ATLANTA -- Weighing a crush of admirers who all wanted a moment with him, 71-year-old Nelson Mandela has axed a host of meetings and people from his grueling schedule in the United States. But a meeting with a millionaire public relations man from North Carolina, a former Nixon White House adviser, was one appointment he kept last Sunday in Boston.

Bob Brown, 55, a two-decade Republican, wore his trademark gray suit and burgundy tie. Mandela, African revolutionary, sporting a white hotel bathrobe, plopped down on a couch in his suite. He asked everyone to leave the room except the visitor.

"Even in a bathrobe, there's no doubt who's in charge," reflects Brown. Face to face, Mandela "has such a strong persona and a spirit of compassion. There's no ego, and I've worked for a lot of people with big egos in my time."

Indeed, with bosses ranging from Martin Luther King Jr. to former president Richard Nixon, Brown has hardly become a household name. Yet, by all accounts, in more than two decades, he's made millions as a quiet power broker for black America, straddling fences between the corporate and civil rights worlds.

As a public relations man based in High Point, N.C., Brown has made his mark brokering peace between corporations and the black community, hunkering down with sit-in demonstrators in Woolworth's around the South, working on labor problems for the textile industry and hearing out such firebrands as late Black Panther leader Huey Newton when Brown's corporate client feared Panther angst might threaten a nearby factory. "I used to hear people say, 'Looks like you're an Uncle Tom, one of those sellout niggers,' " he says with a laugh. "But that talk stopped after I got constant contributions to the {civil rights} movement from big corporations."

That's how the Southern Christian Leadership Conference and the NAACP paid their staffs in the early days, he says, from corporate funding, much of it engineered by Brown who at the same time was quietly teaching Fortune 500 clients how to be racially sensitive, how to protect corporate image (and market share) with black consumers and how good race relations are good for the bottom line.

Backstage, he also advised companies such as Hanes on how to desegregate their work forces in the heart of Dixie. "For us in the movement, that was no conflict," says Andrew Young, candidate for governor of Georgia. "The truth was we would have helped them desegregate for nothing." He chuckles. "But Bob developed a large PR portfolio advising major corporations on race relations. Still, he always maintained credibility in the black community."

At the same time he was serving white clients, he was raising money for a score of causes and holding down board seats on the SCLC and the Martin Luther King Jr. Center for Nonviolent Social Change here. He first met Coretta Scott King in the late 1950s when he was a volunteer with the fledgling SCLC, and in 1986 he accompanied the widow of the slain civil rights leader to South Africa.

There he met a frustrated Winnie Mandela. Her husband had been imprisoned for 23 years; she'd been trying without success to help her daughter get a college scholarship in the United States. Brown offered to do what he could, winning Nelson Mandela's personal blessing after an unprecedented (for a non-family member) visit to his jail cell.

Soon, he'd secured full scholarships to Boston University for Zenani

Mandela-Dlamini and her husband, Prince Thumbumuzi Dlamini. But the family had no place to live. Brown rented them a house. They had no car.

Brown bought them a van, he says. For the past three years he's supported the family, including three children and two relatives, to the tune of $75,000 a year, he estimates.

That's why Nelson Mandela kept his meeting with Brown, albeit in his bathrobe. The visitor recalls Mandela saying, "I want to thank you for what you have done for my family."

For Bob Brown, it's been quite a ride, bumpy at times, from a shoeshine boy whose great-grandfather was a slave, to one of High Point's first black policemen, to former president Reagan's first choice as U.S. ambassador to South Africa in 1987. Brown withdrew his nomination after reporters and government investigators began scrutinizing his business dealings with the former government of Nigeria.

But, in an interview here, he maintained there were never improper dealings, that his role in Nigeria was a "non-issue." Rather, he suggests, he was torpedoed for political reasons by some civil rights leaders he still regards as friends.

He took his name out of the hat, he says, "because of the way it erupted." Reporters camped at his door. His wife, Sally, was suddenly fearful of the spotlight such a job might entail. "I just felt the best way to help black South Africans was privately," he says.

"I objected to the plan, not the man," says the Rev. Joseph Lowery, president of the SCLC, "because he would have had to carry out Ronald Reagan's polices of constructive engagement with the South African government, which I felt were counterproductive."

He had no problem with Brown. "Bob's a Republican and believes in making money, and I have no problem with that, as long as it's honest," says Lowery, "but he's always supported human and civil rights; he's always been very effective in getting us what we needed."

