The United States and Britain intend to seek early approval by the United Nations for their peace plan in Rhodesia.

David Owen the British foreign secretary and Andrew Young, the U.S. ambassador to the United Nations, joint authors of the initiative, told a press conference here today that they hope to launch their bid for Security Council endorsement by the end of the month.

Then, Kurt Waldheim, the U.N. secretary general, is expected to name as special U.N. representative a military man who will lead a proposed U.N. peacekeeping force. This officer and Field Marshal Lord Carver would next embark on the difficult and crucial task of bringing rival black and white Rhodesian forces to agree on a cease-fire.

Carver, Britain's former chief-of-staff, has been chosen by London to serve as resident commissioner or commander on the scene until Rhodesians choose a new government through nationwide voting.

The United Nations plays a critical role in the Anglo-American plan. Along with Carver, its special representative is to meet secretary with black and white military commanders to obtain the all-important end of hostilities.

U.N. members are to be called on to supply troops to help Rhodesian police, commandeed by Carver, maintain order from the time of the cease-fire until the newly elected government is installed.

Finally, Security Council approval of the board lines of the Anglo-American proposal is expected to bring political pressure on the combatants, to isolate foes of the plan.

Owen was asked whether he thought the Soviet Union or some other power might veto the plan in the Security Council. He answer that if the Organization of African Unity supports the plan, a veto is unlikely. The OAU, in turn, is expected to back the plan proving that it has the support of Rhodesia's live black neighbouring states - Zambia, Mozambique, Botswana, Angola and Tanzania.

Owen and Young have just returned from an African tour where they saw leaders from this group, and the two envoys appeared optimistic about U.N. approval.

But getting the Security Council's assent is only the first step on a harroa. The central question is whether Prime Minister Ian Smith's white regime and the four rival Rhodesian black leaders - including two who run guerrilla armies - will agree to stop their war. Until that happens, on U.N. peacekeeping force will move in, Carver will not take up his residence and there will be no elections.

Up to now, the belief has been that black nationalist leaders Robert Mugabe and Joshua Nkomo would settle for nothing less than a handover of military power to their armies. The Owen-Young plan rules this out.

But Young's aides insist that this is no longer a stumbling block. Each of the black leaders - Mugabe, Nkomo, Bishop Abel Muzorewa and the Rev. Ndabaningi Sithole - is said to be convinced he can win a fair and unintimidated election.

It is hoped that the five front-line states who give the guerrillas their base will help them accept neutral supervision of a vote. The five are said to be concerned with the guerrillas' failure to wipe out Smith's forces quickly. Young observed that a prolonged struggle will drain resources from their own troubled economics.

On the other side, Smith may be a tougher nut to crack. Owen insisted that Smith's security situation has deteriorated and he knows it." Whether his military commanders will prove responsive to Carver and Waldheim's representative is a question.

In the end, U.S. diplomats are counting on South African Prime Minister John Vorster to conclude that the Anglo-American plan serves his interest and press Smith to agree. Just as the blacks depend on the "front-line" five to survive. Smith's government exists on Vorster's sufferance.

Young observed that "The overall potential of this situation to degenerate into something like the situation in the Horn of Africa we think is serious enough for us to put a major commitment in place."