"It's been rough," Andrew Young, the U.S. Ambassador to the United Nations for nearly two months now, admitted yesterday. "It seems that every time I open my mouth, I put my foot in it. Well, I've got a big mouth, and I intend to keep opening it."

The audience applauded wildly. It was that kind of effusive and praising audience that every politician loves. Even before Young and Vice President Walter Mondale addressed the National Newspapers Publishers Assn. (NNPA) yesterday, both were cheered boisterously.

On Thursday evening, Young declared, President Jimmy Carter had not only endorsed Young's outspokenness but said he would continue speaking out for human rights also. "Carter said to me, 'I hope you're going to stick with me. It gets kind of rough out there. People aren't used to discussing American foreign policy in advance. I don't intend to shut up and I shop you wouldn't let them intimidate you either.'"

At the luncheon meeting of the NNPA, Young compared the civil rights movement of the 1960s to U.S. policy toward South Africa today. "It's going to be very difficult for the United States to maintain any kind of relations with the Republic of South Africa if they continue the policy of apartheid"

The publishers association, which represents the majority of the 200 black newspapers in the United States, is meeting here this week during the 150th anniversary of the founding of the black press. Yesterday historian Dr. Jay Saunders Redding addressed 300 people at a cerenemy dedicating a Black Press Archives, a joint project of the NNPA and Howard University.

Earlier Mondale had tole the publishers, "your words are needed," and suggested issues for the black press' consideration. "Next week we are sending a message to Congress on revising the election laws in this country. We think it should be easy to vote and there should be no artificial barriers, especially for working people and the poor," he said.

Other editorial issues, he said, included the administration's decision to refuse to buy Rhodesian chrome, and unemployment - especially among black teen-agers, now 26 per cent of the nation's unemployed youth.