It wasn't the best of days for Assistant Secretary of State Richard Moose, who is accustomed to congressional assaults on U.S. policies in Africa.

Appearing before a House subcommittee, Moose sought to justify a $20 million foreign aid appropriation to Zaire for 1981 by stressing the political imporantce of that country. Instead, he found himself before in a political buzz saw.

"Why try to pass political money as developmental assistance," the subcommittee's chairman Rep. Clarence D. Long (D-Md.), said in opening a lengthy assault on the entire U.S. foreign aid program.

"My favorite definition of foreign aid is that it involves taking money from the poor people in rich countries and giving it to the rich people in poor countries," said Long, chairman of the House Appropriations Committee's subcommittee on foreign operations.

All this aid "is walking-around money for the secretary of state," Long continued, in a reference to money traditionally dispensed on election day by political parties in Long's home state.

"If we are going to rent military bases, let's rent them and not pretend that we are saving the poor people."

The Maryland Democrat then went on to assert that the United States has been giving "developmental aid for the wrong reasons" and that most of such aid "is not for the people; it is done in the name of the people." The entire program is a "mockery," he added.

After Long's monologue, Goler T. Butcher, assistant AID administrator for Africa, said she was "still a strong supporter of developmental assistance to Zaire."

Yesterday's hearing appeared to foreshadow an uphill struggle for the Carter administration, which is seeking to avoid sharp cutbacks in its foreign aid program during an election year. But it also suggested an increased congressional focus on Zaire, whose government has been accused of widespread corruption and human rights violations in recent months.

Long's attack on the entire foreign aid program was sparked by questions during yesterday's hearing about the government of Zairian President Mobutu Sese Seko and allegations that about 40 percent of that country's revenues wind up in the pockets of senior Zairian officials.

Moose, who is the State Department's top official on Africa, was testifying on behalf of the request of $533 million in aid to Africa. The requested appropriation for Zaire amounts to $20 million.

Moose acknowledged that there were "difficulties" related to allegations about corruption in Zaire. But he said that "progress" has been made in that area during the past years.

He defended the administration's policy, however, on grounds that Zaire, as Africa's third largest country and endowed with natural resources, was of great political importance to the United States.

"It is better to hang in there and try to work with the Zairian authorities," Moose argued, than pull out and open the door to potential instability in all central Africa.

Underlying his argument was the administration's belief that ending U.S. aid to Zaire, including the small $8 million in military support, would indirectly destabilize Mobutu's pro-Western government.