President Carter, responding to the growing impatience of black Africa for an end to white minority rule in southern Africa, promised yesterday to step up American efforts to bring black majority rule to Rhodesia.

The United States, Carter said, "now will move as quickly as possible to call together the parties who are in dispute in Zimbabwe," the black nationalist name for Rhodesia, which Carter regularly uses.

U.S. officials said later that efforts are already under way to arrange such a meeting, which would be hosted by the United States and Britain, but they acknowledged that they had no assurances that all sides were willing to take part.

While Carter and Nigerian ruler Lt. Gen. Olusegun Obasanjo seemed to be in agreement on Rhodesia in their two days of talks, which ended yesterday, it was clear that they did not reach complete accord on two other major issues they discussed: the presence of Cuban and Soviet military personnel in Africa and the amount of pressure Western powers should put on the white minority government of South Africa.

Carter spoke of the Rhodesian situation with reporters after his second meeting with Obasanjo. Today Carter leaves Nigeria for a brief visit to Liberia, the last stop in his four-nation trip to South America and Africa. He is to return to Washington tonight.

U.S. officials said there was no indication that the white and black leaders of Rhodesia would attend such an all-parties conference. Recently, Prime Minister Ian Smith has said he would "consider" participating in a conference involving all parties, but black, locally based leaders have shown little enthusiasm for one.

The "front-line" states that border Rhodesia and the Patriotic Front, the guerilla alliance of Rhodesian black nationalists, have said they would attend an a attend an all-parties conference if it were based on the Anglo-American proposals for majority rule. However, they want the British and Americans first to hold a limited conference with the Patriotic Front to complete their negotiations started last January on Malta regarding military issues and the transitional period leading to black majority rule.

Whether the United States will actually succeed in bringing all the factions together for a meeting was far from clear. However, the announcement of a renewed American effort to bring the parties in the Rhodesian dispute together served to underscore the president's rhetoric here about his continued commitment to the Anglo-American plan.

Nigeria and other black African nations support that plan and strongly oppose the so-called "internal settlement" for majority rule reached earlier by the Smith regime and local black leaders.

Details about the proposed Rhodesian meeting were sketchy. Zbigniew Brzezinski, the White House national security adviser, said that no time or place has been set but that an initial meeting is likely to be held in April and be dubbed Malta II. It would involve foreign ministers from the United States, Britain and the African front-line states, and the Patriotic Front.

Following this meeting, Brzezinski said, there would be a second involving the Malta II participants and representatives of the Rhodesian regime.

Carter spoke of the Rhodesian situation with reporters after his second meeting here with Obasanjo. It was clear by the end of the talks that the United States is now more firmly aligned than ever with the black African nations on the question of Rhodesia.

In a joint communique signed last night, Carter and Obasanjo said they agreed that the "internal" settlement in Rhodesia "does not change the illegal character of the present regime and is unacceptable as it does not guarantee a genuine transfer of power to the majority . . . ."

Carter has stressed his concern in recent days about the growing number of Cuban troops in Ethiopia and their involvement in its war over the attempted secession of Eritrea. Carter raised the Ethiopia subject with Obasanjo but there was no mention of the subject in the joint communique, apparently indicating a lack of agreement.

On Saturday, Carter had laid a wreath at the memorial for Nigerian soldiers who fell in the 1967-70 Biafra war of seccession -- a conflict akin to that in Eritrea. Nigerian allegations that the United States had favored Biafra have long complicated U.S.-Nigerian relations.

On the South Africa question, Carter acknowledged that Obasanjo "would be more inclined to take additional embargo action against South Africa than would we."

The communique also made clear the impatience of black African leaders on the issue of apartheid in South Africa.

Obasanjo, according to the communique, told Carter of his "strong disappointment at the lack of impact of the many concrete proposals put forward in the past to eradicate the obnoxious system of apartheid. This he asccribed to the inadequacy of the measures adopted as well as the lack of political will on the part of nations called upon to implement these measures."

American officials, however, made it clear that the United States will not accede to black African demands for increased economic sanctions against South Africa.

"We have the view," Brzezinski said, "that political change may be beginning to occur within South Africa itself in the sense that there is rising a greater awareness to accommodate and that it would be inopportune to take certain measures prematurely."

The issues of majority rule and race relations tended to dominate the president's visit here and little else of substance appeared to result from his talks with Obasanjo.