As the limousine of Julius Nyerere made its way through the White House gates on Thursday evening, a passing tourist asked the guard who the passenger was.

The guard, overheard by a Capitol Hill aide, replied, "It's the president of Tanzania, wherever that is."

Where Tanzania is, bordering on some of the most explosive southern African states, and who Julius Nyerere is, Africa's leading intellectural, are two of the reasons why his two-day visit to Washington this week has been so wrapped up in work, and minus the trappings of the usual state visit.

Nyerere, the leader of Tanzania since before its independence in 1961, is a man of spartan tastes and serious manner. so he seemed to enjoy the carousel of conferences and whirl of questions.

"Do you think that there will be a peaceful transition of powers in Rhodesia, Sir?"

Nyerere was seated on a red couch, a foot or two behind the microphones, as he started to answer the first question of the press conference. "Stand up, stand up, we can't bear you," someone shouted. "Oh, I should answer this question standing up," Nyerere replied, his small face ballooning into a smile. He seemd amused at the insistence of the press, its intensity, but understood the necessity of their catching his every word. He looked glum as he said, "The short answer is no."

It is the short and the long answers that Jimmy Carter, and his foreign policy advisers want to hear. It was both practical and ironic that Julius Nyerere was the first African head of state invited by Carter.

As spokesman for the nations that border the white-ruled countries of Southern Africa, Nyerere has been a key negotiator(with Zambia's President Kenneth Kaunda) between American and British initiatives, especially in Rhodesia, and black political leaders.

But his prestige extends far beyond those borders. In the last few months Nikolai Podgorny (then president of the Soviet Union), Cuban premier Fidel Castro, British Foreign Secretary David Owen and U.S. Ambassador to the United Nations Andrew Young had audiences with Nyerere in Dar es Salaam.

Yet, for many years his relations with the United States were cool, primarily because his economic building programs and political philosophy for Tanzania were based on an African socialism, not capitalism. The West saw red for many years. As the United States began to shape a dormant African policy into a major concern in the past year, Nyerere has moved into its circle of counselors.

In Tanzania he is known as the Mwalimu, the teacher. When Nyerere expounded on the role of South Africa in southern Africa at the working dinner at the White House on Thursday, Carter took notes for the first time during the evening.

Responding to a question by representative Charles Diggs (D-Mich.), chairman of the House sub-committee on Africa, Nyerere never raised his voice as he explained how the concept of apartheid must be changed, even if initially through the enfranchisement of the Indians and the coloreds. "That would be a break in the dam," said Nyerere.

"Do you think the American and British negotiations really put Smith's feet to the fire good enough?" asked Marilyn Robinson of NBC News.

"What is this expression 'held his feet to the fire?'" asked Nyerere. "Well, did they hold the screws to him?" Robinson pressed. "I have a feeling they did not screw him enough," said Nyerere with a laugh.

Walter Washington and Douglas Moore hopped into Blair House on Thursday to give the keys to the city to Nyerere. Moore, a city councilman who has lived in Africa and knows the continent's languages, upstaged the mayor. "I was going to do it in Swahili," said Moore, "but the language is not the same in Tanzania as in Zaire." Nyerere, said, very quietly, "It's still Swahili." "Why don't you just do it in English?" Washington said, rather sternly. They told Nyerere that the D.C. City Council had declared Saturday Julius Nyerere day. And at the end of their conversation Moore managed to get in some Swahili, saying, "I want to thank you" or "Nanina taka kusema."

It is said that Nyerere cannot be bought. He does not like compromise. "If I protect Africa for anybody, it will be to protect it for Africa," said Nyerere at a luncheon with several Senators yesterday. Coming out of the Tanzanian president, Sen. George McGovern (D-S.D.) said he admired his authority. "He's as impressive as any head of state we have had here," said McGovern.

Ujamoo! Ujamoo! (Familyhood) Uhuru! Uhuru! (Freedom) Mwalimu! Mwalimu! (teacher) . As soon as Nyerere stepped in view of the audience at Howard University yesterday, the shouts rang out. Nyerere smiled warmly and motioned the audience to sit down.

Yet, in his speech in front of the predominantly black audience that filled two auditoriums, Nyerere did not once mention the hot spots - Rhodesia, South Africa or Namibia. Instead he spoke of the economic struggle of poor people. "Our poverty has not arisen from our own actions or inactions in Tanzania," said Nyerere, moving back and forth on his toes. "The poor should not find themselves trying to run up the down escalator while the rich go sailing upward."