In two hours yesterday Robert Mugabe, the prime minister of Zimbabwe, worked his dual charisma on two different Washington crowds. When he walked into the East Room of the White House, accompanied by President and Mrs. Carter, he was the statesman, and the applause was enthusiastic and lengthy.It erupted into a stadium-size cheer when Mugabe raised his hands in a victory fist.

At his next stop, Howard University, he was the fiery nationalist. He was greeted by the African call of teacher or "malawi," and applause interrupted every few phrases of his speech. At the end, when he clenched both hands above his head and cried, "Come Home Therefore," the response was deafening.

Referring to the tumultuous reception he has received in New York and Washington and admittedly twisted a slogan of history, Mugabe told the White House reception, "I indeed came, I saw and I was conquered." President Carter said the successful struggle for independence proved that "already you are not only a great leader of your own nation but of the world."

Mugabe, who was ending his first visit to the United States since his party assumed the first black leadership of Zimbabwe in April, used a scholarly manner at the White House. He spoke passionately but softly of his views of demoncracy, racialism, the past history of the country, the international support he and the other freedom fighters received over the years of armed struggle, and the present and future efforts of reconciliation within Zimbabwe.

Repeating the same themes at Howard, Mugabe also rekindled the spirit of racial solidarity. "The occasion is one of a reunion of forces that were together for a long, long time as the struggle was being waged. True, we were not in physical contact (but) we have foght a common enemy, a common enemy who was a settler and who used our own color as a citerion for oppressing us . . . Having defeated them in spite of our color, I am sure you agree this is a moment for us to reunite," said Mugabe.

Basking in the warmth of the response to Mugabe, President Carter asked for some political pointers. "I have also invited you here to observe the techniques of your political success," said Carter, reeling off a lighthearted list of Mugabe's accomplishments in his five-day visit. "We political underdogs have to stick together . . . You have addresed the U.N., had a remarkable rally in Harlem, had appearances on "McNeil-Lehrer," on "Meet the Press," favorable editorials in The New York Times, The Chrisitan Science Monitor, The Washington Post, had lunch with Secretary Muskie, even before we met."

The significance of the late afternoon meeting and the need for continued support of Zimbabwe dominated the after-speech discussion as Mugabe stood in a receiving line, shaking hands with all 500 guests.

"It is really very assuring that a man who was unjustly imprisioned for 10 years can take his place through the democratic process," said Patricia Roberts Harris, secretary of health and human services. "I am sure there were moments he must have despaired."

Rep. Cardiss Collins (D-Ill.) the chair of the Congressional Black Caucus, said, "I hope this support is a symbol of what the administration will do in Namibia and South Africa." Robert Powell of the National Council of Churches, a group that supports the Southern African liberation struggles through fund-raising, lobbying and protests, said, "Both sides (Carter and Mugabe) are trying to be as genuine as their political situation allows. In that context the remarks were warm . . . But we have to be just as diligent on the sanctions and divestiture movements in the rest of South Africa as we have been in the past."

The Washington part of the Mugabe trip had gone well, said his private secretary, Derek Vandersyde. "We probably should have some more time . . . But he has to hurry home for the annual agricultural show, which is a first for him."

Vandersyde worked for former prime minister Ian Smith. "I find it very interesting. My outlook is to help good government. We must remain neutral; that is the strength or the weakness of civil servants," he offered.

In addressing the students, Mugabe also spoke of the continued fight to bring back majority rule to Namibia and South Africa. "Africa, having liberated so many of her territories, mus work to liberate two more . . . We must restore the true dignity of Africa, what Kwame Nkrumah called the African personality. Let us forge ahead in unity," he said.

The rousing cheers were eclipsed a minute later as Mayor Marion Barry was introduced and loudly booed. He presented the key to the city over the noise.

In the audience, one student explained her reaction.Barry, she said, used a lot of occasions "just to be seen.He really doesn't act from his heart." Another, sophmore Camilla Younger, said Barry "deserved the boos. His overall record is unpopular."

As for Mugabe's speech, though, he had been "extremely powerful, especially by inviting us to be one in his fight."