Lowery credits Brown with unleashing millions of dollars for black colleges as a Nixon White House adviser, along with inspiring the administration's pro-black business policy.

Testifying on his behalf for the ambassadorship, Young said that Brown "was the only black Republican I knew who had the credentials to get along and work with Jesse Helms and Jesse Jackson."

"Bob Brown's public and private life demolishes the myth that only fashionable liberals support civil rights," said Nixon of his ex-White House aide. "He was one of the most dedicated, articulate and effective proponents of progressive civil rights policies" inside the White House and "played a major role in our successful efforts to peacefully desegregate public schools in the South."

Once, growing up in North Carolina, he wore hand-me-down clothes, his shoes stuffed with newspaper to fit, he says, holding forth from an ersatz French antique chair high above Atlanta in a private hotel club room. His grandmother adopted him after his parents moved away, and he helped her churn ice cream and fry fish to sell from a roadside stand.

"She put cardboard in my run-down shoes and compassion in my heart," he likes to say.

There's nothing flashy about Brown today, just a hint of gold (bracelet, designer watch). He's balding, wears tortoise-shell glasses and speaks softly in earnest tones.

After high school, he attended college for two years, then left to support his grandparents. He took a job as a police officer in High Point, then left for New York as an undercover agent with the Federal Bureau of Narcotics. He was on a live stakeout when he first met the special counsel for the Senate Rackets Committee. "It was Bobby Kennedy," he says. "He wanted to watch us bust a drug dealer."

After two years, he came home to start his public relations and market research firm, B&C Associates. He worked for the SCLC, raising money, then played fund-raiser for the presidential campaigns of John Kennedy and his brother.

During the sit-in days, Woolworth's was a client, its once segregated lunch counters targeted by civil rights protesters. It was Brown's job to see that they integrated peacefully. "I told the top executives that movement was moving ahead and there should be jobs and the lunch counters should be open without any arrests," he says, "and that became company policy."

That's where he first met Andy Young, Fred Shuttlesworth and other civil rights leaders. "I was always straight with them," he says. "They knew where I was coming from. I wanted to work out something to advance black people."

In fact, he was arrested during one protest and lost a few accounts. "People warned me I'd lose business, but I had to make a choice, if this movement was going on, if I helped open things up I'd benefit more than those on the front lines. Why shouldn't I make sure I was about the business that was going on?"

After the Kennedys and King were gunned down, he was organizing the black vote for Humphrey, but clients close to the Republican nominee Nixon urged him to help. He did such a good job, he was recruited as a White House adviser. He asked his old friend, Earl Graves, publisher of Black Enterprise Magazine, what he should do.

"I said, 'You're {kidding} me,' " says Graves. " 'I leave you alone for the summer and you go crazy? What do they want you to do?' So {Brown} says, 'Go to the White House and be a special assistant to the president.' I said, 'That's hard to believe.'"

After four years in the Nixon White House, Brown picked up his old clients, firms like Johnson Wax, Nabisco Brands, Woolworth's, and kept building his base, now employing more than two dozen people, alumni including Stedman Graham, a sports marketer who happens to be Oprah Winfrey's steady.

"He's probably one of the most powerful men in the country, not just black men," says Graham. "He can just pick up the phone and raise $100,000 in a few hours for a charity. At his company, {where Graham worked before leaving last year to start his own}, he gets calls from heads of state, or presidents of Fortune 500 firms."

He counts Oprah Winfrey as a friend and, after visiting South Africa with Graham, suggested how she might help. Since then, she has started a $50,000-a-year food program for elderly blacks in destitute black townships.

It was on a 1988 trip to South Africa that Brown got to meet Mandela in prison for two hours. He says Winnie Mandela was concerned about unauthorized use of the Mandela name to raise money, and there was discussion about how to protect the name, but Brown insists he never talked about obtaining Mandela's power of attorney to license T-shirts and products. He says he was instructed by Mandela to work out any strategy with ANC leader Oliver Tambo, his longtime friend.

But he says he was sandbagged afterward, accused of self-dealing, probably by turf-conscious ANC leaders and others who were jealous that he was the first American to meet Mandela in prison. "I was very hurt by those charges," he says. He says they never came up in his meeting with Mandela last Sunday. "All he wanted to say was thank you, and I just wanted to tell him how much we admired and respected what he was doing."