TANZANIA is one of the poorest 25 countries in the world. But in political weight it may well be in the top 25. This extraordinary accomplishment is the work of its first and only president, 57-year-old Julius Nyerere, who has been ruling now for 18 years, longer than any other post-colonial African leader. To the outside world, it is his pivotal role in Southern African diplomacy that has won him attention.

Ever since Henry Kissinger, in a rushed last-minute effort at the tail end of his tenure as secretary of state, tried to find a formula for ending white rule in Rhodesia, Nyerere has been courted by the West as the most important influence for accommodation on the African side. At first sight it is odd that this should be so. After all, Tanzania's border is not contiguous with Rhodesia or South Africa. Its economic and military strength is slight.

The answer is rooted principally in Nyerere's personality, the fact that he has never shied away from helping the liberation movements in Southern Africa, whatever his own difficulties at home. It was from its bases in Tanzania that Frelimo toppled Portuguese colonialism in Mozambique. And Dar es Salaam has long been the headquarters of the Organization of African States' liberation committee.

We talked for over four hours in his small seaside house where he now conducts most of his business. In 1972 he moved out of the magnificent Britishbuilt State House, which he found more like "a hotel than a home." We sat on the veranda, his shoeless feet tucked under him, his manner as unpretentious as his lifestyle. (He lives on a salary of $500 a month, less than his senior civil servants.) Even in his most forceful moments, when he was for the first time publicly damning the American and British diplomatic effort in Rhodesia, his voice never became harsh. There was always a laugh or a gesture to mellow the attack.

Nonetheless this interview, calling for all-out war in Rhodesia, could mark the end of the era of diplomacy in southern Africa.

Let's talk about Rhodesia. With the majority of voters in the Jan. 30 white referendum voting for black majority rule on the lines worked out by [Prime Minister] Ian Smith and his black supporters, isn't it time to reconsider your support for the guerrillas of the Patriotic Front who are trying to undermine this "internal settlement "?

No! Smith has not changed. What has happened is that the Patriotic Front has been fighting and Smith now realizes that he will lose that war. He has to see what he can salvage. I know what that "internal settlement" constitution is. It is a kind of constitution which secures power for a white minority for the next I-don't-know-how-many years.

Whatever you say, Rhodesia will have an election on April 20. The international press will be there in force. If they see that the election is reasonably free and as fair as one can expect in a war zone, it is likely that there will be a move in Congress to lift U.S. economic sanctions against Rhodesia. And maybe in Britain there will by then be a new Conservative government led by Mrs. [Margaret] Thatcher. Are you worried about this possible turn of events ?

Yes. It would be dishonest to say that I am not worried. I have always worked to try and get western pressure on the side of the liberation forces. We have got to maintain this support because it is useful. However, if things go as you say they might, then Britain and the United States would have joined the enemy. We'll have to live with it. We shall fight them. If the Patriotic Front is still willing to fight them and the Russians and the Chinese and the communist countries are willing to give us the arms, we'll fight them.

Is it still possible to bring peace and democracy to Rhodesia ?

My answer is yes, of course. That war is going to end. It will come to an end and the guerrillas will win. Can one hope that there is an alternative to war? I think not.

Less than a month ago you told an American reporter that you wanted a "short, sharp military action" by the British and the Americans in Rhodesia. You were still arguing for it only a month ago .

I've given up.

So this change of mind is fairly recent .

I've been talking like this for years, mostly privately. I began to talk like this publicly only recently. "Go in. Go in." I said. There was no sign -- none. None at all. And now I've got to concentrate on the only alternative, which is the war.

When I believed there was some hope of ending this war on the basis of the Anglo-American proposals I spoke in their favor to my Patriotic Front colleagues without any inhibition. I was very firm. There came the time that I was almost the only one that held to them. Washington was shy about the Anglo-American proposals. London was even more shy about the Anglo-American proposals.

Now I know there is no hope at all of moving Washington or moving London on the Anglo-American proposals or trying to implement them. They play around with them as a kind of phrase. "The Anglo-American proposals remain the best basis of a solution," but you don't have to do anything about it. So realistically the Patriotic Front must concentrate on the only alternative, which is to win the war.

In this fight to the finish which you foresee you have mentioned that you will go to the communist powers for help. How deep is that involvement likely to be? Are we likely to see Cuban troops brought this far south ?

No. What for? These people are winning that war without Cubans. So what do they want the Cubans for? The Cubans can't liberate these people. These people want to feel they have liberated themselves.

You don't see the South African government at a point of crisis being driven by its own public opinion to get involved and that producing a Cuban involvement ?

Oh, yes, there can be a repetition of Angola. But it will come from South Africa and the West. It will not come from here. Why? Because the Patriotic Front is winning that war. Left to themselves, they are winning. They are winning, Smith says so.

So when you talk of increased communist support for the Patriotic Front what were you thinking ?

Remember, we were talking about the possibility that after the so-called elections in April, the West would decide to back up the resulting government. The West at present, whatever their sympathies, are not backing up that government of Smith. But if they decided to back up the government which results after the 20th of April, this will change the situation and then we may need a lot of support from the communist countries.

Even Cuban troops ?

It depends upon what they do.

So you won't rule it out ?

The Patriotic Front will have to decide the kind of support they want from their own allies. I hope we don't need them.

But if the U.S. Congress did lift sanctions and Mrs. Thatcher attempted to be accommodating to that April 20 election and the South Africans continued to give whoever became the black prime minister arms supplies and maybe other forms of military support, wouldn't there then be enormous pressure within the Patriotic Front to ask for Cuban help ?

