Mayor Marion Barry returned from a three-week African trip yesterday and said he was prepared to mobilize support for African countries that are experiencing drought and economic hardship.

Barry was greeted at National Airport by his wife Effi and son Christopher and a group of about 40 persons, mostly cabinet members and aides, who clapped and chanted "Welcome back, Mr. Mayor. Welcome back."

Barry, who is head of the National Conference of Black Mayors, attended a meeting of the World Conference of Mayors in Monrovia, Liberia, and visited several other African cities, including Addis Ababa, Ethiopia; Dakar, Senegal; Abidjan, Ivory Coast, and Khartoum, Sudan.

As airport travelers looked on in the baggage claim area, Barry, surrounded by staff members and supporters, made a brief statement to the press about his trip and declined to answer any questions about the grand jury investigation of Ivanhoe Donaldson, Barry's top political adviser and chairman of the D.C. Democratic Party.

The grand jury is investigating Donaldson in connection with about $30,000 in checks issued when Donaldson headed the city's Department of Employment Services, according to sources.

When asked to comment on the investigation, Barry said: "One thing that I learned when I was in Africa, the press plays by the rules. And the rules were that we were going to talk about Africa today. I just got back. I've not had a chance to be briefed personally by my staff and you wouldn't expect me to comment on that, would you?"

Regarding the meeting of the World Conference of Mayors, Barry said that the group stressed what they called the five Ts -- trust, trade, tourism, transfer of technology and twin cities.

One city that the mayor visited, Dakar, Senegal, is one of the District's international sister cities and Barry said that he discussed specific programs with officials in Dakar. In general, however, the mayor said that many African countries could benefit from more help from this country.

"There is much pain and suffering there not necessarily created by the governments who are there but by the climate," Barry said of the drought-stricken African countries. " . . . We were able to learn first hand what we can do here, more in the private sector and more in the government sector. I don't think that people ought to be starving, having to die because of not enough food, particularly as powerful as this country is."

Barry said that he got a first-hand look at the leadership of some African countries and admired what he saw. He also said that he plans to spread the world and "mobilize support" for the countries.

"What all the African countries need, I think, is a stronger lobby here in Washington on behalf of the governments in Africa," Barry said. "They are working awfully hard under very difficult circumstances and I admire their leadership for having all those difficult situations and doing all they can to make life a little bit better."

Barry's trip to Africa was his second since he has been mayor. In 1979, he left on a 20-day trip to Senegal, Liberia, Kenya, Zambia and Tanzania and said upon his return said that "we have to be more actively involved" in the struggles in African countries.

Expenses for the mayor's recent trip will be $15,000, most of which will be paid from donations by the private sector, according to city officials.