delegates and the EC leaders came a day after Tambo had called for a relaxation of sanctions. Tambo told the ANC conference on Friday that it was no longer good enough for the organization to repeat the same old "trite" slogans about sanctions.

"We should therefore carefully reevaluate the advisability of insisting on the retention of sanctions given the new developments in the country and abroad," he said, warning that the ANC was losing "the strategic initiative" on the sanctions issue to the government.

Today, Jordan insisted that Tambo had only called for "a reexamination" of the sanctions policy. "When you say 'reexamine,' it doesn't mean you're going to change your mind. It means look at the issue afresh and see how you feel about it," he told a press conference at the ANC meeting site at an exhibition grounds near Soweto.

"If you think that the policy is still solid and is valid, you proceed with it," he said. "In other words, it should be on our initiative that sanctions are dropped. We will say when they are no longer necessary."

Jordan said there had been "overwhelming opposition" among delegates to any easing of sanctions, and he showed reporters a videotape of conference delegates applauding and then voting unanimously for the resolution, which was presented by Tambo.

Jordan called the EC decision to permit new investment in South Africa "unfortunate," and said it showed that "the EC is not convinced by our arguments. We will just have to argue again to convince them," he told the South African news agency, SAPA.

But South African Foreign Minister Roelof "Pik" Botha was elated by the EC decision. He said it vindicated the government's contention that sanctions were crumbling and showed that de Klerk's initiatives had started "a dramatic reversal in South Africa's foreign relations."

"It is positive recognition for President de Klerk's courageous steps," he said. "It is clear that the government's viewpoint that the process of change is irreversible is beginning to enjoy wider recognition."

It was reported today that Mbeki was the author of a draft discussion paper on sanctions presented to the conference suggesting that the group accept a de-escalation of sanctions in exchange for reforms by the government. This course was suggested, according to the paper, to avoid suffering a "major defeat" and "the international marginalization of the ANC."