Prime Minister Abel Muzorewa yesterday indicated that he would reject U.S. and British appeals for immediate moves to alter Zimbabwe-Rhodesia's constitution to give the country's black majority more political power now.

Muzorewa said in an interview that he feared that such changes could trigger a complete exodus of Zimbabwe Rhodesia's small but powerful white minority, which the African leader described as "frightened of the new situation."

Muzorewa is expected to hear fresh calls for consittutional changes in a meeting this afternoon at Camp David with President Carter and Secretary of State Cyrus R. Vance.

Muzorewa and Vance yesterday had a 90-minute conversation, which u.s. officials described as "a useful exchange that Vance expects to continue at Camp David."

British Prime Minister Margaret Thatcher was reported from London yesterday to be preparing to stress to Muzorewa Friday that he has to show that he has control of the government formerly headed by Ian Smith.

Throughout a busy day, which included appearances on Capitol Hill before congressional supporters, meetings with labor groups and journalists and the late-afternoon session with Vance, Muzorewa repeatedly said he has moved as rapidly as he could to end racial discrimination and halt the country's guerrilla war.

In his interview at The Washington Post, Muzorewa repeated his offer of amnesty for all members of the Patriotic Front guerrilla forces, including leaders Robert Mugabe and Joshua Nkomo. This offer has been conveyed in personal letters from Muzorewa to the two men.

Asked if he is still prepared to negotiate with them, as he said in October, Muzorewa would say only that he would open a "dialogue" if the guerrillas laid down their weapons and returned home.

Muzorewa told one group of congressional supporters that he also had sent letters to the presidents of Zambia and Mozambi que, offering "good neighbor relations" if they would cease support for the guerrillas.

But he added that he has not received any response from the guerrillas or their supporters "except an escalation of the war" since he took office June 1.

In explaining Carter's June 7 decision to maintain economic sanctions against Muzorewa's government despite strong sentiment in the Senate to end the trade embargo, Carter and Vance stressed the racial inequalities caused by the constitution's entrenchment of white power.

The constitution, approved by whites only, gives the 4 percent white population continuing control of the armed forces and police and a veto power over constitutional change for at least the next 10 years, Vance said.

But after meeting with Vance yesterday, Muzorewa said in response to a reporter's question: "I don't have to take any further steps. People in my country can live wherever they want, they can go to whatever school they want, whatever hospital they want. There is a difference in my country now."

A White House official said Carter would outline for Muzorewa the steps the United States would like to see him take to attain "true majority rule." The White House believes that the meeting will help lessen congressional pressure on Carter for the immediate removal of sanctions, the official said.

During the hour-long interview earlier in the day, Muzorewa sharply criticized Carter's Africa advisers, whom he said had been "brainwashed" by Patriotic Front supporters.

Reffering to Andrew Young, the U.S ambassador to the United Nations, Muzorewa said:

I understand that Mr. Carter's problem is that my black brothers here are threatening him with the loss of reelection if he lifts sanctions. That is the only thing holdng him up".

About 30 persons greeted Muzorewa with hostile shouts and placards as he arrived at The Post at Lunchtime yesterday. Mimeographed statements handed out by the Coalition for a Just Solution in Southern Africa condemned attacks into Zambia and Monzambique by Zimbabwe-Rhodesian forces.

Muzorewa, who is visiting Washington at the invitation of Sen. Jesse A. Helms (r-n.c.), vigorously defended, during the interview the continuing presence of Ian Smith in his government as minister without portfolio.

Muzorewa said he should be commended for keeping Smith in the government, since most African rulers "shoot their predecessors when they come to power."

Smith's presence is a symbol of "our commidtment to democracy" and of Muzorewa's efforts to reassure the country's estimated 200,000 whites, who arc "frightened of the new situation," Muzorewa said.Zimbabwe-Rhodesia suffered a net loss of nearly 1,000 whites in April, recent figures show.

"We can change the constitution when we want to," Muroewa said. "But we don't want to bulldoze change on people, be they a minority or white. We will wait to see what the entire community, black and white, want,"

He said that lifting sanctions would open up new jobs for young people and cause many guerrillas to defect to his side.

"I want all people to come back without fear of detention of death, including Mr. Nkomo and Mr. Mugabe," he said. CAPTION: Picture, Prime Minister Abel Muzorewa: An offer of "good-neighbor relations." By Frank Johnston - The Washington Post