Tanzanian President Julius Nyerere today strongly urged Britain and the United States to intervene militarily in Rhodesia and forestall the prospect of a bloody civil war.

He said that the Western powers should use force to impose their plan for U.S.-supervised elections that would bring black majority rule. He warned, however, that such an intervention must not be staged on the pretext of rescuing Rhodesian whites while, in fact, backing one black nationalist faction against th other.

Nyerere was the first African leader to speak frankly about the likelihood of a bloody power struggle between Rhodesian black nationalist factions once the white -- dominated government collapses.

Nyerere's remarks in an interview clearly under-scored his fears that such a time is approaching and was rejected by the guerrilla factions -- still holds the best hope for a peaceful resolution of the Rhodesian conflict.

Observers of Rhodesian affairs believe that a Western military intervention was highly unlikely.

"We are not asking for something contrary to U.S. principles in Rhodesia, just an elected government," he said.

The Tanzanian leader expressed great concern about the growing prospects of an Angolan-style civil war between the two factions of the Patriotic Front, the guerrilla alliance fighting to topple the white-led Rhodesian transitional government.

He said he did not think either black Africa or the United Nations would seriously oppose British military intervention in Rhodesia at this time provided its purpose was to implement the stalled Anglo-American proposals for a peaceful transition to black majority rule under combined U.S.-British supervision.

"I think they can go in," he remarked." They would go in for a period of six months and decolonization would begin. It wouldbe very difficult for the Patriotic Front to get Africa to go against this."

Nyerere, like other black African leaders, regards Rhodesia as still primarily a British responsibility and colony, albeit a rebel one since the unilateral declaration of independence by the whites there in November 1965. Under the British-American proposals, Britain would again take power and then procede to "decolonize" the country by holding elections for a legitimate black majority government.

The Tanzanian president said he saw no chance for the success of the proposed British-American peace conference on Rhodesia at this time. British Prime Minister James Callaghan and President Carter are scheduled to discuss the advisability of holding one during the four power meeting in Guadeloupe this weekend.

Neerere, who is chairman of the five frontline African states involved in the Rhodesian issue, said he saw "no evidence it is worth calling." Some parties, including the Patriotic Front, would not attend, he predicted, and the necessary conditions for such a conference had not been fulfilled.

Chief among these, he said, was the acceptance by Rhodesian Prime Minister Ian Smith of the basic provisions of the Anglo-American plan.So far, Smith has only said he will attend a conference provided there are o preconditions.

Nyerere also seems to feel that if Britain does not intervene now in Rhodesia to impose U.N.-supervised elections, then it is much more likely to become involved militarily if and when a civil war does break out.

"The British will go in not to rescue the whites but to take sides," he said, adding, "I cannot see the Americans opposing them."

Although he did not say so explicitly, he indicated he suspected the British in such circumstances would maneuver to help the Aimbabwe African People's Union (ZAPU) under Joshua Nkomo to seize power with American blessings against the other faction of the Patriotic Front, the Zimbabwe African National Union (ZANU) led by Robert Mugabe.

Nkoino's group is based in Zambia and Mugabe's in Mozzmbique. So afr, there hs been no military and little political cooperation between the two factions.

The Tanzanian leader, interviewed at his seaside home outside the capital, seemed far more preoccupied with the fast deteriorating situation in Rhodesia than with his own recent border war with neighboring Uganda.

Full scale fighting ended in mid-November after a two week war. Tanzanian troops drove some 3,000 invading Ugandans out of the area north some 3,000 invading Ugandans out of the area north of the Kagera River in northwest Tanzania.

Both sides are reportedly keeping sizable forces in the border region but Nyerere said "we havr refused to go across." He denied he was seeking the downfall of Ugandan President IdiAmin in revenge.