An exhausted Mayor Marion Barry returned to Washington last night from his 20-day, five-nation trip to Africa and said the example of the Africans he met showed him that his city government "ought to get way more" in services for the tax dollars that are being spent.

Three vanloads of Barry's top city aides and a D.C. police cruiser with flashing lights drove to National Airport to greet Barry and his wife, Effi, and Courtland Cox, the District's minority business opportunity chief.

The smiling mayor said he was glad to be back in the city, but otherwise declined to talk about his specific thoughts on the trip until he holds a press conference tomorrow.

Earlier in an interview with The Washington Post on the last leg of his trip on board a shuttle flight from New York to Washington, Barry talked about some of his feelings during the journey that took him to Senegal, Liberia, Kenya, Zambia and Tanzania.

The mayor said that in every country he visited he found that impoverished nations with limited resources often perform many governmental services that require much larger numbers of people and more money in the United States.

"I'm a very tough taskmaster, insisting the citizens get services," Barry said. "We're going to insist we do more."

Several of the African cities and institutions that Barry visited requested aid of one sort or another and the mayor often promised to see what the could do to help. But on the flight home he said that before anything is done he wants to take some time to evaluate the various requests with his wife, Cox and two others who accompanied him on the trip, D.C. Democratic Party Chairman Robert B. Washington and Riggs National Bank vice president Carter H. Dove.

"I would suspect we'll be able to influence the U.S. government to do a little bit more than they're doing," Barry said.

But personally, Barry said he came away from Africa with a feeling that as a black person "I have a responsibility to help where I can.

"Even though we have problems of our own," the mayor said, "we can't be too busy to ignore the problems of others.

"I'm going to have to educate some of my friends about what is the correct strategy about American business in South Africa," Barry said. "We have to take the leadership from the Africans.

"Everyone who invests in South Africa should denounce apartheid as inhumane and immoral," he said. "It is also clear that American businesses shouldn't be there."

Barry's flight from Rome was delayed 2 1/2 hours and as a result he missed his initial flight connection back to Washington. When he arrived at John F. Kennedy International Airport in New York, Pan Am had a limousine waiting to whisk him to LaGuardia Airport for the flight back to Washington.

But before he was driven to LaGuardia, Barry and Cox walked to a newsstand to buy at copy of the latest issue of Time Magazine, which calls Barry one of the "Fifty Faces for America's Future." Barry quietly read the article between the airports.

About 30 well-wishers greeted Barry at National Airport and Effi Barry was handed a bouquet of yellow roses. Among the greeters were city administrator Elijah Rogers, executive secretary Dwight Cropp, budget director Gladys Mack, housing chief Robert Moore, and Barry's top aide, Ivanhoe Donaldson.

While the aides waited for Barry to arrive, Donaldson passed the time greeting weary-looking passengers, telling the curious that the mayor was coming back from "whirlwind trip to Africa."

"Welcome to the District of Columbia," he exclaimed to the puzzled passengers, none of whom appeared to know who he was.

Rogers was acting mayor while Barry was out of the city, but last night he quickly found that he no longer was the boss.

On the way to National Airport, Rogerts rode in the mayor's telephone-equipped Ford LTD.

He traveled back to the city in a dusty sedan that was mistakenly whistled to a halt by a policeman directing traffic. Sam Jordan, a trouble shooter for the mayor, spotted the goof and held up traffic while Rogers' car fell in line behind the mayor's.

U.S. taxpayers wound up paying $2,500 for Barry's travels and another $2,500 for Cox's air fare and per diem expenses, according to the trip's sponsor, the U.S. International Communication Agency. The expenses of the other three members of the Barry entourage - Effi Barry, an assistant vice president for marketing with Pacific Consulting, Washington and Dove - were either paid for by themselves or their firms.

The mayor first broached the idea for the combination vacation and working trip to the ICA three months ago, according to Michael Baskin, the ICA official who arranged Barry's itinerary.

Baskin said the mayor had received an invitation from Francis A. Dennis, Liberian ambassador to the United States, to attend the Organization of African Unity meeting in Monrovia as an observer.

Baskin said the ICA then sent messages to the U.S. embassies in the four other countries Barry wanted to visit to arrange his itinerary in those countries and meetings with mayors and heads of state there.

The ICA regularly pays for foreign travels of prominent Americans to discuss various aspects of U.S. life, and financed a similar trip to Africa earlier this year for Atlanta Mayor Maynard Jackson.

"Marion Barry was an ideal person" to go to Africa, Baskin said. "He's the mayor of our capital city; a black, a civil rights leader, somewaht radical in fact; and now he's made it in our system" of government. CAPTION: Picture, Mayor Marion Barry displays carvings from Tanzania on his return to D.C.