In a ceremony laden with political symbolism for a president seeking reelection, President Carter gave a warm welcome to the White House to the new leader of Zimbabwe, Robert Mugabe, proclaiming him already a "notable world leader" and the head of a "great new republic."

The president, who played a crucial role in promoting the elections that finally brought Mugabe to power in April, hailed the peaceful transition to black-majority rule in Zimbabwe as a victory for his own human rights policy and justification for his personal interest in black Africa over the past four years.

Carter drew a direct parallel between the struggles to overcome racial strife and reconcile blacks and whites in Zimbabwe and the United States, saying the principals and ideals expounded by Mugage were "very similar, perhaps even identical" to those of this country.

Speaking at a packed reception in the East Room, Carter used the occassion to salute black ambassadors Andrew Young and Donald McHenry, who stood behind him, for what he called their "instrumental" role in the long, tortuous negotiations that finally led to a resolution of the eight-year-long war in the former British colony.

"They never let me forget your stuggle," he told the Zimbabwean prime minister, "and they never let members of Congress forget the burning issues involved . . . in your struggle."

To all appearances, Carter was using the occasion of a rare public appearance with Young, his former ambassador to the United Nations, to shore up his saggine popularity within the black community, where Young is extremely popular and where his resignation over the Palestinian issue a year ago is still deeply resented.

Carter repeatedly praised both Young and McHenry both for their role in the American civil rights struggle and the Zimbabwean negotiations, crediting them with "a major breakthrough" in both fields.

He also quipped that he had asked Mugabe to come to the White House "to observe closely the techniques you have used in your successful political effort" as he himself gears for an uphill struggle in the forthcoming presidential race.

The Zimbabwean leader was effusive in his praise for Carter's "kind of solo effort" in blocking congressional efforts in 1978-79 to force U.S. recognition of the short-lived white-backed government of Bishop Abel Muzorewa and to repeal the economic sanctions in force against it.

Wishing the president well in his difficult campaign for reelection, Mugabe in turn quipped that Carter would be assured of victory if he were running in his country.

Here on a whirlwind, one-day visit to Washington to appeal for more U.S. economic assistance for his hard-pressed government, Mugabe first addressed a gathering of 35 House members and then met with Secretary of State Edmund Muskie for a working lunch before going on to meet with Carter.

"My message," he said after meeting with the lawmakers, was that we need the friendship and solidarity of the United States just as we needed it during the struggle. We want economic solidarity and assistance now."

In his repeated pleas for more aid, Mugabe linked the necessity for it to the future political stability of his country and the success of his efforts at reconciliation between blacks and whites after the long, bitter guerrilla struggle there. He also warned that the peace and stability of the entire southern African region might be at stake, most notably in White-ruled South Africa.

From most accounts. Mugabe made an excellent impression on all the U.S. officials he met during his one-day visit.

Calling him "very articulate" and "reponsive," Rep. Clement J. ZABLOCKI (D-Wisc.), chairman of the House Foreign Affairs Committee who was host at the meeting on Capitol Hill, said that Mugabe "impressed not only myself but I'm sure the other members present."

Mugabe has been seeking $350 million here and in Britain for war reconstruction and the resettlement of 250,000 refugees outside the country as well as "upwards of 2 million" displaced persons inside. He also has mentioned the figure of $5 billion as being needed for a long-term development program.

After meeting with Muskie, Mugabe told reporters that he had not gotten any indication yet of how much more the United States was willing to give his government.

State Department officials said Muskie was generally "supportive" of Zimbabwe's request, but added, "We could not discuss specific numbers now" because of the uncertainty over the whole foreign assistance progran for the present and coming fiscal years.

Zimbabwe is scheduled to receive more than $100 million in loans and grants through September 1981 and could also get another $150 million in loans from the Export-Import Bank. U.S.officials argue that this is already a large slice of total U.S. economic assistance for Africa, suggesting that little more is likely to be forthcoming for the time being.