When Fidel Castro gave his first interview to an American in four years, he sat down with Randall Robinson, the executive director of TransAfrica, the only lobbying group on African and Caribbean issues organized by black Americans.

When a State Department employe wanted to leak some internal memos on the Reagan administration's overtures to South Africa, he gave them to Robinson. When the Organization of African Unity asked a non-African for the second time in its history to speak to them--the first was Malcolm X--they invited Robinson.

Randall Robinson is a lightning rod for black American response to American foreign policy.

After Robinson released the State Department memos to the press, former secretary of state Alexander Haig said he wouldn't meet with a group of blacks if Robinson were included. At a recent meeting of the Council on Foreign Relations, Chester A. Crocker, assistant secretary of state for African affairs, was asked why the administration had broken relations with TransAfrica. He reportedly said, "We can't do business with people who steal documents."

That's quite a reputation for someone with a small plate of issues. But Robinson, 41, is a gutsy, commanding person, who laughs easily and is affectionately tagged "a Brooks Brothers revolutionary." In his Capitol Hill office, he describes his search for "a hedge against the notions of cynicism." He says quietly: "Change doesn't come, power is not shared, it is not conceded, it is not gained because people think it is the moral and ethical thing to do. Power behaves quite naturally, selfishly. To protect ourselves in the world, you have to grab the levers of power."

For Robinson, those levers have been used to exercise what former congressman Charles Diggs calls Robinson's "cutting-edge style." TransAfrica, now in its fifth year, has developed its own front line of action and accomplishments. When Ian Smith, the former prime minister of Rhodesia, visited Washington in 1978, the group organized demonstrations. When U.N. Ambassador Jeane Kirkpatrick met with South African intelligence representatives, TransAfrica called for her resignation. It is partly responsible for preserving U.S. sanctions against the Rhodesian government and helping to defeat the Reagan administration on its plan to renew aid to Angola. Last month, under its aegis, 24 national organizations released a paper condemning the Reagan policy in Namibia, a document used in the U.N. Security Council debate on Namibia last week.

Rep. Howard E. Wolpe (D-Mich.) chairman of the House subcommittee on Africa, says, "Robinson is one of the most effective witnesses we have ever had. TransAfrica takes on the highly volatile issues but also the less glamorous but equally important subjects, such as economic development."

TransAfrica often takes on its own constituency. After Andrew Young voted in the United Nations to allow South Africa to participate in the U.N. General Assembly debate on Namibia, Robinson took him to task.

TransAfrica's annual dinner tonight is now the third largest dinner of a black organization in Washington. The dinner and its chapter network are growing in what Robinson calls the worst of times. "This is probably the most anti-African administration since World War II," says Robinson adamantly.

The dinner, where the prime minister of Grenada, Maurice Bishop, will speak, is not immune from the same controversy as Robinson. A group of Grenadian exiles announced that they plan to demonstrate outside the hotel because Bishop's government is repressive. The other side believes that Bishop should have a forum, characterizing the treatment of Grenada as a classical case of racism in American foreign policy, citing primarily the United States' refusal to recognize its ambassador.

Among people who agree wholeheartedly with the goals of TransAfrica, there are some feelings that Robinson is ambitious, even arrogant--"a young man in a hurry" is one characterization--and that he has occasionally made tactical errors. Taking credit for the release of the State Department South African papers is one example frequently cited.

A lawyer by training, Robinson has the same towering--6 feet, 5 inches--and lean, fulsome looks and resonant thunder as his brother Max Robinson, a regional anchor for ABC News and the country's only nightly network black anchorman. The Robinson clan, which includes two sisters who live in Washington, Jewell and Jean, grew up in Richmond.

Randall Robinson's world was isolated from whites. "I was 22 years old before I met a white person whom I had a conversation with, other than across a counter in a store. I was 26 years old at Harvard law school before I sat in a classroom next to a white," says Robinson.

The Robinsons were primed on individualism, told to keep their own and others' feet to the fire. He squirms a little as he starts to talk about those values, saying he is embarrassed. "My parents were the kind of people who cared not so much what other people thought, but that other social forces didn't govern your activity, what you proposed to do was what you thought to be right. And damn the cost," said Robinson.

When he was 15, his sister Jewell recalled, Robinson spent his summer working in a grocery and gave all his earnings to his sister, whose college scholarship had been reduced.

In 1959 Robinson went to Norfolk State College and did his share of demonstrating at the local lunch counters. He served in the Army for three years and then finished his studies in sociology at Virginia Union University in 1967. After finishing Harvard law school in 1970, he stayed in the Boston area. He helped organized a takeover of the university president's office to protest Harvard's holding of Gulf Oil stocks and helped direct a boycott of Polaroid because of its links with South Africa.

The students, Robinson recalled, were the real risk-takers of the time. But he did his share. Later, when he was a staff attorney for the Boston Legal Assistance Project in Roxbury, he demanded that more black attorneys be hired and given more responsible positions. He was fired.

And his commitment extended beyond political action. He was so dedicated to dashikis, combat boots and fatigues that his mother had to request that he buy a suit and shoes for his father's funeral nine years ago.

In 1975 Robinson came to Washington, first to work for Rep. William L. Clay (D-Mo.) and then, for two years, for representative Diggs, whose office was the hub of black activity on foreign policy. The riots in the township of Soweto galvanized what for years had been only talk among the Africanists about the need for a black lobbying group to correct what Robinson calls "the sand of ignorance" on African issues.

Once the idea became a reality, Robinson's intensity was undiminished. "We were in Lesotho at an African American Institute conference, and a group went out to a restaurant and we were enjoying ourselves. And Randall made us focus again on the issue, how were we going to help those kids who had left South Africa and come across the border," remembered Anne Forrester Holloway, a former ambassador to Mali and now on the staff of the House subcommittee on Africa.

In the spring of 1977 TransAfrica was incorporated, and that fall at Max Robinson's Washington home the first fundraiser netted $7,500. Its offices have grown from one room, its budget is $400,000, the staff has eight full-timers and the general membership is 10,000. From the outset, TransAfrica made it a policy not to accept funds from any corporation that has investments in South Africa. Two years ago the group received foundation support to establish a monthly newsletter and a quarterly journal, which is now the most consistently published source in the United States of Third World thinking.

Robinson's own risks will continue. "We are making the most principled effort that we can. We don't want to be the kind of institution that came to do good and stayed to do well."