U.S. Ambassador to the United Nations Andrew Young, in a speech at his alma mater, Howard University, yesterday urged black Americans to take a more active role in governing this country and in shaping U.S. foreign policy toward black Africans.

"We ought to get about the business of shaping the destiny of this nation because it has shaped us too much and we don't like the image," Young told an enthusiastic audience of students and faculty at the predominantly black university.

"Black men and women in the United States can never be free as long as black men and women in South Africa are not free," he said.

Speaking on broad foreign policy issues in a manner uncharacteristic of pervious, more cautious U.N. ambassadors, Young said there was no way of separating foreign affairs from gut domestic issues such as unemployment, and urged the students to lobby Congress and get involved in the political process.

He told the students to "see your congressman about repeal of the Byrd amendment," which makes it illegal for the U.S. to boycott Rhodesian chrome.

"The vote on the Byrd amendment," Young said, "is a vote on the commitment of the United States on majority rule in Africa. You can make an impact by letting your congressman and senator know that you are concerned."

We came out of the Kennedy and Johnson years with excellent domestic programs," the former Georgia congressman said, "but they foundered on the shores of Vietnam."

Young quoted the words of his late mentor, the Rev. Dr. Martin Luther King Jr., that "the bombs you drop in Vietnam will explode at home." He linked economic, racial and drug problems of the late 1960s and early 1970s to the Vietnam war, and added that ultimately "you pay the price with a Watergate at home."

Young expressed faith in the moral leadership of his fellow Georgian, President Carter and said that under the leadership of Richard M. Nixon and Gerald R. Ford, the nation became "morally retarded."

He said the black vote decided the election for Carter and "I don't know about you, but I'm not disappointed."

Young said that hardly a Cabinet meeting goes by without Carter asking the members, "'How are you doing in hiring minorities and women?'" (an area in which the President has been criticized for not fulfilling campaign promises).

"Perhaps this south Georgia President," he added, "might well be the one who can move this nation, with our help, beyond the stigma of race and class."

Just to elect the President, though, Young said, "doesn't assure that the kingdom has come. The burden is still on us to cry out for freedom and justice."

Young said that blacks, rightly, had been America's best critics, but "because this system has produced more than any other," they also "have a responsibility to be its best advocates."

To illustrate the need for young blacks to involve themselves in the world as it is, Young noted that at the corner of Jomo Kenyatta Boulevard and Uhuru Avenue in Nairobi there was a Kentucky fried chicken store.

"If you're going to be on this planet," Young said, "you can't escape from the man. You might as well deal with him right where you are."

He said that Alex Haley's book "Roots," "forced us together to understand the horror of slavery and our African identity," but he warned the students "not to get so absorbed that we forget we are Americans."

Young, who spoke without notes, made his remarks at a convocation noting Howard's 110th anniversary. Young, who graduated from Howard in 1951, received an honorary doctor of laws yesterday. He jokingly referred to the doctor of laws as his second honorary degree from Howard.

Recalling his days as a student there, Young talked about the enriching experience of meeting foreign students at the university, and said that when he went to Nigeria a few weeks ago it was "not as it I was going to a foreign land, but as if I was going to meet classmates and brothers."

The Nigerian ambassador to the United States, Edward Olusola Sanu, attended Howard when Young was there. The ambassador received an alumni postgraduate achievement.

Young also said that he was introduced at Howard to the nonviolent philosophy of Mohandas K. Gandhi, which he later put into practice with Dr. King as an official of the Southern Christian Leadership Conference.

When a former president of the university got to Gandhi in his chapel sermon, Young said, "I knew it was 10 minutes from lunch." After the audience laughed, Young added, "But something got to me and I checked out Gandhi and when I got to Martin Luther King I was ready."

Young ended his half-hour speech by saying, "We and all we stand for shall overcome." He was given a standing ovation.