It was never like this on the championship circuit.

Back in the good old days, before the gleam of diplomacy attracted Muhammad Ali, the champ could gauge his opponent: he knew the fighting style, he knew the size of the ring, he knew he could depend upon the support of the crowd.

International politics, Ali has found, is sometimes not so dependable.

As he brought his African mission for President Carter to Liberia, Ali said, "I have some control in boxing. But this is a game I can't control."

When he came to Africa last weekend, Ali was telling the world that Moscow had done something bad in the invasion of Afghanistan, a Moslem nation, and Carter's call for an Olympics boycott was just the right response.

His audience, it turned out, was not quite so receptive to the idea and Ali began getting some unaccustomed tough questions from the press at his first stop in Tanzania. Tanzania's President Julius Nyerere, one of Africa's most respected leaders, refused to see him.

After his roasting in Tanzania, and a later rough official reception in Nigeria, Ali began to change his pitch to suit his African audience showing a good sense of tactics when his opponent didn't quite fit the image drawn by his managers.

"The number one fight with me is not Russia," he declared in Nigeria. "The number one fight with me is South Africa."

During a reflective moment today, Ali admitted that he was not prepared for the strong black African antipathy to the boycott proposal. Neither, he said, were the American diplomats or officials traveling with him.

Tanzania's hostile welcome and his "50-50" greeting in Nigeria were an unpleasant surprise.

Although his receptions in Kenya and here were warmer, Ali continued to be grilled by local reporters about the lack of American support when more than two dozen African countries boycotted the 1976 Olympic Games in Montreal.

Today, relaxing in his hotel here in Liberia's capital, Ali admitted he had not anticipated his rough welcome. "No, no, no," Ali said, "But I don't think, as strange as it may sound, that the people who were traveling with me realized it either."

As Carter's envoy to Africa, Ali is traveling on a government jet escorted by Lannon Walker, deputy under-secretary of state for African affairs, Louis Martin, President Carter's White House aide on domestic minority affairs and other administration officials. None of them were immediately available for a reaction to Ali's comments.

"I think the American government don't realize" black Africa's feelings toward South Africa," Ali continued, "If they do, they're deliberately not doing anything about it" in relations with black Africa, he added.

The Africans' "main protest is South Africa," a tired, raspy voiced Ali said. "They're right. And why is America asking them to cooperate when America wouldn't cooperate in '76?"

Most of black Africa boycotted the Montreal Olympics in protest over New Zealand's participation.New Zealand, the Africa countries complained, had had sporting contacts with South Africa.

Nigeria announced today that it would take part in the Moscow Olympics. Tanzania is also expected to attend, as is Senegal, Ali's next stop.

In Western-leaning Kenya, along with Tanzania one of black Africa's top Olympic contenders, Ali met with President Daniel Arap Moi for a half hour in a meeting that was scheduled to last only a few minutes. Moi announced before Ali's arrival that Kenya would not attend the Olympics in Moscow.

Here in Liberia, Ali's fourth stop, the government announced two days ago that Liberian athletes would boycott, but pro-Western Liberia has never been a serious contender in Olympic competition. President William Tolbert is to meet with Ali Saturday morning.

Ali contends that the positive response to his mission has been "about 70-30," arguing that the majority of nonofficial Africans he has talked to have been favorably disposed to a boycott. Asked about his reception in Nigeria, were the press was stridently critical of him before his arrival, Ali said their reaction "was about half and half."

"They want to make their own decision," he said.

The Nigerians also told him, Ali said, that they are not interested in Carter's proposal because the Soviets sold arms to the federal government during their civil war a decade ago when "American wouldn't." Ali ran into the same argument in Tanzania about Soviet support for southern African black guerrillas.

Ali said he did not know beforehand how America is perceived by black Africa over the issue of South Africa or that it would affect his trip. But he said he feels it is necessary to complete the mission, a change from his assertion in Kenya that had he known about the role sports has played in connection with black Africa's animosity toward South Africa, "I probably wouldn't have" come.

He is continuing, he said because the Soviets train "a few blacks" to fight in South Africa "knowing we could only get killed, knowing we can't beat them." The Soviets do it to keep Africans quiet, he said.

One Liberian reporter, who declined to be identified, said Ali has been very popular in Africa up until now but doubted, after his trip, if the retired heavyweight champion's popularity would remain as high.

"We may or may not agree with the boycott," he said at the airport before Ali's arrival, but that is not the question. Ali is popular here, or rather was very popular, but it is an insult for Carter to send a black American here just because he is black."

Ali "is a boxer, but what does he know about African political questions?" he continued. "They just selected him because he is black. It's an insult."

Ali has defended his coming to Africa as Carter's representative on the basis of his being a Moslem who is deeply offended by the Soviet takeover of Islamic Afghanistan. "I am not here as the Uncle Tom pushing America's ideas on my people," he said.

"So I am not here just talking about America's wishes," he added.