Nelson Mandela had no difficulty last week convincing official Washington that sanctions against South Africa should not be lifted now. But on the issue of whether direct assistance should be given to Mandela's African National Congress to encourage the democratization process, the signals were mixed, Congress saying yes, the administration no.

In March, Secretary of State James Baker said the United States should encourage nonracial democracy in South Africa '' ... the way it did in Nicaragua, if you will, where it {the assistance} went through the National Endowment for Democracy.'' The African National Congress, he said, ''will have a major role.'' Congress recently obliged by appropriating $10 million for a democratization program in South Africa, a large part of which the sponsors intended as direct assistance to the ANC.

This reflected a sensible approach, but strong opposition within Baker's party forced a change of position inside the administration. New concerns about aiding the ANC were raised when Mandela remarked favorably about three old allies, Yasser Arafat, Moammar Gadhafi and Fidel Castro, all of whom are justifiably on most people's short list of most-despised leaders. Nevertheless, we cannot attempt to work on democratization with other groups in South Africa and leave the ANC out of our assistance efforts, however troubled we are by some of its alliances.

Mandela has made it clear that his recent meetings with Arafat and Gadhafi and his statements of appreciation stem from the support they and Castro gave the ANC when many governments remained silent about apartheid. Nonetheless, Mandela undoubtedly returns home with a better understanding of the costs of this reciprocal loyalty. He should also see clearly the contradiction of urging world intervention in South Africa while suggesting that terrorism and gross human rights abuses by the PLO, Libya and Cuba are ''internal'' and beyond comment.

None of this changes the fact that Mandela has repeatedly called for a nonracial democracy in South Africa. This has been a principal tenet of the ANC since its founding in 1912.

The ANC is a large, complex organization with radical elements as well as more moderate ones. No one knows whether the formal ANC commitment to a nonracial, presumably multiparty democratic system will in the end be a stronger force than the desire of some for a single-party, socialist state. That is precisely why we should work with democratic forces within the ANC.

Those who want to block any democratic development assistance to the ANC because it has leftist tendencies risk creating a self-fulfilling prophecy. Avoiding involvement with the ANC may keep these critics ideologically pure, but this is not a prescription for a viable democratization strategy or for preserving American influence in a fast-changing situation.

Opponents of aid to the ANC raise the legitimate concern of its refusal to abandon publicly the "armed struggle." This is of course troublesome, because recourse to violence is never the preferred path to democracy. This is why Mandela's White House confirmation that the "armed struggle" is suspended so long as peace negotiations are underway is so significant. What he did not say is that the ANC abandoned this tactic almost two years ago. What is left is to transform a de facto condition into a formal declaration; this Mandela says he will do after the state of emergency is ended and ANC "prisoners of war" are released. This delay may trouble advocates of a strictly nonviolent approach, but it is certainly understandable in the circumstances.

Ironically, the de Klerk government has shown greater understanding for Mandela's position vis-a`-vis his constituency than the American critics of the ANC. After all, de Klerk chose Mandela as his interlocutor precisely because he hopes the ANC can deliver support from South Africa's anti-apartheid forces for a negotiated settlement, even from those most reluctant to forgo the armed struggle.

The ANC is now embarking on a political strategy to achieve a nonracial democracy in South Africa. We should not only welcome this policy, but actively support it. We can promote this peaceful course by helping provide the infrastructure the ANC requires to be politically engaged. Just as did the opposition "UNO" forces in Nicaragua and the Solidarity movement in Poland, the ANC needs material aid -- vehicles, regional and local offices, telephones, FAX machines -- to pursue the struggle for nonracial democracy. We should help other South African groups as well, but we cannot ignore the needs of the one organization the white government itself has recognized as its most influential prospective negotiating partner.

South Africa is at a crucial transitional stage. Just as Mandela today remembers his friends during the early days of his internment, so too will he and his ANC colleagues remember those who offered help during this historic period. The United States can either engage in a meaningful democratization effort in South Africa or leave the playing field to forces beyond our influence.

The writer is president of the National Democratic Institute for International Affairs.