If that happened I hope the Patriotic Front would still say nothing has changed except that the enemy has been propped up. I hope that at least it would help them to solder their unity. Whether the Patriotic Front will decide to involve their allies in anything more than supplying them with arms will depend upon the real situation in Zimbabwe.

This supply of arms in itself poses real problems, because the Soviet Union is the principal supplier of Joshua Nkomo and China is the principal supplier of Robert Mugabe. We have already seen with Vietnam and Cambodia these two superpowers using smaller nations as proxies. Do you see a basis for further divisiveness in the source of the arms supplies ?

Yes. I see that danger. We are very frank with both the Chinese and the Russians. We hope they will not join the enemy by working for the disunity of the Patriotic Front. We are very frank.

During the last 12 months there have been reports of savage killings of innocent civilians, even missionaries, by the Patriotic Front. What do you make of these reports ?

I have no reason to believe them. I

The issue is not what constitution there should be for an otherwise democratic South Africa. If that was the issue, frankly I would leave it to the South Africans. The issue is this: Here are people with a religion. Their religion requires that they must govern the blacks. There are governments in the world we criticize, including a government like Idi Amin's, because he is killing people. He is a murderer, he is a tyrant. But he doesn't have a religion which requires that he kill people. This superiority based on the Bible is really nonsense, and therefore the people will have to fight.

Is there a way of bringing majority rule to South Africa without the kind of fighting and killing we see unfolding before us in Rhodesia ?

Yes, the choice is there. The South African whites could say, "Look, we have been on this course now for more than 30 years. We don't appear to be converting the world at all to our course. Perhaps we have lost. Perhaps we need to change. We need to treat the majority of our people as human beings. So let us begin the process of change."

In 1966 you said that the United States, "instead of taking the revolutionary side as its history suggests it should, has always taken the side of European colonialism." Do you still think that ?

I wish I could say I am wrong now. I think the failure in Rhodesia was basically because the Americans decided that they must listen to the British. They will only do as much as the British are willing to do. I thought for a time that Carter was going to try to use American power much more vigorously in helping to end some of these anachronisms in Southern Africa and especially those anachronisms which are not in the interest of the United States. But not now.

Don't you feel that if Soviet political and military strength advances as it is now doing, through the Horn of Africa up through the Middle East and down to Afghanistan, maybe in five or six years' time you may wish with hindsight you hadn't discounted Soviet influence quite as much as you are now doing ?

Yes, it is possible. But at the present, if Africa feels dependent, feels unfree, it is because of Western Europe. We are to Western Europe what Latin America is to the United States. So for those Africans who feel they need to enlarge their area of freedom, their problem is not the Soviet Union. Their problem is Western Europe. For Western Europe to tell me, "Julius, don't know the leaders of the Patriotic Front -- they are not insane. They are very shrewd. They understand the value of world opinion. They are not the ones defying the world opinion. The support they get from church people and missionaries is quite clear. It is obvious. It is Smith, not they, who have expelled missionaries from Rhodesia. It would be amazing that in the face of all these considerations the Patriotic Front would go out kiling missionaries. What would they gain now? I know Smith has expelled missionaries. He has expelled nuns -- he has locked them up. We know he has done this. Yet he is the one who says the Patriotic Front is killing them. Why should I believe lies?

Let us now talk about South Africa. I believe you have accepted that the Afrikaaners are a white tribe of Africa. Don't you think there would be more chance of reaching some solution in South Africa if one argued for a federation of states within South Africa, with the whites having their own tribal area ? you worry about us, worry about the Soviet Union because you never know" -- well, I can't talk about "I never know." I talk about what I know. And what I know is the fact that we are dependent on Western Europe and I know that I don't want to be dependent upon anyone else, the Soviet Union included.

You don't get anxious when you see so many Communist troops in Ethiopia and Angola who are seemingly digging in for a long stay ?

I know why they are there. The Cubans are in Angola because the West decided to back up South Africa in its attempt to prevent the MPLA taking over the government of Angola -- a cause they had been fighting for for 10 years. I still approve the reasons why the Cubans are there. The South Africans are even now still menacing Angola. As long as [Angolan President Agostinho] Neto feels menaced by South Africa there is no reason why they should not keep Cubans there.

[Ethiopian leader Lt. Col.] Mengistu had a third of his country occupied by Somalia. What was his alternative? If it had been Haile Selassie and not Mengistu, he may have asked for help from the United States. I would have said he had every right to.

In 1961 you said that you felt one contribution Africa could make to the present history of the world is to refuse to arm. You have certainly changed your views since then. You must have gone through a tortuous period as a committed Christian when you moved from this position to where you now see only armed struggle as the answer to Rhodesia .

No. Frankly, to arm or not to arm has never been a problem for me at all. For me, it has been a political question rather than a Christian one. Violence is a political instrument. I have never seen it as a moral issue. I wish I could. I did try. I took Gandhi very seriously. He believed if India were attacked, they should not fight back. I said I am a Christian, let me see if as a Christian I could reach the same conclusion. I tried to. The New Testament says turn the other cheek. Or the Decalogue: "Thou shalt not kill" -- it is straightforward. There is no "except in certain circumstances." But I can't convince myself at all. And so there I am. It is a shame, but I am not the only one. There are many other Christians who have not reached Gandhi's conclusion.

What do you do when two morally right courses clash? You support the liberation forces in Rhodesia. But then the guerrillas come up against a white family and the father sees his duty to defend his family. For him to kill the guerrillas is morally right. There you have the clash of perhaps two equally valid moral forces. Do you ever worry about that ?

I suppose people do worry. But once you have made the major decision to go to war, you have agreed to take all the risks of war, including the killing of innocents. Even if it were just the guilty on one side it would still be a problem, because it is still human beings being killed. Whether you like them or not, it is better that they live rather than they die.